WO2022194404A1 - Multi-material rail pad and method for manufacturing same - Google Patents

Multi-material rail pad and method for manufacturing same Download PDF

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Publication number
WO2022194404A1
WO2022194404A1 PCT/EP2021/076703 EP2021076703W WO2022194404A1 WO 2022194404 A1 WO2022194404 A1 WO 2022194404A1 EP 2021076703 W EP2021076703 W EP 2021076703W WO 2022194404 A1 WO2022194404 A1 WO 2022194404A1
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WO
WIPO (PCT)
Prior art keywords
pad
rail
loa
damping element
rail pad
Prior art date
Application number
PCT/EP2021/076703
Other languages
French (fr)
Inventor
Christopher Plummer
Holger Frauenrath
Oguzhan OGUZ
Véronique MICHAUD
Adrien DEMONGEOT
Joel CUGNONI
Maurice AMMANN
Armin ZEMP
Benjamin Morin
Original Assignee
Ecole Polytechnique Federale De Lausanne (Epfl)
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ecole Polytechnique Federale De Lausanne (Epfl) filed Critical Ecole Polytechnique Federale De Lausanne (Epfl)
Priority to EP21786158.2A priority Critical patent/EP4308760A1/en
Publication of WO2022194404A1 publication Critical patent/WO2022194404A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
    • E01B9/00—Fastening rails on sleepers, or the like
    • E01B9/68—Pads or the like, e.g. of wood, rubber, placed under the rail, tie-plate, or chair
    • E01B9/681—Pads or the like, e.g. of wood, rubber, placed under the rail, tie-plate, or chair characterised by the material
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
    • E01B9/00—Fastening rails on sleepers, or the like
    • E01B9/68—Pads or the like, e.g. of wood, rubber, placed under the rail, tie-plate, or chair
    • E01B9/681—Pads or the like, e.g. of wood, rubber, placed under the rail, tie-plate, or chair characterised by the material
    • E01B9/683—Pads or the like, e.g. of wood, rubber, placed under the rail, tie-plate, or chair characterised by the material layered or composite

Definitions

  • the present invention pertains to the field of material science and engineering.
  • the invention relates to a multi-material rail pad having improved mechanical and/or acoustic features.
  • Rail pads are known from the prior art as compliant (low stiffness) elastic sheets typically made of a polymer-based material that are inserted between the rails and sleepers as part of a rail fastening system.
  • the primary function of elastic rail pads is to protect the sleepers from transient static and dynamic loads due to passing trains without compromising the mechanical stability of the ensemble of the track.
  • the presence of compliant layers between the rails and the sleepers ensures uniform loading over the whole of the rail-sleeper contact area, thus avoiding locally high stress concentrations that may result in damage to the sleepers.
  • compliant elastic rail pads allow the rails to bend more freely than when such rail pads are absent, so that the loads due to passing trains are more evenly distributed over the ensemble of the sleepers.
  • This not only further reduces the maximum transient loads on the sleepers but also reduces the maximum loads on the ballast and substructure, which in turn reduces degradation of the ballast and substructure, and the rate of settlement of the ballast, and hence the frequency with which the track needs to be maintained.
  • the increased freedom of the rails to bend also allows them to vibrate more freely in response to load fluctuations whose frequency is in the audible frequency range, which arise mainly from irregularities in the metallic wheel-rail interface. This leads to significant increases in rail vibration and hence radiation of airborne noise when a train passes over a track equipped with compliant elastic rail pads, with highly undesirable consequences for the environment.
  • EVA ethylene vinyl acetate
  • HDPE high density polyethylene
  • PU polyurethane
  • EPDM crosslinked ethylene- propylene-diene monomer
  • NR natural rubber
  • a typical rail pad is plate-shaped but may also include internal porosity or external studs or ribs or other types of profile on one or both major faces (i.e., those faces in direct physical contact with the sleepers and the metallic rails), that serve to better distribute the load on the pad and reduce abrasion, as known from EP2990529.
  • the thickness of rail pads in the trade typically varies from 4 to 15 mm in the unloaded state, but their effective thickness in service in the absence of additional loading by a train is determined by its stiffness and clamping load, which is typically from 7.5 to more than 20 kN depending on the fastening system.
  • the horizontal dimensions of the rail pad are chosen according to the track geometry. For example, rail pads for use with UIC54 rail profiles are 180 mm long and 140 mm wide, while for UIC60 rails the rail pads are 180 mm long and 148 mm wide.
  • rail pad material, additives and geometry are chosen according to the desired vertical and lateral stiffness in compression and shear under static and dynamic loading, which depend in turn on the type of fastener used to fix the rail to the sleeper and the intended type of rail traffic. Regardless of how they perform with respect to noise, rail pads must have lower stiffness than the rails and sleepers, and must show reproducible and substantially reversible behaviour with respect to large quasi-static and impact loads if they are to fulfil their primary function, namely protection of the superstructure of a ballasted railway track from repeated deformation due to axle loads, which are typically up to 22.5 tonnes in Europe, corresponding to a maximum static or quasi-static force of roughly 110 kN per bogie (set of wheels).
  • Rail pads must also provide a stable support to the train in straight and curved track sections and, in addition to meeting basic static mechanical property requirements, show adequate resistance to creep and fatigue, long term abrasion, moisture, ozone, UV radiation, hydrocarbons and other railway-related chemicals over an extended continuous use period at temperatures between about -20 and 60 °C.
  • the stiffness of the rail pad may then be selected by choosing a material with the appropriate elastic response from the wide range of polymer-based materials that meet the basic design requirements. Because stiffness is determinant for their primary function, rail pads are classified as either "hard” (nominal through-thickness compressional stiffnesses in the range of 200 to as much as 1'300 kN/mm) or "soft” (nominal through-thickness compressional stiffnesses in the range of 30 kN/mm to 150 kN/mm), hard rail pads generally being considered to provide less efficient protection to the track superstructure than soft rail pads.
  • the effective stiffness for a given material may be modified by adjusting the rail pad geometry, prevalent industrial design strategies including the use of studs or ribs on its major faces and/or controlled internal porosity, which serve to reduce the constraints on lateral expansion due to friction with the rigid substrates.
  • Manufacturers of soft rail pads also exploit porosity to reduce the effective loading area of the matrix and hence vary the rail pad stiffness at constant thickness without the need to modify other matrix properties. Both porosity and external profiles also provide a means of engineering the non-linear response of the rail pad.
  • a rail pad may hence be designed to show a soft static response to small deformations, but a higher effective stiffness and hence a harder response as the deformation increases.
  • rail pad materials are chosen primarily for their elastic properties and mechanical and dimensional stability. Most common materials show no major thermomechanical transitions in the range of frequencies, loads, and temperatures of relevance to rail pad operation, which offers the advantage of a uniform elastic response over a wide range of service conditions.
  • prior art rail pads are optimized with respect to elasticity, stiffness, and durability, so that they provide the desired levels of sleeper and ballast protection over long periods of time.
  • high stiffness, hard rail pads with compressional stiffness in the direction perpendicular to the plane of the rail pad k > 250 kN/mm, which limit the freedom of the rails to bend, are preferred for limiting airborne noise
  • low stiffness, soft rail pads with compressional stiffness in the direction perpendicular to the plane of the rail pad k ⁇ 120 kN/mm which provide greater decoupling of the rails and the sleepers and improve sleeper and ballast protection, lead to increased noise.
  • simultaneous optimization for noise reduction and superstructure protection is not possible.
  • noise and vibration damping that is, the restraint of vibratory motion (which may in turn cause noise) through energy dissipation, may be promoted through use of materials that show strong intrinsic damping, including many highly viscoelastic polymers.
  • the ratio of the static stiffness to the dynamic stiffness under load is optimized by a special form of the plate-shaped rail pad, as defined in the relevant test standards EN 13481-2-C and EN 13146- 9.
  • the rail pad comprises ribs and/or crossbar elements with a different stiffness to the bulk of the rail pad, but these elements are not stated to show strong intrinsic damping or strongly frequency dependent stiffness.
  • Noise reduction with respect to a plausible" rail pad static stiffness 100 kN/mm.
  • the results indicate that these pads do not to reduce noise with respect to a standard rail pad with the same static stiffness of 60 kN/mm. No improvement of superstructure protection has been reported.
  • an object underlying the present invention is to provide an improved rail pad that enhances an elastic decoupling between the rail and sleeper under static and low frequency compressive loading, hence shielding the track superstructure from damage due to transient load peaks during train pass-by and limiting low frequency ground-borne vibrations, while not increasing airborne noise over existing technical solutions.
  • Another object underlying the present invention is to reduce rail vibration and radiation of airborne noise over a large part of the audible frequency range between 20 and 20 ⁇ 00 Hz while not increasing track superstructure damage due to transient load peaks during train pass-by and limiting low frequency ground-borne vibrations.
  • a further object of the present invention is to provide a manufacturing method for the multi-material rail pad according to the present disclosure.
  • a rail pad comprising: a) a pad matrix comprising or consisting of a first material and b) at least one damping element at least partially encapsulated or embedded in the pad matrix, said damping element comprising or consisting of a second material, wherein the second material of the at least one damping element has a damping factor tan delta > 0.5 at a frequency of 1000 Hz at room temperature.
  • the above-mentioned objects are at least partially solved in that the method comprises the steps of: a) preparing in a preform at least one damping element comprising or consisting of a material having a damping factor tan delta > 0.5 at a frequency of 1000 Hz at room temperature; b) introducing in a mold the before-prepared at least one damping element; and c) performing a multi-step molding process to at least partially encapsulate or embed the at least one damping element with a pad matrix.
  • rail pads according to the present invention fulfill all the standard technical requirements for track performance and stability over time and in the temperature range corresponding to service conditions.
  • the invention is based, at least in part, on the observation that in conventional single-material rail pads known from the prior art, noise mitigation is predominantly due to coupling of the rails to the sleepers, ballast and track substructure, which is determined in turn by the rail pad dynamic stiffness.
  • Materials such as EVA, HDPE, PU, EPDM rubber, with suitable elastic performance and durability, and in particular resilience, do not show significant intrinsic materials damping when deformed in the audible frequency range.
  • the at least one damping element takes up or constitutes between 10 and 90% of a total volume of the rail pad.
  • the rail pad comprises a single damping element.
  • the rail pad comprises a plurality of damping elements.
  • said at least one damping element has a polygonal or circular cross-section in at least one plane, forming cuboids, spheres, ellipsoids, cylinders, or prisms.
  • said at least one damping element comprises a plurality of monodispersed or polydispersed particle-like units.
  • said plurality of monodispersed or polydispersed particle-like units have an average dimension comprised between 50 nanometers and 1 millimeter.
  • the at least one damping element is configured as a sheet or film.
  • said sheet or film comprises at least one corrugated surface.
  • said at least one damping element comprises or consists of at least one material selected from a non-limiting list comprising polyisobutylene (PIB), crosslinked polyisobutylene (butyl rubber, IIB), polyurethane elastomers (PU), polymer-modified bitumen, polar polymers, such as nitrile, hydrogenated or carboxylated nitrile rubber (NBR, HNBR, XNBR), chlorinated polyolefins (for example, polychloroprene (CR), chlorinated polyethylene or polypropylene, or chlorosulfonated polyethylene), acrylate rubbers (ACM) or epoxidized rubbers (ER), particularly where these have been modified with polar fillers and/or plasticizers or antiplasticizers, conventional vulcanized rubbers such as natural rubber (NR) or synthetic polyisoprenes (PI), polybutadiene (PBD), styrene-butadiene rubber (S)
  • polar polymers such
  • These materials may be further processed into composites that may contain additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, calcium carbonate, talc, kaolin, wollastonite, rubber particles, polymer foam beads, cellulose or cellulose-based materials, cork particles or metallic inclusions.
  • additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, calcium carbonate, talc, kaolin, wollastonite, rubber particles, polymer foam beads, cellulose or cellulose-based materials, cork particles or metallic inclusions.
  • said pad matrix comprises or consists of at least one material selected from a nonlimiting list comprising crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene-propylene-diene monomer (EPDM) rubber or natural rubber (NR), synthetic cis 1,4-polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene- butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as isotactic polypropylene-vulcanized ethylene-propylene-diene-monomer (EPDM) blends, copo
  • These materials may be further processed into composites that may contain additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, calcium carbonate, talc, kaolin, wollastonite, rubber particles, polymer foam beads, cellulose or cellulose-based materials, cork particles or metallic inclusions.
  • additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, calcium carbonate, talc, kaolin, wollastonite, rubber particles, polymer foam beads, cellulose or cellulose-based materials, cork particles or metallic inclusions.
  • said pad matrix and/or said at least one damping element comprises at least one of pores, cavities and voids.
  • said pores, cavities and/or voids are sized and distributed so that the pad matrix and/or the at least one damping element is configured as a close- celled or open-celled foam.
  • said rail pad further comprises one or more stiffness modifying element(s) comprised within or onto the pad matrix, and separated from the at least one damping element.
  • the one or more stiffness modifying element(s) comprises or consists of a material that increases the stiffness of at least a portion of the pad matrix, relative to the stiffness of the pad matrix itself, by having elastic moduli at least one of which is higher than the corresponding matrix modulus.
  • the elastic moduli may comprise at least one of a bulk, shear or tensile modulus, or any one of the independent moduli shown by an isotropic material.
  • the one or more stiffness modifying element(s) comprises or consists of a material that decreases the stiffness of at least a portion of the pad matrix, relative to the stiffness of the pad matrix itself, by having elastic moduli at least one of which is lower than the corresponding matrix modulus.
  • the one or more stiffness modifier(s) has or have a polygonal or circular cross-section in at least one plane, forming cuboids, spheres, ellipsoids, cylinders, or prisms.
  • At least one stiffening modifier is being introduced into the mold before performing the multi-step molding process.
  • Another alternative or additional method is coextrusion using two or more conventional single or twin screw extruders or one or more conic extruders, for example, sending separate thermoplastic materials feeds, including porogens or reactive components if desired, into a single die to produce, in a continuous process, a continuous solid or foamed object with a uniform cross-section perpendicular to the extrusion direction that may be rectangular, circular, tubular or any other two-dimensional shape, and in which the cross-sections of the individual components may be of any two-dimensional shape.
  • the extruded object may then be cut into the desired length and width of the final part.
  • Such a process would be suitable for the production of a planar sandwich geometry consisting of parallel layers of two or more different materials, or a planar sandwich geometry containing grooves or bosses, provided these have a uniform cross-section in the extrusion direction, or a sandwich geometry in which the whole rail pad and/or the individual components are corrugated, or take some other form, provided it or they have a uniform cross-section in the extrusion direction.
  • Other types of external features such as grooves or bosses may be added later by machining or press-molding, press-forming or thermoforming.
  • the external geometry of the whole pad and its elements may be further modified conformally by press-forming or thermoforming using suitable die shapes so as to introduce, for example, one- or two-dimensional corrugations or other shapes as desired.
  • Simple sandwich geometries comprising solid or foamed elements with a uniform cross-section may be produced by successive continuous casting of different reactive pre-cursor materials onto a single- or double-belt apparatus or conveyer. These may then cur into the desired length and width of the final part and subjected to fost-forming operations in the same way as described for the co-extruded objects above.
  • Another alternative or additional method is a mechanical or adhesive assembly process, where preformed solid elements made of different materials, or multiple materials produced using suitable techniques may be assembled by a mechanical interference or snap fit, or using fasteners, or secured using a suitable adhesive.
  • the preformed elements may be molded, extruded, cast, thermoformed or made using any processing technique compatible with the desired form and material.
  • This method is suitable for any geometry in which the preformed elements may be assembled to form the final part or a preform for the final part without modifying their topology, or else in which a suitable cavity has been introduced by a machining operation. It is therefore not suitable, for example, for geometries in which one or more elements are fully encapsulated by a matrix or another element.
  • additional external features such as studs or ribs may either be molded-in or introduced subsequently by machining to the composite rail pad.
  • the whole composite rail pad typically comprises external dimensions in the absence of loading as follows: external width w is in a range of about 100 to 210 mm, particularly preferably in a range of about 120 to 200 mm, for example about 194 mm.
  • the external length I of the said rail pad which extends along the longitudinal direction L of the later track direction, is about 100 to 210 mm, more preferably about 160 to 200 mm, for example about 190 mm.
  • the thickness or height h of the said rail pad is about 5 to 14 mm.
  • the stiffness of the resulting composite rail pad is adjusted according to EN 13481-2-C or EN 13146-9 in such a way that the static vertical stiffness in compression (i.e., along the thickness or height h of the rail pad) varies in the range from 0 to >2000 kN/mm, but preferably in the range 50 to 200 kN/mm.
  • the ratio of the dynamic stiffness to the static stiffness, i.e., the stiffening of the pad at 10 Hz (tested according to EN 13481-2-C or EN 13146-9), may be varied most preferably by the properties and/or special geometries of the at least one core damping elements, or by the use of special geometries of the pad matrix such as external grooves or studs.
  • said sheet may also include external studs or ribs or other types of profile on one or both major faces (i.e., those faces in direct physical contact with either the pad matrix, the sleepers, or the metallic rails).
  • said pad matrix and/or said at least one damping element may also include internal gaps or holes or grooves or other types of profile, either fully encapsulated by the respective material of the pad matrix and/or said at least one damping element or in direct physical contact with either the pad matrix, the sleepers, or the metallic rails.
  • Said gaps or holes or grooves or other types of profile in the said pad matrix and/or said at least one damping element have the advantage of enabling modification of the dynamic stiffness of said pad matrix and/or said at least one damping element without modifying the intrinsic damping properties of said at least one damping element.
  • Gaps contained entirely within the damping elements such as surface grooves in a planar damping element with depths less than the thickness of the damping element are advantageous because they allow the damping element to form a continuous interface with matrix, avoiding local lateral slip at the matrix-damping element interface.
  • said gaps or holes or grooves or other types of profile have the shape of cylinders with a spherical or ellipsoidal cross-section, or prisms with a polygonal cross-section, or grooves with a semispherical or semiellipsoidal or rectangular or triangular cross-section.
  • said grooves have rectilinear trajectories. Gaps in the form of grooves with rectilinear trajectories, e.g., parallel to the rail, are advantageous because they release lateral constraints on the deformation of the rail pad, reducing its overall stiffness and increasing the deformation in the damping elements for a given shape and size of the damping elements and a given vertical load.
  • said grooves have regular or irregular zigzag or curvilinear trajectories.
  • Gaps in the form of grooves with zigzag or curvilinear trajectories are advantageous in that they allow more uniform release of lateral constraints on the deformation of the rail pad in damping elements of different widths and/or with respect to deformations parallel and perpendicular to the rail direction.
  • said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element are either filled with air or with a material different from the one used for the damping element, whose bulk modulus is lower than the bulk modulus of the damping element and/or the pad matrix.
  • Filling said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element with a low bulk modulus material is advantageous because it prevents contamination of the interior of the gaps by dirt, abrasion products or other forms of extraneous matter, which would change their mechanical performance over time, without compromising the ability of the gaps to reduce lateral constraints on the deformation of the rail pad.
  • said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element are filled with a material whose bulk modulus is a least one order of magnitude lower than that of the respective material used for the said pad matrix and/or said at least one damping element.
  • said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element are filled with an elastomeric close- celled or open-celled foam.
  • the at least one damping element is configured as a sheet or film that may also include external studs or ribs or other types of profile on one or both major faces (i.e. those faces in direct physical contact with either the pad matrix, the sleepers, or the metallic rails).
  • the pad matrix may also include internal gaps or holes or grooves or other types of profile, either fully encapsulated by the pad matrix or in direct physical contact with either the pad matrix, the sleepers, or the metallic rails.
  • Fig. 1 shows schematic views of several embodiments of rail pads according to the present invention
  • Fig. 2 shows respective schematic cross-sectional views of the rail pads shown in Fig. 1 as well as additional embodiments of rail pads according to the present invention
  • Fig. 3a shows a Pareto performance plot for several embodiments of rail pads according to the present invention
  • FIG. 3b shows a detail of Figure 3a with data for individual embodiments of rail pads according to the present invention
  • Fig. 4 shows schematic perspective views of several embodiments of rail pad geometries according to the present invention corresponding to Figure 3;
  • Fig. 5a shows a schematic top view of three further embodiments of rail pads according to the present invention.
  • Fig. 5b shows a schematic cross-sectional view of the rail pads illustrated in Fig. 5a along the cross-sectional line A-A depicted therein;
  • Fig. 6a shows a schematic top view of a further embodiment of a rail pad according to the present invention.
  • Fig. 6b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 6a along the cross-sectional line A-A depicted therein;
  • Fig. 7a shows a schematic top view of a further embodiment of a rail pad according to the present invention
  • Fig. 7b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 7a along the cross-sectional line A-A depicted therein;
  • Fig. 8a shows a schematic top view of a further embodiment of a rail pad according to the present invention.
  • Fig. 8b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 8a along the cross-sectional line A-A depicted therein;
  • Fig. 9a shows a schematic top view of a further embodiment of a rail pad according to the present invention.
  • Fig. 9b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 9a along the cross-sectional line A-A depicted therein;
  • Fig. 10a shows a Pareto performance plot for several further embodiments of rail pads according to the present invention.
  • Fig. 10b shows a detail of Figure 10a with data for individual embodiments of rail pads according to the present invention.
  • typical elastic surrounding materials for the rail pad matrix have static moduli and dynamic storage moduli not exceeding 0.1 GPa when measured under uniaxial conditions at room temperature (20-30 C), and dynamic storage moduli not exceeding 0.5 GPa but preferably greater than 1 MPa and tan delta not exceeding 0.2 when measured under uniaxial conditions at room temperature (20-30 °C) and frequencies of up to 10 ⁇ 00 Hz.
  • Suitable materials may include, but are not limited to, semicrystalline or elastomeric materials based on ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU) or polyurethane urea (PUE), crosslinked ethylene-propylene-diene monomer (EPDM) rubber, crosslinked natural (NR) or synthetic cis 1,4- polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene-butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as isotactic polypropylene-vulcanized ethylene-propylene-diene-monomer (EPDM) blends, cop
  • damping refers to the restraint of vibratory motion, which may in turn cause noise, through energy dissipation.
  • a “damping material” is a material with an intrinsic capacity to restrain vibratory motion through energy dissipation, usually in the form of heat. To characterize this capacity, we use the damping factor, tan delta, of the material. In a viscoelastic material, “tan delta” is the ratio of the loss modulus, which determines the rate of energy dissipation during mechanical deformation, to the storage modulus, which determines the amount of mechanical energy stored in the material for a given applied force or deformation.
  • Tan delta may hence be determined from the phase and amplitude of the stress when a material is subjected to a cyclic deformation, for instance by using a disc rheometer under conditions of atmospheric pressure and at the desired temperature and frequency typically chosen to be in the range -150 to 300 °C and 0.01 to 100 Hz, respectively, as known in the art. Tan delta may be determined outside this frequency range at a given temperature from measurements at other temperatures making use of the time- temperature superposition principle, as again known in the art. It is also given by the ratio of the mechanical energy dissipated per radian during a loading cycle to the peak potential energy in the cycle, and is hence often called the "loss factor".
  • maximum dimension refers to those parameters or measurements required to define the shape and/or size, such as height, width, and length, of an object.
  • the maximum dimension of a two-dimensional object such as a rectangle, a polygon, or a circle, is the longest straight-line distance between any two points on the object. Therefore, the maximum dimension of a circle is its diameter; a rectangle its diagonal, and a polygon its longest diagonal.
  • the maximum dimension of a three-dimensional object is the longest straight-line distance between any two points on the object.
  • composite refers to a material made up of different components that are chemically and/or morphologically distinct, and show dissimilar chemical and/or physical properties in the finished structure, distinguishing composites from homogeneous mixtures or solid solutions. Composites may therefore show property profiles that cannot be achieved with the individual components.
  • composite and “multi-material” are used interchangeably in the frame of the present disclosure.
  • foam refers to a substance that is formed by encompassing a plurality of polydisperse or monodisperse gas bubbles, referred to herein as "cells", within a mass of a liquid or a solid, constituting the films of walls separating the cells.
  • the regions occupied by a tangible condensed mass are regarded as the "solid” fraction of the foam, while all other regions not occupied by this fraction are regarded as the "gas" fraction of the foam.
  • the foam is a combination of a polymeric porous solid matrix and gas-filled cells, typically filled with ambient air.
  • porous solid matrix refers to the non-gaseous part of the foam, which contributes substantially to the mass of the foam but substantially less to its volume. Porous materials in general are classified either as “open” or “closed” foams.
  • closed foams have “cells” (pores, voids) where the faces shared with neighboring "cells” are solid membranes; these closed foams entrap the pore fluid, which cannot easily escape through the solid membranes delimiting the "cells”.
  • Classical open foams have no membranes between neighboring cells, but only struts along the edges where three or more cells meet. Such open foams naturally have a fully interconnected pore space, and a fibrous network of solid material.
  • the polymeric foam composition presented herein is characterized by a density (p) that ranges from 0.01 to 2 grams per centimeter cubed, such as from 0.05 to 0.9 grams per centimeter cubed.
  • Fig. 1 shows a schematic illustration of several embodiments of a multimaterials rail pad 10, lOa-f according to the present invention, namely: la) a rail pad 10a with matrix la comprising a single centred cuboid damping element 2a, lb) a rail pad 10b with matrix lb comprising four cuboid damping elements 2b, lc) a rail pad 10c with matrix lc comprising a single centred cylindrical damping element 2c,
  • the multi-material rail pads 10, lOa-f comprises the pad matrix 1, la-f comprising or consisting of a first material and the at least one damping element 2, 2a-f at least partially encapsulated or embedded in the pad matrix 1, la-f, said damping element(s) 2, 2a-f comprising or consisting of a second material, wherein the second material of the at least one damping element 2, 2a-f has a damping factor tan delta > 0.5 at a frequency of 1000 Hz.
  • Fig. 2 shows possible schematic cross-sectional views of the embodiments of rail pad lOa-f according to the present invention shown in Fig. la and alternative versions and/or further embodiments lOg, lOh, lOi thereof in parallel to the rail direction at mid-point of the rail pad (matrix 1, damping element(s) 2, stiffness modifying elements 3).
  • the damping elements 2, 2a-i may have the following dimensions, forms and/or shapes: a. single centred cuboid damping element of thickness less than overall rail pad thickness (cf. Figure 3b points j-n,p)), b. multiple cuboid damping element of thickness less than overall rail pad thickness (cf. Figure 3b point o)), c.
  • single centred cuboid damping element of thickness equal to overall rail pad thickness (cf. Figure 3b point q)), d. multiple cuboid damping elements of thickness equal to overall rail pad thickness (cf. Figure 3b points r,s)), e. single centred corrugated cuboid damping element of thickness less than overall rail pad thickness (cf. Figure 3b points t-v)), f. single centred cuboid damping element of thickness less than overall rail pad thickness + surface grooves to modify stiffness, g. single centred cuboid damping element of thickness less than overall rail pad thickness + surface studs to modify stiffness, h.
  • Fig. 3a shows a schematic Pareto performance plot for multimaterials rail pads based on an ethylene vinyl acetate (EVA) matrix containing modified polyisobutylene (PIB) damping elements: the tangent delta and stiffness values are for the compression of the whole of the rail pad between two rigid plates in each case:
  • EVA ethylene vinyl acetate
  • PIB modified polyisobutylene
  • the multi-material rail pads can be grouped into three groups: (A) rail pads 10 according to the present invention with improved acoustic performance and improved or maintained superstructure protection performance, compared to a reference rail pad made from EVA; (B) rail pads according to the present invention with improved superstructure protection performance and improved or maintained acoustic performance, compared to a reference rail pad made from EVA; (C) multi-material rail pads 10 with inferior acoustic and/or superstructure protection performance (counter examples)
  • Fig. 4 shows the geometries of the rail pads lOj-v that correspond to the numbers in the Pareto diagram shown in Fig. 3b, partially including sheets or film 11.
  • one or more optional air gaps may be introduced according to further embodiments of the present invention.
  • Fig. 5a shows a schematic top view of a further embodiment of a rail pad 10, 10a according to the present invention.
  • the rail pad 10a has a static stiffness of 477 kN/mm, tan delta at l'OOO Hz of 0.63, PIB content of 60 vol%, and further comprises four grooves 5 running along the top side essentially in parallel to each other as well as to a rail direction R of a rail (not shown).
  • the grooves 5 have a groove width W5 of, e.g., 5 mm, and a groove depth ts of, e.g., 2 mm.
  • the two inner grooves 5 are arranged at a first distance di from each other of, e.g., 72 mm measured essentially in a direction perpendicular to the rail direction R.
  • the two outer grooves 5 are arranged at an edge of the core damping element 2 adjacent to an outer rim of the pad matrix 1 of the rail pad 10a.
  • the two outer rims of the rail pad 10a are arranged at a second distance of 140 mm from each other measured essentially in a direction perpendicular to the rail direction R.
  • a further embodiment of a rail pad 10, 10b according to the present invention has a static stiffness of 508 kN/mm, tan delta at 1 ⁇ 00 Hz of 0.44, and a PIB content of 45 vol%, again with a groove width of 5 mm as well as corresponding distances di and dn.
  • Fig. 5b shows a schematic cross-sectional view of the rail pads 10a, b,g illustrated in Fig.
  • the gooves 5 have a groove depth ts measured in the height direction of the rail pad 10a, b,g.
  • the rail pads 10a, b each comprise grooves 5 having a groove depths of 2 mm, while the rail pad 10g has a groove depth of 4 mm.
  • Figs. 6a and 6b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10d according to the present invention comprising four grooves 5.
  • the rail padl06 has a static stiffness of 293 kN/mm, tan delta at l'OOO Hz of 0.66, and PIB content of 60 vol%.
  • the grooves 5 have a groove width ws of 5 mm, and a groove depth of 2 mm.
  • the two inner grooves 5 are arranged at a first distance d5i from each other of, e.g., 40 mm, and the outer edges of the two outer grooves 5 are arranged at a second distance d5 2 of, e.g., 109 mm from each other, both measured essentially in a direction perpendicular to the rail direction R.
  • Figs. 7a and 7b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10e according to the present invention comprising two grooves 5 crossing each other in the center of the rail pad 10e as they extend diagonally between corners of the rail pad 10e diametrally opposing each other.
  • the rail pad 10e has a static stiffness of 362 kN/mm, tan delta at 1 ⁇ 00 Hz of 0.58, and a PIB content of 60 vol%, while the grooves have a groove width Ws of 5 mm, and a groove depth t2 of 2 mm.
  • Figs. 8a and 8b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10z according to the present invention comprising two grooves 5 extending along the top of the rail pad 10z along the rail direction R and describing a serpentine line or sine wave with a length of a quarter cycle TT/2 of 17.5 mm measured essentially in parallel to the rail direction R.
  • the grooves 5 are formed mirror symmetrically to each other with respect of a center line of the rail pad 10z extending along the rail direction R.
  • the grooves have a groove width ws of 5 mm, a groove depth of 2 mm, and are distanced from the outer rim of the rail pad lOz by a mean first distance dZi of 35mm while the second distance d 2 bettween the outer rims of the rail pad 10z again amounts to 140 mm.
  • Figs. 9a and 9b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10h according to the present invention.
  • the rail pad 10h has a static stiffness of 322 kN/mm, tan delta at l'OOO Hz of 0.59, and a PIB content of 60 vol%, and further comprises four grooves 5 running along the top side essentially in parallel to each other as well as to the rail direction R which are each filled with stiffness modifying elements 3 as inserts formed of PU foam.
  • the two inner stiffness modifying elements 3 are arranged at the first distance di from each other of, e.g., 72 mm measured essentially in a direction perpendicular to the rail direction R.
  • the two outer stiffness modifying elements 3 are arranged at the edge of the core damping element 2 adjacent to the outer rim of the pad matrix 1 of the rail pad 10h.
  • the two outer rims of the rail pad 10 h are arranged at the second distance of 140 mm from each other measured essentially in a direction perpendicular to the rail direction R.
  • Fig. 10a shows a schematic Pareto performance plot for multimaterials rail pads 10, 10a-h based on an ethylene vinyl acetate (EVA) matrix containing modified polyisobutylene (PIB) damping elements: the tangent delta and stiffness values are for the compression of the whole of the rail pad 10a-h between two rigid plates in each case.
  • Fig. 10b shows a detail of Figure 10a including rail pads 10, lOa-v corresponding to those shown in Figs. 3a and 3b, and in addition rail pads 10, 10a-h.
  • EVA ethylene vinyl acetate
  • PIB modified polyisobutylene
  • the multi-material rail pads lOa-v can again be grouped into three groups: (A) rail pads according to the present invention with improved acoustic performance and improved or maintained superstructure protection performance, compared to a reference rail pad made from EVA; (B) rail pads according to the present invention with improved superstructure protection performance and improved or maintained acoustic performance, compared to a reference rail pad made from EVA; (C) rail pads 10 with inferior acoustic and/or superstructure protection performance (counter examples).
  • Rail pads 10a-h can be grouped into a fourth group (D), which contains multimaterials rail pads according to the present invention containing air gaps or compressible foam inserts with improved acoustic performance and improved or maintained superstructure protection performance, compared to a reference rail pad made from EVA.
  • D fourth group
  • rail pads from group (D) in general show improved acoustic performance over rail pads from group (B) with comparable superstructure protection performance, because the release of lateral constraints in the damping elements 2a-h due to the stiffness modifying elements 3 and/or grooves 5 increases damping performance, and improved superstructure performance over rail pads from group (A) with comparable acoustic performance, because the release of lateral contraints due to the stiffness modifying elements 3 and/or grooves 5 reduces the overall stiffness of the railpad.
  • Group A contains examples of rail pads 10 according to the present invention with significantly improved acoustic performance and maintained or improved superstructure performance in comparison with the prior art.
  • Rail pads 10j,k,o,p,u,t,v represent designs examples which typically are rich in damping material and do not comprise any grooves.
  • Group B contains rail pads 10 as examples with significantly improved superstructure performance and maintained or improved acoustic performance in comparison with the priort art.
  • Rail pads 2l,m,n represent design examples containing less damping material than rail pads 10j,k,o,p,u,t,v and neither comprise any grooves.
  • group C contains some reference examples of relatively low performance.
  • Group D contains examples of rail pads 10a-h according to the present invention with significantly improved acoustic and superstructure performance in comparison to the prior art and having varying amounts of damping material (based on designs in groups A or B) and grooves.
  • the material of the at least one damping element 2, 2a-v, 2a-h may have a damping factor tan delta > 0.65 at a frequency of 1000 Hz.
  • the material of the at least one damping element 2, 2a-v, 2a-h may have a damping factor tan delta > 0.8 at a frequency of 1000 Hz.
  • the material of choice shows significant damping over a significant portion of the audible frequency range, namely a tan delta > 0.5 for audible frequencies > 200 Hz, and/or tan delta > 0.8 for audible frequencies > 1000 Hz. All of these values refer to the intrinsic tan delta of the second, damping material of the damping element 2a-v, 2a-h at room temperature.
  • the rail pad 10, lOa-v, 10a-h has an overall plate-like geometry suitable for insertion between a rail and a railway sleeper and have lengths I, widths w, and heights h, that are standardized. (Other geometries are possible as required by the railway superstructure.)
  • the multi-material rail pads 10, lOa-v, 10a-h are at least formed of a pad matrix la-v, la-h and at least one damping element 2a-v (see Figs. 1, 2, 4, and 5a to 9b).
  • the damping element 2a-v, 2a-h is preferably formed and arranged such that it is fully encapsulated and its center of mass lies in the mid-plane of the rail pad or, alternatively such that its top surface lies flush with the top surface of the rail pad 10, lOa-v, 10a-h such that the damping element 2a-v is touching the rail. This latter arrangement may, for example, facilitate fabrication.
  • the multi-material rail pads 10 a-v may contain at least one additional stiffness-modifying element 3a-v.
  • the pad matrix la-v, la-h of the composite rail pad 10, lOa-v, 10a-h, is made of a resilient elastic material forming the body of the composite rail pad 10, lOa-v, 10a-h.
  • the main role of the pad matrix la-v, la-h is to mechanically decouple the rail from the sleeper.
  • the compression modulus of the pad matrix la-v, la-h should be chosen to ensure that the global static compression and shear stiffness requirements of the composite rail pad 10, lOa-v, 10a-h are met, depending on the elastic properties of the damping elements, depending on whether a "hard” (nominal throughthickness compressional stiffnesses in the range 200 to as much as 1'300 kN/mm) or "soft” (nominal through-thickness compressional stiffnesses in the range 30 kN/mm to 150 kN/mm) rail pad 10, lOa-v, 10a-h is desired.
  • the requirements of the European norm 13146 are followed and implemented in the rail pad 10, lOa-v, 10a-h of the invention.
  • the pad matrix 1 should also preferably meet certain requirements for environmental and weathering resistance and temperature stability according to the needs and circumstances (for instance, the country in which it is used), and show adequate resilience, fatigue resistance, abrasion resistance and creep resistance: for example, a rail pad 10, lOa-v, 10a-h according to the present invention should not show permanent deformation on the time-scale of train pass-by or as a result of the related clamping force.
  • the pad matrix 1 may be prepared from an elastic material or a combination of elastic materials. It may be made from a single thermoplastic or thermoset or elastomeric material, including but not limited to crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene-propylene-diene monomer (EPDM) rubber or natural rubber (NR), which are already known and validated as suitable materials for rail pad manufacturing, and also synthetic cis 1,4-polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene- butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as iso
  • thermoplastic or thermoset or elastomeric materials and their composites may optionally contain microscopic or macroscopic voids, pores and/or gaps.
  • the pad matrix 1 may additionally or alternatively by prepared from two or more of the porous or non-porous single thermoplastic or thermoset or elastomeric materials or their composites.
  • the pores or gaps may be designed and/or distributed across the pad matrix 1 to reduce the final stiffness, not only by substituting part of the matrix with air, but also by increasing the compressibility of the material, so that it can deform more easily when confined between a rail and a sleeper.
  • the pad matrix 1 of the invention may comprise or consist of a closed-cell or open-cell foam, preferably a closed-cell foam with a pore density of not more than around 30%, e.g., a pore density comprised between 1 and 10%, between 1 and 20% or between 1 and 30%.
  • the rail pad 10, lOa-v, 10a-h one or more damping element(s) 2, 2a-v, 2a-h are introduced.
  • the main role of these one or more damping element(s) 2, 2a-v, 2a-h is to improve noise reduction and vibration damping without degrading the function of the rail pad to decouple the rails and sleepers mechanically.
  • the rail pad 10, lOa-v, 10a-h according to the invention comprises a single damping element 2.
  • the rail pad 10, lOa-v, 10a-h according to the invention comprises plurality of damping elements 2.
  • the one or more damping element(s) 2, 2a-v, 2a-h are prepared from a damping material. It has been found that the damping material for the one or more damping element(s) 2, 2a-v, 2a-h should have a damping factor tan delta > 0.5 at a frequency of 1000 Hz.
  • the material of the at least one damping element 2, 2a-v, 2a-h may have a damping factor tan delta > 0.65 at a frequency of 1000 Hz. equal to or greater than 0.5 at a frequency of 1000 Hz, particularly at 21 °C, such as a tan delta > 0.65 or > 0.8.
  • the used materials also shows tan delta ranging from about 0.6 to 1.2 in the audible frequency range between 100 and 10 ⁇ 00 Hz, at room temperature.
  • the one or more damping element(s) 2, 2a-v, 2a-h can be prepared from a damping material, which is a thermoplastic or thermoset or elastomeric material with a dynamic modulus in the range 1-0.2 GPa and preferably in the range 10 MPa-0.2 GPa at l'OOO Hz and room temperature, selected from a non-limiting list comprising polyisobutylene (PIB), crosslinked polyisobutylene (butyl rubber, IIB), polyurethane elastomers (PU), polymer-modified bitumen, polar polymers, such as nitrile, hydrogenated or carboxylated nitrile rubber (NBR, HNBR, XNBR), chlorinated polyolefins (for example, polychloroprene (CR), chlorinated polyethylene or polypropylene, or chlorosulphonated polyethylene), acrylate rubbers (ACM) or epoxidized rubbers (ER), particularly where these have been modified with polar
  • thermoplastic or thermoset or elastomeric materials and their composites may optionally contain microscopic or macroscopic pores or gaps, which may be introduced directly into at least one damping element 2,2a-v, 2a-h, for example, by molding or using a suitable porogen, or via pre-formed second phase inclusions such as polymer foam beads.
  • the at least one damping element 2, 2a-v, 2a-h may constitute between 10 and 90% of the total volume of the rail pad 10, lOa-v, 10a-h, such as for instance between 15 and 60% of the total volume of the rail pad 10, lOa-v, 10a-h, between 15 and 30% of the total volume of the rail pad 10, lOa-v, 10a-h, between 30 and 70% of the total volume of the rail pad 10, lOa-v, 10a-h or between 40 and 80% of the total volume of the rail pad 10, lOa-v, 10a-h.
  • the one or more damping element(s) 2, 2a-v, 2a-h may be incorporated into the rail pad 10, lOa-v, 10a-h in different ways.
  • the one or more damping element(s) 2, 2a-v, 2a-h may be incorporated into the rail pad 10, lOa-v, 10a-h in the form of one or more macroscoic units with defined geometries that comprise or consist of the damping materials listed above.
  • the one or more damping element(s) 2, 2a-v, 2a-h may adopt any geometrical form including, but not limited to forms with a constant or varying polygonal, circular or elliptical cross-section, such as spheres, ellipsoids, cylinders, or prisms with a polygonal, elliptical, or circular base. If two or more damping elements 2, 2a-v, 2a-h are introduced, they may have the same or different geometrical forms.
  • the one or more damping element(s) 2, 2a-v, 2a-h may span the whole height, or the whole width, or the whole length of the rail pad 10, lOa-v, 10a-h, or it may be entirely encapsulated/embedded by the pad matrix 1 and/or by the optional stiffness-modifying element(s) 3 on the top and/or bottom and/or either side and/or the top and/or the bottom of the rail pad 10, lOa-v, 10a-h.
  • the at least one damping element 2, 2a-v, 2a-h is configured as a sheet or film, that may comprise at least one corrugated surface.
  • the one or more damping element(s) 2, 2a-v, 2a-h may comprise the damping materials listed above in the form of a dispersion of microscopic or macroscopic damping particles in the matrix material, also referred to herein as "particle-like units".
  • the damping particles may be monodisperse (that is, they all have the same size and shape) or polydisperse (that is, they have a distribution of sizes and shapes).
  • Said plurality of monodisperse or polydisperse particle-like units have preferably a maximum dimension or an average dimension comprised between 50 nanometers and 1 millimeter. They may have regular shapes, such as ellipsoids or spheres, or be irregularly shaped (their concentration per unit volume varies depending on the location within the pad matrix 1).
  • the one or more damping element(s) 2, 2a-v, 2a-h that comprise said plurality of monodisperse or polydisperse particle-like units of the damping materials may again have a macroscopic shape with defined geometries. It may adopt any geometrical form including, but not limited to forms with a constant or varying polygonal, circular or elliptical cross-section, such as spheres, ellipsoids, cylinders, or prisms with a polygonal, elliptical, or circular base. If two or more regions of higher concentration of damping particles are present, they may have the same or different geometrical forms.
  • the rail pad 10, 10a- v, 10a-h may span the whole height, or the whole width, or the whole length of the rail pad 10, 10a- v, 10a-h, or they may be encapsulated/embedded by the pad matrix 1 and/or the optional reinforcing element 3 on the top and/or bottom and/or either side and/or the top and/or the bottom of the rail pad 10, lOa-v, 10a-h.
  • the damping materials and their composites may optionally contain microscopic or macroscopic void, pores and/or gaps.
  • the damping element(s) 2, 2a-v, 2a-h may also comprise or consist of a foam, such as close-celled or open-celled foams with a pore density of not more than around 30%, e.g., a pore density comprised between 1 and 10%, between 1 and 20% or between 1 and 30%.
  • the geometry and placement of the one or more damping element(s) 2, 2a-v, 2a-h and the spatial distribution of the optional two or more damping elements 2, 2a-v, 2a-h are tailored in order to ensure long term mechanical stability, while favoring damping of deformation modes of the rails during train pass-by that are associated with noise generation, such as pin-pin vertical flexural modes in the audible frequency range.
  • the rail pad 10, lOa-v, 10a-h may have a core-shell morphology comprising a hard elastic matrix 1 fully encapsulating a centered cuboid damping element 2, wherein said damping element 2, 2a-v, 2a- h constitutes between 15 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h.
  • the rail pad 10, lOa-v, 10a-h may have a core-shell morphology comprising a hard elastic matrix 1 fully encapsulating a centered cuboid damping element 2, wherein said damping element 2, 2a-v, 2a-h constitutes between 30 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h.
  • the rail pad 10, lOa-v, 10a-h may have a core-shell morphology with a hard elastic matrix 1 fully encapsulating a centered corrugated cuboid damping element 2, wherein said damping element 2, 2a-v, 2a-h constitutes between 15 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h.
  • the rail pad 10, lOa-v, 10a-h may have a core-shell morphology with a hard elastic matrix 1 fully encapsulating a corrugated centered cuboid damping element 2, wherein said damping element 2, 2a-v, 2a- h constitutes between 30 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h.
  • the obtained rail pad 10, lOa-v, 10a-h shows optimized acoustic performances (i.e., reduction of airborne noise at audible frequencies between 200 to about 2000 Hz), and better track protection performances than a reference material (EVA) typically used in rail pads.
  • the obtained rail pads 10, lOa-v, 10a-h have a static stiffness in the range of 500-1000 kN/mm, tan delta (of the pad) between 0.3 and 0.6 at 1000 Hz, and a damping material (e.g., PIB) content between 15 and 50%.
  • the obtained pads 10, lOa-v, 10a-h have a static stiffness in the range of 700-1000 (e.g., between 800 and 900) kN/mm, tan delta (of the pad) between 0.3 and 0.5 (e.g., between 0.3 and 0.4), and a damping material (e.g., PIB) content between 15 and 20%.
  • a damping material e.g., PIB
  • the obtained rail pad 10, lOa-v, 10a-h shows optimized track protection performances, and better or similar acoustic performance than a reference material (EVA) typically used in rail pads known from the prior art.
  • the obtained rail pads 10, lOa-v, 10a-h have a static stiffness in the range of 300-800 kN/mm, tan delta (of the pad) between 0.2 and 0.7 at 1000 Hz, and a damping material (e.g., PIB) content between 30 and 70%.
  • the obtained pads 10, lOa-v, 10a-h have a static stiffness between 250 and 500 (preferably between 300 and 400) kN/mm, tan delta (of the rail pad 10) between 0.4 and 0.8 (preferably between 0.6 and 0.8), and a damping material (e.g., PIB) content between 40 and 80%.
  • a damping material e.g., PIB
  • one or more optional stiffness-modifying element(s) 3 may be introduced.
  • the main role of the one or more optional stiffness-modifying element(s) 3 is to tailor the local mechanical stiffness of at least portion of the pad matrix 1. It is placed in specific locations within or onto the pad matrix 1 as required to increase or decrease its stiffness locally with respect to specific modes of mechanical solicitation.
  • the one or more stiffness-modifying element 3 may separate at least two damping elements 2.
  • the at least one optional stiffness-modifying element 3 should also meet standard requirements for environmental and weathering resistance and temperature stability and show adequate resilience, fatigue resistance, abrasion resistance and creep resistance over the whole range of service conditions.
  • the at least one stiffnessmodifying element 3 is preferably separated from the at least one damping element 2.
  • the one or more optional stiffness-modifying element(s) 3 can be used as rigidifying elements.
  • the compression modulus and shear stiffness of the one or more optional stiffness-modifying element(s) 3 are chosen to be equal to, or higher than, those of the pad matrix 1.
  • the stiffness-modifying element(s) 3 comprises or consists of a material that increases the stiffness of at least a portion of the pad matrix 1, relative to the stiffness of the pad matrix 1 itself, thereby rigidifying at least a portion of the rail pad.
  • the one or more optional stiffness-modifying element(s) 3 may be prepared from an elastic material or a combination of materials. It may be made from a single thermoplastic or thermoset or elastomeric material, including but not limited to crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene-propylene-diene monomer (EPDM) rubber, or crosslinked natural rubber (NR) or any other organic or inorganic material, such as a metal, provided that the said material have one more elastic moduli different from those of the matrix material.
  • EVA crosslinked or non-crosslinked ethylene vinyl acetate
  • HDPE high density polyethylene
  • PU polyurethane
  • EPDM crosslinked ethylene-propylene-diene monomer
  • NR crosslinked natural rubber
  • These materials may be processed into composites that may contain additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica
  • the one or more optional stiffnessmodifying element(s) 3 are used as softening elements. Their compression modulus and shear stiffness of the one or more optional stiffness-modifying element(s) 3 are chosen to be equal to, or lower than, those of the pad matrix 1. Accordingly, the stiffness-modifying element(s) 3 comprises or consists of a material that decreases the stiffness of at least a portion of the pad matrix 1, relative to the stiffness of the pad matrix 1 itself, thereby softening at least a portion of the rail pad 10, lOa-v, 10a-h.
  • the one or more optional stiffness-modifying element(s) 3 to be used as softening elements may be prepared from a single thermoplastic or thermoset or elastomeric material, including but not limited to crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene- propylene-diene monomer (EPDM) rubber, or crosslinked natural rubber (NR), a compressible elastic material such as a material containing macroscopic cavities, including naturally occurring porous materials such as cork, or an elastomeric foam, including but not limited to a polyurethane (PU) foam, crosslinked ethylene-propylene- diene monomer (EPDM) rubber foam or crosslinked natural rubber (NR) foam, provided that the said material have one or more elastic moduli (i.e. bulk modulus, shear modulus and tensile modulus, or a multiplicity of moduli in the case of an isotropic material) lower than those of the matrix material.
  • EVA cross
  • the rail pad 10, lOa-v, 10a-h may comprise one or more optional stiffness-modifying element(s) 3 that combine the materials listed for the rigidifying and the softening elements.
  • the rail pad 10, lOa-v, 10a- h may comprise one or more optional stiffness-modifying element(s) 3 that are used as rigidifying elements as well as one or more optional stiffness-modifying element(s) 3 that are used as softening elements.
  • the rail pad 10, lOa-v, 10a-h comprising the pad matrix 1 and the at least one damping element 2, 2a-v, 2a-h and the at least one optional reinforcing element 3 is preferably prepared by methods known in the art such as (plastic) extrusion, compression molding, resin transfer molding or injection molding method or reactive extrusion, reactive compression molding, reactive resin transfer molding or reactive injection molding, if required in the presence of a chemical or physical porogen but may also be prepared by casting, or certain individual components may be pre-formed by casting, extrusion, compression molding, resin transfer molding, injection molding, calendering, thermoforming or additive manufacture, or reactive extrusion, reactive compression molding, reactive resin transfer molding, reactive injection molding or reactive casting, if required in the presence of a chemical or physical porogen, or any other suitable technique for solid or porous thermoplastic or elastomeric parts, and subsequently combined with the other components in a multi-step molding procedure such as compression molding, or over-injection molding or with a film stacking procedure combined if required
  • damping elements 2, 2a-v, 2a-h are preferred by extrusion, injection molding, compression molding or any other suitable process, incorporating crosslinking and/or a porogen if required, the subsequent introduction of the damping elements 2, 2a- v, 2a-h into a mold cavity and subsequent overmolding with the material constituting pad matrix 1.
  • the at least one reinforcing element 3 is preformed by extrusion, injection molding, compression molding or any other suitable process, incorporating crosslinking and/or a porogen if required, subsequently introduced into a mold cavity together with the damping elements 2, and subsequently overmolded with the material constituting pad matrix 1. Additional external features such as studs or ribs may either be molded-in or introduced subsequently by machining to the composite rail pad 10, lOa-v, 10a-h.
  • the whole composite rail pad 10, lOa-v, 10a-h typically comprises external dimensions in the absence of loading as follows: external width w is in a range of about 100 to 210 mm, particularly preferably in a range of about 120 to 200 mm, for example about 194 mm.
  • the external length I of the said rail pad 10, lOa-v, 10a-h, which extends along the longitudinal direction L of the later track direction, is about 100 to 210 mm, more preferably about 160 to 200 mm, for example about 190 mm.
  • the thickness or height h of the said rail pad 10, 10a- v, 10a-h is about 5 to 14 mm.
  • the stiffness of the resulting composite rail pad 10, lOa-v, 10a-h is adjusted according to EN 13481-2-C or EN 13146-9 in such a way that the static vertical stiffness in compression (i.e. along the thickness or height h of the rail pad 10, lOa-v, 10a-h) varies in the range from 0 to >2000 kN/mm, but preferably in the range 50 to 200 kN/mm.
  • the ratio of the dynamic stiffness to the static stiffness i.e.
  • the stiffening of the pad at 10 Hz may be varied most preferably by the properties and/or special geometries of the at least one core damping elements 2, or by the use of special geometries of the pad matrix 1 such as external grooves or studs.
  • the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at 000 Hz ⁇ 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 1000 kN/mm, adjusted if necessary using external or internal voids or grooves, and the overall tang
  • the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz ⁇ 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 30 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 700 kN/mm, adjusted if necessary using external or internal voids or grooves, and
  • the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz ⁇ 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 50 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 500 kN/mm, adjusted if necessary using external or internal voids or grooves, and
  • the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz ⁇ 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered corrugated cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 500 kN/mm, adjusted if necessary using external or internal voids or groove
  • the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz ⁇ 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa partially encapsulating a cuboid damping element 2 centered in the horizontal plane such that either or both of the top or bottom surfaces of the damping element 2 are flush with the top or bottom surfaces of the rail pad 10, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C
  • the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz ⁇ 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, or partially encapsulating a cuboid damping element 2 centered in the horizontal plane such that either or both of the top or bottom surfaces of the damping element 2 are flush with the top or bottom surfaces of the rail pad 10, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with
  • Materials data density >0.92 g/cc, glass transition temperature -30 to -40 °C, tensile strength 10-30 MPa, elongation at break 700 %, static Young's modulus (measured at 10 mm/min) 2.3 MPa.

Abstract

The invention relates to a rail pad (10, lOa-v, 10α-η) comprising: a) a pad matrix (1) comprising a first material and b) at least one damping element (2) at least partially encapsulated or embedded in the pad matrix (1), said damping element (2) comprising or consisting of a second material, wherein the second material of the at least one damping element (2) has a damping factor tan delta > 0.5 in the audible frequency of 1000 Hz. Methods for producing the rail pad of the invention are also disclosed.

Description

MULTI-MATERIAL RAIL PAD AND METHOD FOR
MANUFACTURING SAME
TECHNICAL FIELD The present invention pertains to the field of material science and engineering. In particular, the invention relates to a multi-material rail pad having improved mechanical and/or acoustic features.
STATE OF THE ART Rail pads are known from the prior art as compliant (low stiffness) elastic sheets typically made of a polymer-based material that are inserted between the rails and sleepers as part of a rail fastening system.
The primary function of elastic rail pads is to protect the sleepers from transient static and dynamic loads due to passing trains without compromising the mechanical stability of the ensemble of the track. The presence of compliant layers between the rails and the sleepers ensures uniform loading over the whole of the rail-sleeper contact area, thus avoiding locally high stress concentrations that may result in damage to the sleepers.
Furthermore, by mechanically decoupling the rails from the rigid sleepers, compliant elastic rail pads allow the rails to bend more freely than when such rail pads are absent, so that the loads due to passing trains are more evenly distributed over the ensemble of the sleepers. This not only further reduces the maximum transient loads on the sleepers but also reduces the maximum loads on the ballast and substructure, which in turn reduces degradation of the ballast and substructure, and the rate of settlement of the ballast, and hence the frequency with which the track needs to be maintained. However, the increased freedom of the rails to bend also allows them to vibrate more freely in response to load fluctuations whose frequency is in the audible frequency range, which arise mainly from irregularities in the metallic wheel-rail interface. This leads to significant increases in rail vibration and hence radiation of airborne noise when a train passes over a track equipped with compliant elastic rail pads, with highly undesirable consequences for the environment.
Commercial rail pads are nowadays made of single resilient elastic or single elastomeric materials such as ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene- propylene-diene monomer (EPDM) rubber or natural rubber (NR).
A typical rail pad is plate-shaped but may also include internal porosity or external studs or ribs or other types of profile on one or both major faces (i.e., those faces in direct physical contact with the sleepers and the metallic rails), that serve to better distribute the load on the pad and reduce abrasion, as known from EP2990529. The thickness of rail pads in the trade typically varies from 4 to 15 mm in the unloaded state, but their effective thickness in service in the absence of additional loading by a train is determined by its stiffness and clamping load, which is typically from 7.5 to more than 20 kN depending on the fastening system. The horizontal dimensions of the rail pad are chosen according to the track geometry. For example, rail pads for use with UIC54 rail profiles are 180 mm long and 140 mm wide, while for UIC60 rails the rail pads are 180 mm long and 148 mm wide.
The rail pad material, additives and geometry are chosen according to the desired vertical and lateral stiffness in compression and shear under static and dynamic loading, which depend in turn on the type of fastener used to fix the rail to the sleeper and the intended type of rail traffic. Regardless of how they perform with respect to noise, rail pads must have lower stiffness than the rails and sleepers, and must show reproducible and substantially reversible behaviour with respect to large quasi-static and impact loads if they are to fulfil their primary function, namely protection of the superstructure of a ballasted railway track from repeated deformation due to axle loads, which are typically up to 22.5 tonnes in Europe, corresponding to a maximum static or quasi-static force of roughly 110 kN per bogie (set of wheels).
Rail pads must also provide a stable support to the train in straight and curved track sections and, in addition to meeting basic static mechanical property requirements, show adequate resistance to creep and fatigue, long term abrasion, moisture, ozone, UV radiation, hydrocarbons and other railway-related chemicals over an extended continuous use period at temperatures between about -20 and 60 °C.
The stiffness of the rail pad may then be selected by choosing a material with the appropriate elastic response from the wide range of polymer-based materials that meet the basic design requirements. Because stiffness is determinant for their primary function, rail pads are classified as either "hard" (nominal through-thickness compressional stiffnesses in the range of 200 to as much as 1'300 kN/mm) or "soft" (nominal through-thickness compressional stiffnesses in the range of 30 kN/mm to 150 kN/mm), hard rail pads generally being considered to provide less efficient protection to the track superstructure than soft rail pads.
The effective stiffness for a given material may be modified by adjusting the rail pad geometry, prevalent industrial design strategies including the use of studs or ribs on its major faces and/or controlled internal porosity, which serve to reduce the constraints on lateral expansion due to friction with the rigid substrates. Manufacturers of soft rail pads also exploit porosity to reduce the effective loading area of the matrix and hence vary the rail pad stiffness at constant thickness without the need to modify other matrix properties. Both porosity and external profiles also provide a means of engineering the non-linear response of the rail pad. A rail pad may hence be designed to show a soft static response to small deformations, but a higher effective stiffness and hence a harder response as the deformation increases.
According to the state of the art, rail pad materials are chosen primarily for their elastic properties and mechanical and dimensional stability. Most common materials show no major thermomechanical transitions in the range of frequencies, loads, and temperatures of relevance to rail pad operation, which offers the advantage of a uniform elastic response over a wide range of service conditions.
Conventionally, prior art rail pads are optimized with respect to elasticity, stiffness, and durability, so that they provide the desired levels of sleeper and ballast protection over long periods of time. According to the state of the art, high stiffness, hard rail pads with compressional stiffness in the direction perpendicular to the plane of the rail pad k > 250 kN/mm, which limit the freedom of the rails to bend, are preferred for limiting airborne noise, while low stiffness, soft rail pads with compressional stiffness in the direction perpendicular to the plane of the rail pad k < 120 kN/mm, which provide greater decoupling of the rails and the sleepers and improve sleeper and ballast protection, lead to increased noise. According to the state of the art, simultaneous optimization for noise reduction and superstructure protection is not possible.
In many other applications, noise and vibration damping, that is, the restraint of vibratory motion (which may in turn cause noise) through energy dissipation, may be promoted through use of materials that show strong intrinsic damping, including many highly viscoelastic polymers.
However, the use of viscoelastic polymers and polymer-based composites that show strong frequency-dependent stiffness and strong intrinsic damping, as reflected by a damping coefficient tan delta > 0.5 in the frequency range where rail vibrations contribute significantly to noise, has not previously been reported. Indeed, highly viscoelastic polymers with damping coefficients tan delta > 0.5 are commonly considered unsuitable for rail pads because they are associated with poor resilience, that is their ability to recover rapidly and completely their original shape after a large deformation, and poor resistance to high cycle fatigue and/or long term creep, which refers to deformation over extended periods of time under sustained loads such as those imposed by the rail clamping system.
Composite rail pads consisting of resin-bonded rubber or cork-PU layered structures have been described in the literature, but these materials are not described to show strong intrinsic damping or strongly frequency-dependent stiffness (Maes, J., Sol, H. and Guillaume, P. 2006. Measurement of the dynamic rail pad properties. Journal of Sound and Vibration. 293, 557-565), and do not solve the problem of the conflicting stiffness requirements for noise mitigation and superstructure protection.
In EP3452659, the ratio of the static stiffness to the dynamic stiffness under load is optimized by a special form of the plate-shaped rail pad, as defined in the relevant test standards EN 13481-2-C and EN 13146- 9. In EP3452659, the rail pad comprises ribs and/or crossbar elements with a different stiffness to the bulk of the rail pad, but these elements are not stated to show strong intrinsic damping or strongly frequency dependent stiffness.
A rail pad made from a single (unspecified) material with surface grooves with a vertical static stiffness of the order of 200 kN/mm and high damping at frequencies above 200 Hz has been described by Prose AG in "Akustisch optimierte Schienenzwischenlage Schlussbericht", 17.111.00 - BAFU Entwicklung Zwischenlage, document No. 04-03-02153, revision 0.00, issued 28 August 2020 (https ://www.aramis. admin. ch/Default?DocumentID=66748&Load=tru e). Noise reduction with respect to a „soft" rail pad (static stiffness 100 kN/mm. These results, however, are comparable to noise levels of a standard hard rail pad made from a material such as EVA with a static stiffness of about 800 kN/mm, as shown in field tests. No improvement of superstructure protection has been reported.
A rail pad with a static stiffness of 60 kN/mm made entirely from ethylene propylene diene monomer (EPDM) rubber has been described that has two small circular through-thickness inserts consisting of EPDM modified and mixed with additives to improve its damping properties in "TOV Abschlussbericht TRCH-17-3011 - Larm und LCC- optimierte Schienenzwischenlagen", Version 1.1, dated 14.12.2018 (https ://www.aramis. admin. ch/Texte/?ProjectID=40275). The results indicate that these pads do not to reduce noise with respect to a standard rail pad with the same static stiffness of 60 kN/mm. No improvement of superstructure protection has been reported.
Accordingly, despite the large amount of work done to optimize rail pad performances, a rail pad capable of significantly reducing airborne noise while optimally fulfilling its primary purposes of track protection is still lacking and is highly desirable.
DESCRIPTION OF THE INVENTION In view of the above-described drawbacks and limitations affecting the prior art solutions in the field of rail pads, an object underlying the present invention is to provide an improved rail pad that enhances an elastic decoupling between the rail and sleeper under static and low frequency compressive loading, hence shielding the track superstructure from damage due to transient load peaks during train pass-by and limiting low frequency ground-borne vibrations, while not increasing airborne noise over existing technical solutions.
Another object underlying the present invention is to reduce rail vibration and radiation of airborne noise over a large part of the audible frequency range between 20 and 20Ό00 Hz while not increasing track superstructure damage due to transient load peaks during train pass-by and limiting low frequency ground-borne vibrations.
A further object of the present invention is to provide a manufacturing method for the multi-material rail pad according to the present disclosure.
These objects are at least partially solved by a rail pad according to claim 1 and a method for manufacturing a rail pad according to claim 27.
In particular, the above-mentioned objects are at least partially solved by a rail pad comprising: a) a pad matrix comprising or consisting of a first material and b) at least one damping element at least partially encapsulated or embedded in the pad matrix, said damping element comprising or consisting of a second material, wherein the second material of the at least one damping element has a damping factor tan delta > 0.5 at a frequency of 1000 Hz at room temperature.
In a method for manufacturing a rail pad, the above-mentioned objects are at least partially solved in that the method comprises the steps of: a) preparing in a preform at least one damping element comprising or consisting of a material having a damping factor tan delta > 0.5 at a frequency of 1000 Hz at room temperature; b) introducing in a mold the before-prepared at least one damping element; and c) performing a multi-step molding process to at least partially encapsulate or embed the at least one damping element with a pad matrix. These solutions according to the present invention have the advantage over rail pads known from the prior art that a new kind of rail pads is provided by including into an elastic matrix one or more discrete elements with a chemical structure and mechanical properties distinct from those of said matrix, and with high damping properties over a large part of the audible frequency range between 20 and 20Ό00 Hz, thereby ensuring that the vibrations of the rail and other superstructure components that give rise to airborne noise are efficiently damped by transforming at least part of the vibrational energy into other forms of energy within the pad, as well as by mechanical coupling between the rails and the sleepers. By combining multiple materials with different stiffnesses and damping properties and appropriate geometries, it is therefore possible according to the present invention to tailor the strain distribution within the pad and obtain optimum frequency-dependent stiffness-damping combinations under specific loading modes, a possibility not achievable using singlematerial rail pad designs as known in the art. Importantly, rail pads according to the present invention fulfill all the standard technical requirements for track performance and stability over time and in the temperature range corresponding to service conditions.
The invention is based, at least in part, on the observation that in conventional single-material rail pads known from the prior art, noise mitigation is predominantly due to coupling of the rails to the sleepers, ballast and track substructure, which is determined in turn by the rail pad dynamic stiffness. Materials such as EVA, HDPE, PU, EPDM rubber, with suitable elastic performance and durability, and in particular resilience, do not show significant intrinsic materials damping when deformed in the audible frequency range.
Further embodiments of the present invention are defined by the appended claims and are described in the following. The solutions according to the present invention can be combined as desired and further improved by the further embodiments that are advantageous on their own in each case. Unless specified to the contrary, the embodiments can be readily combined with each other. A skilled person will easily understand that all product features of rail pads according to the present invention may as well be implemented as and/or constitute steps of a method according to the present invention for manufacturing such rail pads and vice versa.
According to an embodiment of the present invention, the at least one damping element takes up or constitutes between 10 and 90% of a total volume of the rail pad.
According to an embodiment of the present invention, the rail pad comprises a single damping element.
According to an embodiment of the present invention, the rail pad comprises a plurality of damping elements.
According to an embodiment of the present invention, said at least one damping element has a polygonal or circular cross-section in at least one plane, forming cuboids, spheres, ellipsoids, cylinders, or prisms.
According to an embodiment of the present invention, said at least one damping element comprises a plurality of monodispersed or polydispersed particle-like units.
According to an embodiment of the present invention, said plurality of monodispersed or polydispersed particle-like units have an average dimension comprised between 50 nanometers and 1 millimeter.
According to an embodiment of the present invention, the at least one damping element is configured as a sheet or film.
According to an embodiment of the present invention, said sheet or film comprises at least one corrugated surface.
According to an embodiment of the present invention, said at least one damping element comprises or consists of at least one material selected from a non-limiting list comprising polyisobutylene (PIB), crosslinked polyisobutylene (butyl rubber, IIB), polyurethane elastomers (PU), polymer-modified bitumen, polar polymers, such as nitrile, hydrogenated or carboxylated nitrile rubber (NBR, HNBR, XNBR), chlorinated polyolefins (for example, polychloroprene (CR), chlorinated polyethylene or polypropylene, or chlorosulfonated polyethylene), acrylate rubbers (ACM) or epoxidized rubbers (ER), particularly where these have been modified with polar fillers and/or plasticizers or antiplasticizers, conventional vulcanized rubbers such as natural rubber (NR) or synthetic polyisoprenes (PI), polybutadiene (PBD), styrene-butadiene rubber (SBR), styrene-butadiene-styrene block copolymers (SBS), ethylene-propylene diene monomer rubber (EPDM), particularly where these contain high proportions of carbon black or silica fillers and/or plasticizers or antiplasticizers. These materials may be further processed into composites that may contain additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, calcium carbonate, talc, kaolin, wollastonite, rubber particles, polymer foam beads, cellulose or cellulose-based materials, cork particles or metallic inclusions.
According to an embodiment of the present invention, said pad matrix comprises or consists of at least one material selected from a nonlimiting list comprising crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene-propylene-diene monomer (EPDM) rubber or natural rubber (NR), synthetic cis 1,4-polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene- butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as isotactic polypropylene-vulcanized ethylene-propylene-diene-monomer (EPDM) blends, copolyester elastomers (COPE), or polyamide elastomers (PAE). These materials may be further processed into composites that may contain additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, calcium carbonate, talc, kaolin, wollastonite, rubber particles, polymer foam beads, cellulose or cellulose-based materials, cork particles or metallic inclusions.
According to an embodiment of the present invention, said pad matrix and/or said at least one damping element comprises at least one of pores, cavities and voids.
According to an embodiment of the present invention, said pores, cavities and/or voids are sized and distributed so that the pad matrix and/or the at least one damping element is configured as a close- celled or open-celled foam.
According to an embodiment of the present invention, said rail pad further comprises one or more stiffness modifying element(s) comprised within or onto the pad matrix, and separated from the at least one damping element.
According to an embodiment of the present invention, the one or more stiffness modifying element(s) comprises or consists of a material that increases the stiffness of at least a portion of the pad matrix, relative to the stiffness of the pad matrix itself, by having elastic moduli at least one of which is higher than the corresponding matrix modulus. The elastic moduli may comprise at least one of a bulk, shear or tensile modulus, or any one of the independent moduli shown by an isotropic material.
According to an embodiment of the present invention, the one or more stiffness modifying element(s) comprises or consists of a material that decreases the stiffness of at least a portion of the pad matrix, relative to the stiffness of the pad matrix itself, by having elastic moduli at least one of which is lower than the corresponding matrix modulus.
According to an embodiment of the present invention, the one or more stiffness modifier(s) has or have a polygonal or circular cross-section in at least one plane, forming cuboids, spheres, ellipsoids, cylinders, or prisms.
In a further embodiment of method according to the present invention, at least one stiffening modifier is being introduced into the mold before performing the multi-step molding process.
Another alternative or additional method is coextrusion using two or more conventional single or twin screw extruders or one or more conic extruders, for example, sending separate thermoplastic materials feeds, including porogens or reactive components if desired, into a single die to produce, in a continuous process, a continuous solid or foamed object with a uniform cross-section perpendicular to the extrusion direction that may be rectangular, circular, tubular or any other two-dimensional shape, and in which the cross-sections of the individual components may be of any two-dimensional shape. The extruded object may then be cut into the desired length and width of the final part. Such a process would be suitable for the production of a planar sandwich geometry consisting of parallel layers of two or more different materials, or a planar sandwich geometry containing grooves or bosses, provided these have a uniform cross-section in the extrusion direction, or a sandwich geometry in which the whole rail pad and/or the individual components are corrugated, or take some other form, provided it or they have a uniform cross-section in the extrusion direction. Other types of external features such as grooves or bosses may be added later by machining or press-molding, press-forming or thermoforming. The external geometry of the whole pad and its elements may be further modified conformally by press-forming or thermoforming using suitable die shapes so as to introduce, for example, one- or two-dimensional corrugations or other shapes as desired.
Another alternative or additional method is successive casting. Simple sandwich geometries comprising solid or foamed elements with a uniform cross-section may be produced by successive continuous casting of different reactive pre-cursor materials onto a single- or double-belt apparatus or conveyer. These may then cur into the desired length and width of the final part and subjected to fost-forming operations in the same way as described for the co-extruded objects above.
Another alternative or additional method is a mechanical or adhesive assembly process, where preformed solid elements made of different materials, or multiple materials produced using suitable techniques may be assembled by a mechanical interference or snap fit, or using fasteners, or secured using a suitable adhesive. The preformed elements may be molded, extruded, cast, thermoformed or made using any processing technique compatible with the desired form and material. This method is suitable for any geometry in which the preformed elements may be assembled to form the final part or a preform for the final part without modifying their topology, or else in which a suitable cavity has been introduced by a machining operation. It is therefore not suitable, for example, for geometries in which one or more elements are fully encapsulated by a matrix or another element.
For any of the methods listed above, additional external features such as studs or ribs may either be molded-in or introduced subsequently by machining to the composite rail pad.
The whole composite rail pad typically comprises external dimensions in the absence of loading as follows: external width w is in a range of about 100 to 210 mm, particularly preferably in a range of about 120 to 200 mm, for example about 194 mm. The external length I of the said rail pad, which extends along the longitudinal direction L of the later track direction, is about 100 to 210 mm, more preferably about 160 to 200 mm, for example about 190 mm. The thickness or height h of the said rail pad is about 5 to 14 mm. The stiffness of the resulting composite rail pad is adjusted according to EN 13481-2-C or EN 13146-9 in such a way that the static vertical stiffness in compression (i.e., along the thickness or height h of the rail pad) varies in the range from 0 to >2000 kN/mm, but preferably in the range 50 to 200 kN/mm. The ratio of the dynamic stiffness to the static stiffness, i.e., the stiffening of the pad at 10 Hz (tested according to EN 13481-2-C or EN 13146-9), may be varied most preferably by the properties and/or special geometries of the at least one core damping elements, or by the use of special geometries of the pad matrix such as external grooves or studs.
According to a further embodiment of the present invention, said sheet may also include external studs or ribs or other types of profile on one or both major faces (i.e., those faces in direct physical contact with either the pad matrix, the sleepers, or the metallic rails).
According to a further embodiment of the present invention, said pad matrix and/or said at least one damping element may also include internal gaps or holes or grooves or other types of profile, either fully encapsulated by the respective material of the pad matrix and/or said at least one damping element or in direct physical contact with either the pad matrix, the sleepers, or the metallic rails. Said gaps or holes or grooves or other types of profile in the said pad matrix and/or said at least one damping element have the advantage of enabling modification of the dynamic stiffness of said pad matrix and/or said at least one damping element without modifying the intrinsic damping properties of said at least one damping element. Gaps contained entirely within the damping elements such as surface grooves in a planar damping element with depths less than the thickness of the damping element are advantageous because they allow the damping element to form a continuous interface with matrix, avoiding local lateral slip at the matrix-damping element interface.
According to a further embodiment of the present invention, said gaps or holes or grooves or other types of profile have the shape of cylinders with a spherical or ellipsoidal cross-section, or prisms with a polygonal cross-section, or grooves with a semispherical or semiellipsoidal or rectangular or triangular cross-section.
According to a further embodiment of the present invention, said grooves have rectilinear trajectories. Gaps in the form of grooves with rectilinear trajectories, e.g., parallel to the rail, are advantageous because they release lateral constraints on the deformation of the rail pad, reducing its overall stiffness and increasing the deformation in the damping elements for a given shape and size of the damping elements and a given vertical load.
According to a further embodiment of the present invention, said grooves have regular or irregular zigzag or curvilinear trajectories. Gaps in the form of grooves with zigzag or curvilinear trajectories are advantageous in that they allow more uniform release of lateral constraints on the deformation of the rail pad in damping elements of different widths and/or with respect to deformations parallel and perpendicular to the rail direction.
According to a further embodiment of the present invention, said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element are either filled with air or with a material different from the one used for the damping element, whose bulk modulus is lower than the bulk modulus of the damping element and/or the pad matrix. Filling said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element with a low bulk modulus material is advantageous because it prevents contamination of the interior of the gaps by dirt, abrasion products or other forms of extraneous matter, which would change their mechanical performance over time, without compromising the ability of the gaps to reduce lateral constraints on the deformation of the rail pad. According to a further embodiment of the present invention, said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element are filled with a material whose bulk modulus is a least one order of magnitude lower than that of the respective material used for the said pad matrix and/or said at least one damping element.
According to a further embodiment of the present invention, said gaps or holes or grooves or other types of profile of said pad matrix and/or said at least one damping element are filled with an elastomeric close- celled or open-celled foam.
In an additional or alternative further embodiment, the at least one damping element is configured as a sheet or film that may also include external studs or ribs or other types of profile on one or both major faces (i.e. those faces in direct physical contact with either the pad matrix, the sleepers, or the metallic rails).
According to a further embodiment of the present invention, the pad matrix may also include internal gaps or holes or grooves or other types of profile, either fully encapsulated by the pad matrix or in direct physical contact with either the pad matrix, the sleepers, or the metallic rails.
These further embodiments particularly help to reduce both rail vibration and radiation of airborne noise over a large part of the audible frequency range between 20 and 20Ό00 Hz while, at the same time, enhancing the elastic decoupling between the rail and sleeper under static and low frequency compressive loading, hence providing an improved shielding of the track superstructure from damage due to transient load peaks during train pass-by and limiting low frequency ground-borne vibrations.
Embodiments of the present invention described above and other objects, features and advantages of the herein presented subject- matter will become more apparent from a study of the following description with reference to the attached figures showing some preferred aspects of said subject-matter.
BRIEF DESCRIPTION OF THE DRAWINGS Further understanding of various aspects of the invention can be obtained by reference to the following detailed description in conjunction with the associated drawings, which are described briefly below. In the figures:
Fig. 1 shows schematic views of several embodiments of rail pads according to the present invention;
Fig. 2 shows respective schematic cross-sectional views of the rail pads shown in Fig. 1 as well as additional embodiments of rail pads according to the present invention;
Fig. 3a shows a Pareto performance plot for several embodiments of rail pads according to the present invention;
Fig. 3b shows a detail of Figure 3a with data for individual embodiments of rail pads according to the present invention;
Fig. 4 shows schematic perspective views of several embodiments of rail pad geometries according to the present invention corresponding to Figure 3;
Fig. 5a shows a schematic top view of three further embodiments of rail pads according to the present invention;
Fig. 5b shows a schematic cross-sectional view of the rail pads illustrated in Fig. 5a along the cross-sectional line A-A depicted therein;
Fig. 6a shows a schematic top view of a further embodiment of a rail pad according to the present invention;
Fig. 6b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 6a along the cross-sectional line A-A depicted therein; Fig. 7a shows a schematic top view of a further embodiment of a rail pad according to the present invention;
Fig. 7b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 7a along the cross-sectional line A-A depicted therein;
Fig. 8a shows a schematic top view of a further embodiment of a rail pad according to the present invention;
Fig. 8b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 8a along the cross-sectional line A-A depicted therein;
Fig. 9a shows a schematic top view of a further embodiment of a rail pad according to the present invention;
Fig. 9b shows a schematic cross-sectional view of the rail pad illustrated in Fig. 9a along the cross-sectional line A-A depicted therein;
Fig. 10a shows a Pareto performance plot for several further embodiments of rail pads according to the present invention; and
Fig. 10b shows a detail of Figure 10a with data for individual embodiments of rail pads according to the present invention.
TERMS AND DEFINITIONS
The subject-matter described in the following will be clarified by means of a description of those aspects which are depicted in the drawings. It is however to be understood that the scope of protection of the invention is not limited to those aspects described in the following and depicted in the drawings; to the contrary, the scope of protection of the invention is defined by the claims. Moreover, it is to be understood that the specific conditions or parameters described and/or shown in the following are not limiting of the scope of protection of the invention, and that the terminology used herein is for the purpose of describing particular aspects by way of example only and is not intended to be limiting.
Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, unless otherwise required by the context, singular terms shall include pluralities and plural terms shall include the singular. The methods and techniques of the present disclosure are generally performed according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification unless otherwise indicated. Further, for the sake of clarity, the use of the term "about" is herein intended to encompass a variation of +/- 10% of a given value.
Non-limiting aspects of the subject-matter of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labelled in every figure, nor is every component of each aspect of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.
The following description will be better understood by means of the following definitions.
As used in the following and in the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Also, the use of "or" means "and/or" unless stated otherwise. Similarly, "comprise", "comprises", "comprising", "include", "includes" and "including" are interchangeable and not intended to be limiting. It is to be further understood that where for the description of various embodiments use is made of the term "comprising", those skilled in the art will understand that in some specific instances, an embodiment can be alternatively described using language "consisting essentially of" or "consisting of."
The term "elastic" refers to a property of a material that can deform reversibly in one or more directions upon mechanical solicitations including expansion, contraction, bending, torsion, load, twist, linear or area strain and the like under typical operating loads, under both static and dynamic conditions, and shows no or small viscoelastic losses. According to some embodiments of the invention, typical elastic surrounding materials for the rail pad matrix have static moduli and dynamic storage moduli not exceeding 0.1 GPa when measured under uniaxial conditions at room temperature (20-30 C), and dynamic storage moduli not exceeding 0.5 GPa but preferably greater than 1 MPa and tan delta not exceeding 0.2 when measured under uniaxial conditions at room temperature (20-30 °C) and frequencies of up to 10Ό00 Hz. Suitable materials may include, but are not limited to, semicrystalline or elastomeric materials based on ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU) or polyurethane urea (PUE), crosslinked ethylene-propylene-diene monomer (EPDM) rubber, crosslinked natural (NR) or synthetic cis 1,4- polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene-butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as isotactic polypropylene-vulcanized ethylene-propylene-diene-monomer (EPDM) blends, copolyester elastomers (COPE), or polyamide elastomers (PAE).
The term "damping" refers to the restraint of vibratory motion, which may in turn cause noise, through energy dissipation. A "damping material" is a material with an intrinsic capacity to restrain vibratory motion through energy dissipation, usually in the form of heat. To characterize this capacity, we use the damping factor, tan delta, of the material. In a viscoelastic material, "tan delta" is the ratio of the loss modulus, which determines the rate of energy dissipation during mechanical deformation, to the storage modulus, which determines the amount of mechanical energy stored in the material for a given applied force or deformation. Tan delta may hence be determined from the phase and amplitude of the stress when a material is subjected to a cyclic deformation, for instance by using a disc rheometer under conditions of atmospheric pressure and at the desired temperature and frequency typically chosen to be in the range -150 to 300 °C and 0.01 to 100 Hz, respectively, as known in the art. Tan delta may be determined outside this frequency range at a given temperature from measurements at other temperatures making use of the time- temperature superposition principle, as again known in the art. It is also given by the ratio of the mechanical energy dissipated per radian during a loading cycle to the peak potential energy in the cycle, and is hence often called the "loss factor". Such alternative but strictly equivalent engineering definitions of tan delta in mechanical systems are the basis of standard test methods for tan delta (Vibration damping, A.D: Nashif, D.I.G. Jones, J.P. Henderson, Wiley, New York, 1985) exemplified by ASTM E756-04 (Standard test method for measuring vibration-damping properties of materials. American Society for Testing and Materials; 2004).
As used herein, "maximum dimension" refers to those parameters or measurements required to define the shape and/or size, such as height, width, and length, of an object. As used herein, the maximum dimension of a two-dimensional object, such as a rectangle, a polygon, or a circle, is the longest straight-line distance between any two points on the object. Therefore, the maximum dimension of a circle is its diameter; a rectangle its diagonal, and a polygon its longest diagonal. The maximum dimension of a three-dimensional object is the longest straight-line distance between any two points on the object.
The term "composite" refers to a material made up of different components that are chemically and/or morphologically distinct, and show dissimilar chemical and/or physical properties in the finished structure, distinguishing composites from homogeneous mixtures or solid solutions. Composites may therefore show property profiles that cannot be achieved with the individual components. The terms "composite" and "multi-material" are used interchangeably in the frame of the present disclosure.
The term "foam", as used herein, refers to a substance that is formed by encompassing a plurality of polydisperse or monodisperse gas bubbles, referred to herein as "cells", within a mass of a liquid or a solid, constituting the films of walls separating the cells. In the context of solid foams, according to some embodiments of the invention, the regions occupied by a tangible condensed mass are regarded as the "solid" fraction of the foam, while all other regions not occupied by this fraction are regarded as the "gas" fraction of the foam. According to some embodiments of the present invention, the foam is a combination of a polymeric porous solid matrix and gas-filled cells, typically filled with ambient air. The phrase "porous solid matrix", as used herein, refers to the non-gaseous part of the foam, which contributes substantially to the mass of the foam but substantially less to its volume. Porous materials in general are classified either as "open" or "closed" foams. In the terminology of foam science, closed foams have "cells" (pores, voids) where the faces shared with neighboring "cells" are solid membranes; these closed foams entrap the pore fluid, which cannot easily escape through the solid membranes delimiting the "cells". Classical open foams have no membranes between neighboring cells, but only struts along the edges where three or more cells meet. Such open foams naturally have a fully interconnected pore space, and a fibrous network of solid material. According to some embodiments of the present invention, the polymeric foam composition presented herein is characterized by a density (p) that ranges from 0.01 to 2 grams per centimeter cubed, such as from 0.05 to 0.9 grams per centimeter cubed.
WAYS OF CARRYING OUT THE INVENTION
Fig. 1 shows a schematic illustration of several embodiments of a multimaterials rail pad 10, lOa-f according to the present invention, namely: la) a rail pad 10a with matrix la comprising a single centred cuboid damping element 2a, lb) a rail pad 10b with matrix lb comprising four cuboid damping elements 2b, lc) a rail pad 10c with matrix lc comprising a single centred cylindrical damping element 2c,
Ld) a rail pad lOd with matrix Id comprising four cylindrical damping elements 2d, le) a rail pad lOe with matrix le comprising a single centred cuboid damping element 2e and two stiffness modifying elements 3e, and
Lf) a rail pad lOf with matrix If comprising a single centred cuboid damping element 2f and two stiffness modifying elements 3f, where the stiffness modifying elements 3f comprise particulate inclusions. The multi-material rail pads 10, lOa-f comprises the pad matrix 1, la-f comprising or consisting of a first material and the at least one damping element 2, 2a-f at least partially encapsulated or embedded in the pad matrix 1, la-f, said damping element(s) 2, 2a-f comprising or consisting of a second material, wherein the second material of the at least one damping element 2, 2a-f has a damping factor tan delta > 0.5 at a frequency of 1000 Hz.
Fig. 2 shows possible schematic cross-sectional views of the embodiments of rail pad lOa-f according to the present invention shown in Fig. la and alternative versions and/or further embodiments lOg, lOh, lOi thereof in parallel to the rail direction at mid-point of the rail pad (matrix 1, damping element(s) 2, stiffness modifying elements 3). Here it becomes apparent that the damping elements 2, 2a-i may have the following dimensions, forms and/or shapes: a. single centred cuboid damping element of thickness less than overall rail pad thickness (cf. Figure 3b points j-n,p)), b. multiple cuboid damping element of thickness less than overall rail pad thickness (cf. Figure 3b point o)), c. single centred cuboid damping element of thickness equal to overall rail pad thickness (cf. Figure 3b point q)), d. multiple cuboid damping elements of thickness equal to overall rail pad thickness (cf. Figure 3b points r,s)), e. single centred corrugated cuboid damping element of thickness less than overall rail pad thickness (cf. Figure 3b points t-v)), f. single centred cuboid damping element of thickness less than overall rail pad thickness + surface grooves to modify stiffness, g. single centred cuboid damping element of thickness less than overall rail pad thickness + surface studs to modify stiffness, h. single centred cuboid damping element of thickness less than overall rail pad thickness flush with bottom surface + surface grooves to modify stiffness, and i. single centred cuboid damping element of thickness less than overall rail pad thickness with stiffness modifying elements. Fig. 3a shows a schematic Pareto performance plot for multimaterials rail pads based on an ethylene vinyl acetate (EVA) matrix containing modified polyisobutylene (PIB) damping elements: the tangent delta and stiffness values are for the compression of the whole of the rail pad between two rigid plates in each case:
(a) Reference EVA hard rail pad (static stiffness = 1359 kN/mm, tan delta at l'OOO Hz = 0.15),
(b) reference PUR soft rail pad (static stiffness = 30, tan delta at l'OOO Hz = 0.09), (c) reference PIB high damping rail pad (static stiffness = 205 kN/mm, tan delta at l'OOO Hz = 0.73) ,
(d)multiple planar damping elements or a single centred planar damping element of thickness less than overall rail pad thickness (circles), (e)multiple planar damping elements or a single centred planar damping element of thickness equal to overall rail pad thickness (triangles), and
(f) single centred corrugated damping element of thickness less than overall rail pad thickness (lozenges) Figure 3b shows a detail of Figure 3a with the following data for individual rail pads 10, which are numbered as follows, with reference to the rail pad geometries shown in Fig. 4: lOj) Static stiffness = 889 kN/mm, tan delta at l'OOO Hz = 0.35, PIB content = 15 vol%, insert thickness = 1.04 mm; 10k) static stiffness = 482 kN/mm, tan delta at l'OOO Hz = 0.56, PIB content = 45 vol%, insert thickness = 3.14 mm;
101) static stiffness = 372 kN/mm, tan delta at l'OOO Hz = 0.62, PIB content = 60 vol%, insert thickness = 4.20 mm; 10m) static stiffness = 658 kN/mm, tan delta at l'OOO Hz = 0.28, PIB content = 28.6 vol%, insert thickness = 2 mm;
10h) static stiffness = 294 kN/mm, tan delta at l'OOO Hz = 0.67, PIB content = 75 vol%, insert thickness = 5.24 mm; lOo) static stiffness = 685 kN/mm, tan delta at l'OOO Hz = 0.38, PIB content = 33.3 vol%, insert thickness = 5.24 mm (4 inserts); lOp) static stiffness = 708 kN/mm, tan delta at l'OOO Hz = 0.34, PIB content = 33.3 vol%, insert thickness = 5 mm (cross-shaped); lOq) static stiffness = 481 kN/mm, tan delta at l'OOO Hz = 0.45, PIB content = 61.6 vol%; lOr) Static stiffness = 760 kN/mm, tan delta at l'OOO Hz = 0.25, PIB content = 55.6 vol% (4 inserts);
10s) static stiffness = 520 kN/mm, tan delta at l'OOO Hz = 0.34, PIB content = 66.6 vol% (2 inserts); lOt) static stiffness = 821 kN/mm, tan delta at l'OOO Hz = 0.37 , PIB content = 17.4 vol%, insert height = 4 mm, insert thickness = 1 mm; lOu) static stiffness = 853 kN/mm, tan delta at l'OOO Hz = 0.38 , PIB content = 15 vol%, insert height = 5 mm, insert thickness =
1.71 mm; and lOv) static stiffness = 634 kN/mm, tan delta at l'OOO Hz = 0.42 , PIB content = 33.3 vol%, insert height = 5 mm, insert thickness = 3.79 mm.
The multi-material rail pads can be grouped into three groups: (A) rail pads 10 according to the present invention with improved acoustic performance and improved or maintained superstructure protection performance, compared to a reference rail pad made from EVA; (B) rail pads according to the present invention with improved superstructure protection performance and improved or maintained acoustic performance, compared to a reference rail pad made from EVA; (C) multi-material rail pads 10 with inferior acoustic and/or superstructure protection performance (counter examples)
Fig. 4 shows the geometries of the rail pads lOj-v that correspond to the numbers in the Pareto diagram shown in Fig. 3b, partially including sheets or film 11.
In the disclosed multi-material rail pad lOa-v, one or more optional air gaps may be introduced according to further embodiments of the present invention.
Fig. 5a shows a schematic top view of a further embodiment of a rail pad 10, 10a according to the present invention. The rail pad 10a has a static stiffness of 477 kN/mm, tan delta at l'OOO Hz of 0.63, PIB content of 60 vol%, and further comprises four grooves 5 running along the top side essentially in parallel to each other as well as to a rail direction R of a rail (not shown). The grooves 5 have a groove width W5 of, e.g., 5 mm, and a groove depth ts of, e.g., 2 mm.
The two inner grooves 5 are arranged at a first distance di from each other of, e.g., 72 mm measured essentially in a direction perpendicular to the rail direction R. The two outer grooves 5 are arranged at an edge of the core damping element 2 adjacent to an outer rim of the pad matrix 1 of the rail pad 10a. The two outer rims of the rail pad 10a are arranged at a second distance of 140 mm from each other measured essentially in a direction perpendicular to the rail direction R.
A further embodiment of a rail pad 10, 10b according to the present invention has a static stiffness of 508 kN/mm, tan delta at 1Ό00 Hz of 0.44, and a PIB content of 45 vol%, again with a groove width of 5 mm as well as corresponding distances di and dn. A further embodiment of a rail pad 10, 10y according to the present invention has a static stiffness of 301 kN/mm, tan delta at 1Ό00 Hz of 0.59, and a PIB content = 60 vol%, again with a groove width of 5 mm as well as corresponding distances di and di. Fig. 5b shows a schematic cross-sectional view of the rail pads 10a, b,g illustrated in Fig. 5a along the cross-sectional line A-A depicted therein. Here it becomes apparent that the gooves 5 have a groove depth ts measured in the height direction of the rail pad 10a, b,g. For example, the rail pads 10a, b each comprise grooves 5 having a groove depths of 2 mm, while the rail pad 10g has a groove depth of 4 mm.
Figs. 6a and 6b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10d according to the present invention comprising four grooves 5. The rail padl06 has a static stiffness of 293 kN/mm, tan delta at l'OOO Hz of 0.66, and PIB content of 60 vol%. The grooves 5 have a groove width ws of 5 mm, and a groove depth of 2 mm. The two inner grooves 5 are arranged at a first distance d5i from each other of, e.g., 40 mm, and the outer edges of the two outer grooves 5 are arranged at a second distance d52 of, e.g., 109 mm from each other, both measured essentially in a direction perpendicular to the rail direction R.
Figs. 7a and 7b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10e according to the present invention comprising two grooves 5 crossing each other in the center of the rail pad 10e as they extend diagonally between corners of the rail pad 10e diametrally opposing each other. The rail pad 10e has a static stiffness of 362 kN/mm, tan delta at 1Ό00 Hz of 0.58, and a PIB content of 60 vol%, while the grooves have a groove width Ws of 5 mm, and a groove depth t2 of 2 mm.
Figs. 8a and 8b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10z according to the present invention comprising two grooves 5 extending along the top of the rail pad 10z along the rail direction R and describing a serpentine line or sine wave with a length of a quarter cycle TT/2 of 17.5 mm measured essentially in parallel to the rail direction R. The rail pad 10z has a static stiffness of 472 kN/mm, tan delta at l'OOO Hz of 0.72, and a PIB content = 60 vol%. The grooves 5 are formed mirror symmetrically to each other with respect of a center line of the rail pad 10z extending along the rail direction R. The grooves have a groove width ws of 5 mm, a groove depth of 2 mm, and are distanced from the outer rim of the rail pad lOz by a mean first distance dZi of 35mm while the second distance d2 bettween the outer rims of the rail pad 10z again amounts to 140 mm.
Figs. 9a and 9b show a schematic top view, and cross-sectional view, respectively, of a further embodiment of a rail pad 10, 10h according to the present invention. The rail pad 10h has a static stiffness of 322 kN/mm, tan delta at l'OOO Hz of 0.59, and a PIB content of 60 vol%, and further comprises four grooves 5 running along the top side essentially in parallel to each other as well as to the rail direction R which are each filled with stiffness modifying elements 3 as inserts formed of PU foam. The grooves 5 and therefore the stiffness modifying elements 3 have a insert width W3 of 5 mm, and an insert height f of = 4 mm.
The two inner stiffness modifying elements 3 are arranged at the first distance di from each other of, e.g., 72 mm measured essentially in a direction perpendicular to the rail direction R. The two outer stiffness modifying elements 3 are arranged at the edge of the core damping element 2 adjacent to the outer rim of the pad matrix 1 of the rail pad 10h. The two outer rims of the rail pad 10 h are arranged at the second distance of 140 mm from each other measured essentially in a direction perpendicular to the rail direction R.
Fig. 10a shows a schematic Pareto performance plot for multimaterials rail pads 10, 10a-h based on an ethylene vinyl acetate (EVA) matrix containing modified polyisobutylene (PIB) damping elements: the tangent delta and stiffness values are for the compression of the whole of the rail pad 10a-h between two rigid plates in each case. Fig. 10b shows a detail of Figure 10a including rail pads 10, lOa-v corresponding to those shown in Figs. 3a and 3b, and in addition rail pads 10, 10a-h. The multi-material rail pads lOa-v can again be grouped into three groups: (A) rail pads according to the present invention with improved acoustic performance and improved or maintained superstructure protection performance, compared to a reference rail pad made from EVA; (B) rail pads according to the present invention with improved superstructure protection performance and improved or maintained acoustic performance, compared to a reference rail pad made from EVA; (C) rail pads 10 with inferior acoustic and/or superstructure protection performance (counter examples).
Rail pads 10a-h can be grouped into a fourth group (D), which contains multimaterials rail pads according to the present invention containing air gaps or compressible foam inserts with improved acoustic performance and improved or maintained superstructure protection performance, compared to a reference rail pad made from EVA. In comparison with groups (A), (B), rail pads from group (D) in general show improved acoustic performance over rail pads from group (B) with comparable superstructure protection performance, because the release of lateral constraints in the damping elements 2a-h due to the stiffness modifying elements 3 and/or grooves 5 increases damping performance, and improved superstructure performance over rail pads from group (A) with comparable acoustic performance, because the release of lateral contraints due to the stiffness modifying elements 3 and/or grooves 5 reduces the overall stiffness of the railpad.
In other words, Group A contains examples of rail pads 10 according to the present invention with significantly improved acoustic performance and maintained or improved superstructure performance in comparison with the prior art. Rail pads 10j,k,o,p,u,t,v represent designs examples which typically are rich in damping material and do not comprise any grooves. Group B contains rail pads 10 as examples with significantly improved superstructure performance and maintained or improved acoustic performance in comparison with the priort art. Rail pads 2l,m,n represent design examples containing less damping material than rail pads 10j,k,o,p,u,t,v and neither comprise any grooves. With rail pads 10q,r,s, group C contains some reference examples of relatively low performance. Group D contains examples of rail pads 10a-h according to the present invention with significantly improved acoustic and superstructure performance in comparison to the prior art and having varying amounts of damping material (based on designs in groups A or B) and grooves.
Advantageously, the material of the at least one damping element 2, 2a-v, 2a-h may have a damping factor tan delta > 0.65 at a frequency of 1000 Hz. Advantageously, the material of the at least one damping element 2, 2a-v, 2a-h may have a damping factor tan delta > 0.8 at a frequency of 1000 Hz. Advantageously, the material of choice shows significant damping over a significant portion of the audible frequency range, namely a tan delta > 0.5 for audible frequencies > 200 Hz, and/or tan delta > 0.8 for audible frequencies > 1000 Hz. All of these values refer to the intrinsic tan delta of the second, damping material of the damping element 2a-v, 2a-h at room temperature.
The rail pad 10, lOa-v, 10a-h has an overall plate-like geometry suitable for insertion between a rail and a railway sleeper and have lengths I, widths w, and heights h, that are standardized. (Other geometries are possible as required by the railway superstructure.)
The multi-material rail pads 10, lOa-v, 10a-h are at least formed of a pad matrix la-v, la-h and at least one damping element 2a-v (see Figs. 1, 2, 4, and 5a to 9b). The damping element 2a-v, 2a-h is preferably formed and arranged such that it is fully encapsulated and its center of mass lies in the mid-plane of the rail pad or, alternatively such that its top surface lies flush with the top surface of the rail pad 10, lOa-v, 10a-h such that the damping element 2a-v is touching the rail. This latter arrangement may, for example, facilitate fabrication. Optionally, the multi-material rail pads 10 a-v may contain at least one additional stiffness-modifying element 3a-v.
The pad matrix la-v, la-h of the composite rail pad 10, lOa-v, 10a-h, is made of a resilient elastic material forming the body of the composite rail pad 10, lOa-v, 10a-h.
The main role of the pad matrix la-v, la-h is to mechanically decouple the rail from the sleeper. The compression modulus of the pad matrix la-v, la-h should be chosen to ensure that the global static compression and shear stiffness requirements of the composite rail pad 10, lOa-v, 10a-h are met, depending on the elastic properties of the damping elements, depending on whether a "hard" (nominal throughthickness compressional stiffnesses in the range 200 to as much as 1'300 kN/mm) or "soft" (nominal through-thickness compressional stiffnesses in the range 30 kN/mm to 150 kN/mm) rail pad 10, lOa-v, 10a-h is desired. In at least one embodiment, the requirements of the European norm 13146 are followed and implemented in the rail pad 10, lOa-v, 10a-h of the invention. The pad matrix 1 should also preferably meet certain requirements for environmental and weathering resistance and temperature stability according to the needs and circumstances (for instance, the country in which it is used), and show adequate resilience, fatigue resistance, abrasion resistance and creep resistance: for example, a rail pad 10, lOa-v, 10a-h according to the present invention should not show permanent deformation on the time-scale of train pass-by or as a result of the related clamping force.
The pad matrix 1 may be prepared from an elastic material or a combination of elastic materials. It may be made from a single thermoplastic or thermoset or elastomeric material, including but not limited to crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene-propylene-diene monomer (EPDM) rubber or natural rubber (NR), which are already known and validated as suitable materials for rail pad manufacturing, and also synthetic cis 1,4-polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene- butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as isotactic polypropylene-vulcanized ethylene-propylene-diene-monomer (EPDM) blends, copolyester elastomers (COPE), or polyamide elastomers (PAE).
These materials may be further processed, in certain embodiments, into composites that contain additional organic or inorganic materials in the form of nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, glass fibers, carbon fibers, or polyamide fibers, or cork particles in order to possibly optimize the final stiffness. These thermoplastic or thermoset or elastomeric materials and their composites may optionally contain microscopic or macroscopic voids, pores and/or gaps.
The pad matrix 1 may additionally or alternatively by prepared from two or more of the porous or non-porous single thermoplastic or thermoset or elastomeric materials or their composites. Advantageously, the pores or gaps may be designed and/or distributed across the pad matrix 1 to reduce the final stiffness, not only by substituting part of the matrix with air, but also by increasing the compressibility of the material, so that it can deform more easily when confined between a rail and a sleeper. As it will appear evident, therefore, in one embodiment the pad matrix 1 of the invention may comprise or consist of a closed-cell or open-cell foam, preferably a closed-cell foam with a pore density of not more than around 30%, e.g., a pore density comprised between 1 and 10%, between 1 and 20% or between 1 and 30%.
In the disclosed multi-material rail pad 10, lOa-v, 10a-h, one or more damping element(s) 2, 2a-v, 2a-h are introduced. The main role of these one or more damping element(s) 2, 2a-v, 2a-h is to improve noise reduction and vibration damping without degrading the function of the rail pad to decouple the rails and sleepers mechanically. In at least one embodiment, the rail pad 10, lOa-v, 10a-h according to the invention comprises a single damping element 2. In an alternative embodiment, the rail pad 10, lOa-v, 10a-h according to the invention comprises plurality of damping elements 2.
The one or more damping element(s) 2, 2a-v, 2a-h are prepared from a damping material. It has been found that the damping material for the one or more damping element(s) 2, 2a-v, 2a-h should have a damping factor tan delta > 0.5 at a frequency of 1000 Hz. Advantageously, the material of the at least one damping element 2, 2a-v, 2a-h may have a damping factor tan delta > 0.65 at a frequency of 1000 Hz. equal to or greater than 0.5 at a frequency of 1000 Hz, particularly at 21 °C, such as a tan delta > 0.65 or > 0.8. The used materials also shows tan delta ranging from about 0.6 to 1.2 in the audible frequency range between 100 and 10Ό00 Hz, at room temperature.
The one or more damping element(s) 2, 2a-v, 2a-h can be prepared from a damping material, which is a thermoplastic or thermoset or elastomeric material with a dynamic modulus in the range 1-0.2 GPa and preferably in the range 10 MPa-0.2 GPa at l'OOO Hz and room temperature, selected from a non-limiting list comprising polyisobutylene (PIB), crosslinked polyisobutylene (butyl rubber, IIB), polyurethane elastomers (PU), polymer-modified bitumen, polar polymers, such as nitrile, hydrogenated or carboxylated nitrile rubber (NBR, HNBR, XNBR), chlorinated polyolefins (for example, polychloroprene (CR), chlorinated polyethylene or polypropylene, or chlorosulphonated polyethylene), acrylate rubbers (ACM) or epoxidized rubbers (ER), particularly where these have been modified with polar fillers and/or plasticizers or antiplasticizers, conventional vulcanized rubbers such as natural rubber (NR) or synthetic polyisoprenes (PI), polybutadiene (PBD), styrene-butadiene rubber (SBR), styrene- butadiene-styrene block copolymers (SBS), ethylene-propylene diene monomer rubber (EPDM), particularly where these contain high proportions of carbon black or silica fillers and/or plasticizers or antiplasticizers. These materials may be further processed into composites that may contain additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, calcium carbonate, talc, kaolin, wollastonite, rubber particles, polymer foam beads, cellulose or cellulose-based materials, cork particles or metallic inclusions. These thermoplastic or thermoset or elastomeric materials and their composites may optionally contain microscopic or macroscopic pores or gaps, which may be introduced directly into at least one damping element 2,2a-v, 2a-h, for example, by molding or using a suitable porogen, or via pre-formed second phase inclusions such as polymer foam beads.
The at least one damping element 2, 2a-v, 2a-h may constitute between 10 and 90% of the total volume of the rail pad 10, lOa-v, 10a-h, such as for instance between 15 and 60% of the total volume of the rail pad 10, lOa-v, 10a-h, between 15 and 30% of the total volume of the rail pad 10, lOa-v, 10a-h, between 30 and 70% of the total volume of the rail pad 10, lOa-v, 10a-h or between 40 and 80% of the total volume of the rail pad 10, lOa-v, 10a-h.
The one or more damping element(s) 2, 2a-v, 2a-h may be incorporated into the rail pad 10, lOa-v, 10a-h in different ways. The one or more damping element(s) 2, 2a-v, 2a-h may be incorporated into the rail pad 10, lOa-v, 10a-h in the form of one or more macroscoic units with defined geometries that comprise or consist of the damping materials listed above. The one or more damping element(s) 2, 2a-v, 2a-h may adopt any geometrical form including, but not limited to forms with a constant or varying polygonal, circular or elliptical cross-section, such as spheres, ellipsoids, cylinders, or prisms with a polygonal, elliptical, or circular base. If two or more damping elements 2, 2a-v, 2a-h are introduced, they may have the same or different geometrical forms. The one or more damping element(s) 2, 2a-v, 2a-h may span the whole height, or the whole width, or the whole length of the rail pad 10, lOa-v, 10a-h, or it may be entirely encapsulated/embedded by the pad matrix 1 and/or by the optional stiffness-modifying element(s) 3 on the top and/or bottom and/or either side and/or the top and/or the bottom of the rail pad 10, lOa-v, 10a-h.
In an additional or alternative embodiment, the at least one damping element 2, 2a-v, 2a-h is configured as a sheet or film, that may comprise at least one corrugated surface.
Additionally, or alternatively, the one or more damping element(s) 2, 2a-v, 2a-h may comprise the damping materials listed above in the form of a dispersion of microscopic or macroscopic damping particles in the matrix material, also referred to herein as "particle-like units". The damping particles may be monodisperse (that is, they all have the same size and shape) or polydisperse (that is, they have a distribution of sizes and shapes). Said plurality of monodisperse or polydisperse particle-like units have preferably a maximum dimension or an average dimension comprised between 50 nanometers and 1 millimeter. They may have regular shapes, such as ellipsoids or spheres, or be irregularly shaped (their concentration per unit volume varies depending on the location within the pad matrix 1).
The one or more damping element(s) 2, 2a-v, 2a-h that comprise said plurality of monodisperse or polydisperse particle-like units of the damping materials may again have a macroscopic shape with defined geometries. It may adopt any geometrical form including, but not limited to forms with a constant or varying polygonal, circular or elliptical cross-section, such as spheres, ellipsoids, cylinders, or prisms with a polygonal, elliptical, or circular base. If two or more regions of higher concentration of damping particles are present, they may have the same or different geometrical forms. They may span the whole height, or the whole width, or the whole length of the rail pad 10, 10a- v, 10a-h, or they may be encapsulated/embedded by the pad matrix 1 and/or the optional reinforcing element 3 on the top and/or bottom and/or either side and/or the top and/or the bottom of the rail pad 10, lOa-v, 10a-h.
As for the pad matrix 1, in any embodiment, the damping materials and their composites may optionally contain microscopic or macroscopic void, pores and/or gaps. The damping element(s) 2, 2a-v, 2a-h may also comprise or consist of a foam, such as close-celled or open-celled foams with a pore density of not more than around 30%, e.g., a pore density comprised between 1 and 10%, between 1 and 20% or between 1 and 30%.
The geometry and placement of the one or more damping element(s) 2, 2a-v, 2a-h and the spatial distribution of the optional two or more damping elements 2, 2a-v, 2a-h are tailored in order to ensure long term mechanical stability, while favoring damping of deformation modes of the rails during train pass-by that are associated with noise generation, such as pin-pin vertical flexural modes in the audible frequency range.
The rail pad 10, lOa-v, 10a-h may have a core-shell morphology comprising a hard elastic matrix 1 fully encapsulating a centered cuboid damping element 2, wherein said damping element 2, 2a-v, 2a- h constitutes between 15 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h.
Alternatively, or additionally, the rail pad 10, lOa-v, 10a-h may have a core-shell morphology comprising a hard elastic matrix 1 fully encapsulating a centered cuboid damping element 2, wherein said damping element 2, 2a-v, 2a-h constitutes between 30 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h. Alternatively, or additionally, the rail pad 10, lOa-v, 10a-h may have a core-shell morphology with a hard elastic matrix 1 fully encapsulating a centered corrugated cuboid damping element 2, wherein said damping element 2, 2a-v, 2a-h constitutes between 15 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h.
The rail pad 10, lOa-v, 10a-h may have a core-shell morphology with a hard elastic matrix 1 fully encapsulating a corrugated centered cuboid damping element 2, wherein said damping element 2, 2a-v, 2a- h constitutes between 30 and 60 % of total volume of the rail pad 10, lOa-v, 10a-h.
The obtained rail pad 10, lOa-v, 10a-h shows optimized acoustic performances (i.e., reduction of airborne noise at audible frequencies between 200 to about 2000 Hz), and better track protection performances than a reference material (EVA) typically used in rail pads. The obtained rail pads 10, lOa-v, 10a-h have a static stiffness in the range of 500-1000 kN/mm, tan delta (of the pad) between 0.3 and 0.6 at 1000 Hz, and a damping material (e.g., PIB) content between 15 and 50%. In a sub-group, the obtained pads 10, lOa-v, 10a-h have a static stiffness in the range of 700-1000 (e.g., between 800 and 900) kN/mm, tan delta (of the pad) between 0.3 and 0.5 (e.g., between 0.3 and 0.4), and a damping material (e.g., PIB) content between 15 and 20%. Within certain limits and constraints, the exact geometry of the damping element 2, 2a-v, 2a-h does not have a major impact on the performances, whereas the presence, placement, and geometry of optional grooves 5 or stiffness modifying elements 3 does, and full encapsulation (height of the damping element < pad thickness) shows good results.
The obtained rail pad 10, lOa-v, 10a-h shows optimized track protection performances, and better or similar acoustic performance than a reference material (EVA) typically used in rail pads known from the prior art. The obtained rail pads 10, lOa-v, 10a-h have a static stiffness in the range of 300-800 kN/mm, tan delta (of the pad) between 0.2 and 0.7 at 1000 Hz, and a damping material (e.g., PIB) content between 30 and 70%. In a sub-group, the obtained pads 10, lOa-v, 10a-h have a static stiffness between 250 and 500 (preferably between 300 and 400) kN/mm, tan delta (of the rail pad 10) between 0.4 and 0.8 (preferably between 0.6 and 0.8), and a damping material (e.g., PIB) content between 40 and 80%. Within certain limits and constraints, the exact geometry of the damping element 2, 2a-v, 2a-h does not have a major impact on the performances, whereas the presence, placement, and geometry of optional grooves 5 or stiffness modifying elements 5 does.
In the disclosed multi-material rail pad 10, lOa-v, 10a-h, one or more optional stiffness-modifying element(s) 3 may be introduced. The main role of the one or more optional stiffness-modifying element(s) 3 is to tailor the local mechanical stiffness of at least portion of the pad matrix 1. It is placed in specific locations within or onto the pad matrix 1 as required to increase or decrease its stiffness locally with respect to specific modes of mechanical solicitation. For instance, the one or more stiffness-modifying element 3 may separate at least two damping elements 2. The at least one optional stiffness-modifying element 3 should also meet standard requirements for environmental and weathering resistance and temperature stability and show adequate resilience, fatigue resistance, abrasion resistance and creep resistance over the whole range of service conditions. The at least one stiffnessmodifying element 3 is preferably separated from the at least one damping element 2.
The one or more optional stiffness-modifying element(s) 3 can be used as rigidifying elements. The compression modulus and shear stiffness of the one or more optional stiffness-modifying element(s) 3 are chosen to be equal to, or higher than, those of the pad matrix 1. Accordingly, the stiffness-modifying element(s) 3 comprises or consists of a material that increases the stiffness of at least a portion of the pad matrix 1, relative to the stiffness of the pad matrix 1 itself, thereby rigidifying at least a portion of the rail pad.
The one or more optional stiffness-modifying element(s) 3 may be prepared from an elastic material or a combination of materials. It may be made from a single thermoplastic or thermoset or elastomeric material, including but not limited to crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene-propylene-diene monomer (EPDM) rubber, or crosslinked natural rubber (NR) or any other organic or inorganic material, such as a metal, provided that the said material have one more elastic moduli different from those of the matrix material. These materials may be processed into composites that may contain additional organic or inorganic materials as nanoscopic, microscopic, or macroscopic fillers, including but not limited to carbon black, silica, glass fibers, carbon fibers, or nylon fibers.
Alternatively or additionally, the one or more optional stiffnessmodifying element(s) 3 are used as softening elements. Their compression modulus and shear stiffness of the one or more optional stiffness-modifying element(s) 3 are chosen to be equal to, or lower than, those of the pad matrix 1. Accordingly, the stiffness-modifying element(s) 3 comprises or consists of a material that decreases the stiffness of at least a portion of the pad matrix 1, relative to the stiffness of the pad matrix 1 itself, thereby softening at least a portion of the rail pad 10, lOa-v, 10a-h.
The one or more optional stiffness-modifying element(s) 3 to be used as softening elements may be prepared from a single thermoplastic or thermoset or elastomeric material, including but not limited to crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene- propylene-diene monomer (EPDM) rubber, or crosslinked natural rubber (NR), a compressible elastic material such as a material containing macroscopic cavities, including naturally occurring porous materials such as cork, or an elastomeric foam, including but not limited to a polyurethane (PU) foam, crosslinked ethylene-propylene- diene monomer (EPDM) rubber foam or crosslinked natural rubber (NR) foam, provided that the said material have one or more elastic moduli (i.e. bulk modulus, shear modulus and tensile modulus, or a multiplicity of moduli in the case of an isotropic material) lower than those of the matrix material.
The rail pad 10, lOa-v, 10a-h may comprise one or more optional stiffness-modifying element(s) 3 that combine the materials listed for the rigidifying and the softening elements. The rail pad 10, lOa-v, 10a- h may comprise one or more optional stiffness-modifying element(s) 3 that are used as rigidifying elements as well as one or more optional stiffness-modifying element(s) 3 that are used as softening elements.
The rail pad 10, lOa-v, 10a-h comprising the pad matrix 1 and the at least one damping element 2, 2a-v, 2a-h and the at least one optional reinforcing element 3 is preferably prepared by methods known in the art such as (plastic) extrusion, compression molding, resin transfer molding or injection molding method or reactive extrusion, reactive compression molding, reactive resin transfer molding or reactive injection molding, if required in the presence of a chemical or physical porogen but may also be prepared by casting, or certain individual components may be pre-formed by casting, extrusion, compression molding, resin transfer molding, injection molding, calendering, thermoforming or additive manufacture, or reactive extrusion, reactive compression molding, reactive resin transfer molding, reactive injection molding or reactive casting, if required in the presence of a chemical or physical porogen, or any other suitable technique for solid or porous thermoplastic or elastomeric parts, and subsequently combined with the other components in a multi-step molding procedure such as compression molding, or over-injection molding or with a film stacking procedure combined if required with intermediate cutting, shaping or machining steps, and/or gluing, welding or mechanical assembly.
Most preferred is the preforming of damping elements 2, 2a-v, 2a-h from a suitable damping material according to the invention by extrusion, injection molding, compression molding or any other suitable process, incorporating crosslinking and/or a porogen if required, the subsequent introduction of the damping elements 2, 2a- v, 2a-h into a mold cavity and subsequent overmolding with the material constituting pad matrix 1. Optionally, the at least one reinforcing element 3 is preformed by extrusion, injection molding, compression molding or any other suitable process, incorporating crosslinking and/or a porogen if required, subsequently introduced into a mold cavity together with the damping elements 2, and subsequently overmolded with the material constituting pad matrix 1. Additional external features such as studs or ribs may either be molded-in or introduced subsequently by machining to the composite rail pad 10, lOa-v, 10a-h.
The whole composite rail pad 10, lOa-v, 10a-h typically comprises external dimensions in the absence of loading as follows: external width w is in a range of about 100 to 210 mm, particularly preferably in a range of about 120 to 200 mm, for example about 194 mm. The external length I of the said rail pad 10, lOa-v, 10a-h, which extends along the longitudinal direction L of the later track direction, is about 100 to 210 mm, more preferably about 160 to 200 mm, for example about 190 mm. The thickness or height h of the said rail pad 10, 10a- v, 10a-h is about 5 to 14 mm.
The stiffness of the resulting composite rail pad 10, lOa-v, 10a-h is adjusted according to EN 13481-2-C or EN 13146-9 in such a way that the static vertical stiffness in compression (i.e. along the thickness or height h of the rail pad 10, lOa-v, 10a-h) varies in the range from 0 to >2000 kN/mm, but preferably in the range 50 to 200 kN/mm. The ratio of the dynamic stiffness to the static stiffness, i.e. the stiffening of the pad at 10 Hz (tested according to EN 13481-2-C or EN 13146- 9), may be varied most preferably by the properties and/or special geometries of the at least one core damping elements 2, or by the use of special geometries of the pad matrix 1 such as external grooves or studs.
Further example properties of embodiments of rail pads 10, lOa-v, 10a-h according to the present invention are given in the following:
In a first example, the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at 000 Hz < 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 1000 kN/mm, adjusted if necessary using external or internal voids or grooves, and the overall tangent delta measured at l'OOO Hz is greater than or equal to 0.25.
In a second example, the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz < 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 30 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 700 kN/mm, adjusted if necessary using external or internal voids or grooves, and the overall tangent delta measured at l'OOO Hz is greater than or equal to 0.25.
In a third example, the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz < 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 50 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 500 kN/mm, adjusted if necessary using external or internal voids or grooves, and the overall tangent delta measured at l'OOO Hz is greater than or equal to 0.5.
In a fourth example, the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz < 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered corrugated cuboid damping element 2, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 500 kN/mm, adjusted if necessary using external or internal voids or grooves, and the overall tangent delta measured at l'OOO Hz is greater than or equal to 0.25. In a fifth example, the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz < 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa partially encapsulating a cuboid damping element 2 centered in the horizontal plane such that either or both of the top or bottom surfaces of the damping element 2 are flush with the top or bottom surfaces of the rail pad 10, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 1000 kN/mm, adjusted if necessary using external or internal voids or grooves, and the overall tangent delta measured at l'OOO Hz is greater than or equal to 0.25.
In a sixth example, the rail pad 10 has a core-shell morphology comprising an elastic matrix 1, with a static Young's modulus of 40- 100 MPa, a tangent delta at l'OOO Hz < 0.2 and a dynamic (storage) modulus at l'OOO Hz of 80-200 MPa fully encapsulating a centered cuboid damping element 2, or partially encapsulating a cuboid damping element 2 centered in the horizontal plane such that either or both of the top or bottom surfaces of the damping element 2 are flush with the top or bottom surfaces of the rail pad 10, with a static Young's modulus of 1-5 MPa, a tangent delta at l'OOO Hz greater than or equal to 0.5 and a dynamic (storage) modulus at l'OOO Hz of 10-50 MPa wherein said damping element 2 constitutes between 15 and 60 % of total volume of the rail pad 10, such that the static vertical compressional stiffness for a 7 mm thick rail pad with lateral dimensions typical of the state of the art measured according to EN 13481-2-C or EN 13146-9 is in the range 50 to 1000 kN/mm, adjusted if necessary using external or internal voids or grooves that are filled with an elastomeric close-celled or open-celled foam with a static Young 's modulus and bulk modulus very much less than 1 MPa, and the overall tangent delta measured at l'OOO Hz is greater than or equal to 0.25.
All examples are based on the following experimental materials data and data from finite element analysis and modelling:
A homogeneous ethylene vinyl acetate copolymer (EVA, 16 mol% vinyl acetate) (elastic matrix material) shell whose external dimensions are those of the rail pad shown in Figure 1.
Materials data: density 0.95-0.98 g/cc, glass transition temperature - 10 °C, tensile strength 15 MPa, elongation at break 500 %, static Young's modulus (measured at 10 mm/min) 50 MPa
Dynamic elastic properties (20 °C, dynamic tension, strain 1%) are shown in table 1 below:
Figure imgf000048_0001
A homogeneous modified polyisobutylene elastomer (PIB) (high damping material) core placed centrally (center of mass coincides with center of mass of the whole rail pad). Materials data: density >0.92 g/cc, glass transition temperature -30 to -40 °C, tensile strength 10-30 MPa, elongation at break 700 %, static Young's modulus (measured at 10 mm/min) 2.3 MPa.
Dynamic elastic properties (20 °C, dynamic tension, strain 1%) are shown in table 2 below:
Figure imgf000049_0001
A pure (monolithic) EVA rail pad and a pure (monolithic) PIB rail pad as reference materials has been used.
Figure imgf000050_0001
Table 3 (above): Simulation data including relative noise performance with respect to reference EVA rail pad, reference PIB rail pad and a polyurethane (PU) rail pad. Values in bold letters indicate a positive change with respect to the EVA reference rail pad. LIST OF REFERENCE NUMERALS
10, lOa-v, 10a-h rail pad
1, la-v, 1a-h pad matrix (resilient elastic matrix material)
2, 2a-v, 2a-h core damping element (inserted, dispersed, bonded with pad matrix)
3 stiffness modifying element (inserted, optional)
4 cavities/pores (distributed in pad matrix)
5 voids or grooves H height W width L length di first distance (embodiments 10a, b,g) d2 second distance (embodiments 10a, b,g) h3 height of insert t5 depth of groove
W3 width of insert
W5 width of groove
R rail direction

Claims

1. A rail pad (10, lOa-v, 10a-h) comprising: a) a pad matrix (1) comprising a first material and b) at least one damping element (2) at least partially encapsulated or embedded in the pad matrix (1), said damping element (2) comprising a second material, characterized in that the second material of the at least one damping element (2) has a damping factor tan delta > 0.5 at a frequency of 1000 Hz at room temperature.
2. The rail pad (10, lOa-v, 10a-h) according to claim 1, wherein the at least one damping element (2) constitutes between 10 and 90% of the total volume of the rail pad (10, lOa-v, 10a-h).
3. The rail pad (10, lOa-v, 10a-h) according to claims 1 or 2, comprising a single damping element (2).
4. The rail pad (10, lOa-v, 10a-h) according to claims 1 or 2, comprising a plurality of damping elements (2).
5. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, wherein said at least one damping element (2) has a polygonal or circular cross-section in at least one plane, forming cuboids, spheres, ellipsoids, cylinders, or prisms.
6. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, wherein said at least one damping element (2) comprises a plurality of monodispersed or polydisperse particle-like units.
7. The rail pad (10, lOa-v, 10a-h) according to claim 6, wherein said plurality of monodispersed or polydisperse particle-like units have an average dimension comprised between 50 nanometers and 1 millimeter
8. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, wherein the at least one damping element (2) is configured as a sheet or film (11).
9. The rail pad (10, lOa-v, 10a-h) according to claim 8, wherein said sheet or film (11) comprises at least one corrugated surface.
10. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, wherein said at least one damping element (2) comprises of at least one material selected from a non-limiting list comprising polyisobutylene (PIB), crosslinked polyisobutylene (butyl rubber, IIB), polyurethane elastomers (PU), polymer- modified bitumen, polar polymers, such as nitrile, hydrogenated or carboxylated nitrile rubber (NBR, HNBR, XNBR), chlorinated polyolefins (for example, polychloroprene (CR), chlorinated polyethylene or polypropylene, or chlorosulfonated polyethylene), acrylate rubbers (ACM) or epoxidized rubbers (ER), particularly where these have been modified with polar fillers and/or plasticizers or antiplasticizers, conventional vulcanized rubbers such as natural rubber (NR) or synthetic polyisoprenes (PI), polybutadiene (PBD), styrene-butadiene rubber (SBR), styrene- butadiene-styrene black copolymers (SBS), ethylene-propylene diene monomer rubber (EPDM), particularly where these contain high proportions of carbon black or silica fillers and/or plasticizers or antiplasticizers.
11. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, wherein said pad matrix (1) comprises at least one material selected from a non-limiting list comprising crosslinked or non-crosslinked ethylene vinyl acetate (EVA), high density polyethylene (HDPE), polyurethane (PU), crosslinked ethylene- propylene-diene monomer (EPDM) rubber or natural rubber (NR), synthetic cis 1,4-polyisoprene rubber (IR), polybutadiene (PBD), PBD-based copolymers such as styrene-butadiene rubber (SBR) or nitrile-butadiene rubber (NBR), or chloroprene rubber (CR), styrenic block copolymers (SBC), thermoplastic elastomers (TPO) based on rubbery semicrystalline polyolefin copolymers, thermoplastic vulcanizates (TPV) such as isotactic polypropylene- vulcanized ethylene-propylene-diene-monomer (EPDM) blends, copolyester elastomers (COPE), or polyamide elastomers (PAE).
12. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, wherein said pad matrix (1) and/or said at least one damping element (2) comprises at least one of pores, cavities and voids.
13. The rail pad (10, lOa-v, 10a-h) according to claim 12, wherein said pores, cavities and/or voids are sized and distributed so that the pad matrix (1) and/or the at least one damping element (2) is configured as a close-celled or open-celled foam.
14. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, further comprising one or more stiffness modifying element(s) (3) comprised within or onto the pad matrix (1), and separated from the at least one damping element (2).
15. The rail pad (10, lOa-v, 10a-h) according to claim 14, wherein the one or more stiffness modifying element(s) comprises a material that increases the stiffness of at least a portion of the pad matrix (1), relative to the stiffness of the pad matrix (1) itself, by having elastic moduli at least one of which is higher than the corresponding matrix modulus.
16. The rail pad (10, lOa-v, 10a-h) according to claims 14 or 15, wherein the one or more stiffness modifying element(s) comprises a material that decreases the stiffness of at least a portion of the pad matrix (1), relative to the stiffness of the pad matrix (1) itself, by having elastic moduli at least one of which is lower than the corresponding matrix modulus.
17. The rail pad (10, lOa-v, 10a-h) according to claims 14 to 16, wherein the one or more stiffness modifier(s) (3) has or have a polygonal or circular cross-section in at least one plane, forming cuboids, spheres, ellipsoids, cylinders, or prisms.
18. The rail pad (10, lOa-v, 10a-h) according to claim 8 or 9, wherein said sheet includes external studs or ribs or other types of profile on one or both major faces.
19. The rail pad (10, lOa-v, 10a-h) according to any one of the previous claims, wherein said pad matrix and/or said at least one damping element includes internal gaps or holes or grooves (5) or other types of profile.
20. The rail pad (10, lOa-v, 10a-h) according to claim 8, wherein said gaps or holes or grooves (5) or other types of profile have the shape of cylinders with a spherical or ellipsoidal cross-section, and/or prisms with a polygonal cross-section, or grooves (5) with a semispherical or semiellipsoidal or rectangular or triangular cross- section.
21. The rail pad (10, lOa-v, 10a-h) according to claim 19 or 20, wherein said grooves (5) have rectilinear trajectories.
22. The rail pad (10, lOa-v, 10a-h) according to any one of claims 19 to 21, wherein said grooves (5) have regular or irregular zigzag or curvilinear trajectories.
23. The rail pad (10, lOa-v, 10a-h) according to any one of claims 19 to 22, wherein said gaps or holes or grooves (5) or other types of profile of said pad matrix (1) and/or said at least one damping element (2) are either filled with air or with a material different from the one used for the damping element, whose bulk modulus is lower than the bulk modulus of the damping element and/or the pad matrix.
24. The rail pad (10, lOa-v, 10a-h) according to any one of claims 19 to 23, wherein said gaps or holes or grooves (5) or other types of profile of said pad matrix and/or said at least one damping element are filled with a material whose bulk modulus is a least one order of magnitude lower than that of the respective material used for the said pad matrix (1) and/or said at least one damping element (2).
25. The rail pad (10, lOa-v, 10a-h) according to any one of claims 19 to 24, wherein said gaps or holes or grooves (5) or other types of profile of said pad matrix (1) and/or said at least one damping element (2) are filled with an elastomeric close-celled or open- celled foam.
26. A method for production of a rail pad (10, lOa-v, 10a-h) according to one of the preceding claims, comprising the steps of: a) preparing in a preform at least one damping element (2) comprising a material having a damping factor tan delta > 0.5 at a frequency of 1000 Hz at room temperature; b) introducing in a mold the before-prepared at least one damping element (2); and c) performing a multi-step molding process to at least partially encapsulate or embed the at least one damping element (2) with a pad matrix (1).
27. The method of claim 26, further comprising a step of introducing in the mold at least one stiffening modifier (3) before performing the multi-step molding process.
PCT/EP2021/076703 2021-03-15 2021-09-28 Multi-material rail pad and method for manufacturing same WO2022194404A1 (en)

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CN116970229A (en) * 2023-09-23 2023-10-31 河北华密新材科技股份有限公司 Pressure-resistant shrinkage rubber sealing gasket and preparation method thereof

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WO2009094686A1 (en) * 2008-02-01 2009-08-06 Semperit Aktiengesellschaft Holding Damping element
EP2990529A1 (en) 2014-08-20 2016-03-02 Semperit AG Holding Intermediate layer
DE202017104578U1 (en) * 2016-06-16 2017-08-30 Vossloh-Werke Gmbh Elastic element for an attachment point for a rail for rail vehicles and attachment point
KR101847341B1 (en) * 2017-04-17 2018-04-09 김병국 Rail pad of railroad
EP3452659A1 (en) 2016-05-02 2019-03-13 Semperit Ag Holding Rail intermediate layer
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JPH0814325A (en) * 1994-06-24 1996-01-16 Ryobi Ltd Vibration proof pad
WO2005010277A1 (en) * 2003-07-26 2005-02-03 Xuejun Yin Elastic pad
WO2009094686A1 (en) * 2008-02-01 2009-08-06 Semperit Aktiengesellschaft Holding Damping element
EP2990529A1 (en) 2014-08-20 2016-03-02 Semperit AG Holding Intermediate layer
EP3452659A1 (en) 2016-05-02 2019-03-13 Semperit Ag Holding Rail intermediate layer
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116970229A (en) * 2023-09-23 2023-10-31 河北华密新材科技股份有限公司 Pressure-resistant shrinkage rubber sealing gasket and preparation method thereof
CN116970229B (en) * 2023-09-23 2023-12-05 河北华密新材科技股份有限公司 Pressure-resistant shrinkage rubber sealing gasket and preparation method thereof

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