WO2016070905A1

WO2016070905A1 - A reinforcement fabric for reinforcement of an impact resistant or structural composite part

Info

Publication number: WO2016070905A1
Application number: PCT/EP2014/073627
Authority: WO
Inventors: Henk CORNELUS; Veerle Van Wassenhove; Julien Wilkin
Original assignee: Nv Bekaert Sa; Tenneco Automotive Operating Company Inc.
Priority date: 2014-11-04
Filing date: 2014-11-04
Publication date: 2016-05-12
Also published as: CN107206710A; DE112014007131T5

Abstract

A reinforcement fabric (120, 220) for reinforcement of an impact resistant and/or structural composite part comprises a non-metal carrier (124, 224) whereon one or more steel wires (128, 228) are stitched. The steel wires comprise one or more steel filaments of which the tensile strength is larger than 2000 N/mm². The stitching of the steel wires is in a curvilinear trajectory. The reinforcement fabric enables the reinforcement of complex composite parts with steel wire. Contrary to known fabrics with parallel steel cord for reinforcement of composite parts the fabric ensures a positive anchoring of the steel cord at the bends. Also methods for producing the reinforcement fabric are described based on plastic bending of the wire and/or the increased number of stitches per unit length in regions with small radii of curvature.

Description

Title: A reinforcement fabric for reinforcement of an impact resistant or structural composite part.

Description

Technical Field

[0001 ] The invention relates to a reinforcement fabric comprising a non-metal carrier and at least one steel wire held by stitches to said carrier for reinforcement of a structural and/or impact resistant composite part.

Background Art

[0002] Impact resistant and/or structural composite parts (abbreviated to

'Composite Part' in what follows) are for example impact beams, crash boxes for impact beams, A, B or C pillars in cars, seating shells and the like. They are usually made by moulding semi-finished sheets comprising a thermoplastic polymer matrix and reinforcement fibres together in a mould. The reinforcement fibres are usually provided in a fabric form comprising glass or carbon fibre. The fabric can be made of the fibres themselves - as in a weave - or can be held in a non-crimp, unidirectionally or multi-axial fibre laid structure. Recently, attempts are being made to introduce steel wires or cords into Composite Parts as reinforcements.

[0003] For example WO 2005/1 18263A1 describes a textile product comprising at least one layer of non-metal fibres and metal cords - such as steel cords - that are bond to this layer of non-metallic fibres by means of stitches. The metal cords are substantially straight and are parallel to one another. The function of the layer and the stitches is to keep the metal cords in place during consolidation of the molten polymer material in the press moulding process.

[0004] EP0567845A describes a mouldable reinforcement structure with a carrier layer and non-metal reinforcement threads fixed thereto in a curvilinear path. Fixation is by means of stitching threads made of glass, polyamide, polyester or cotton. The product and Tailored Fibre Placement (TFP) method described offers advantages in design optimisation or design freedom. Reinforcement fibres are placed in line with the expected force line distributions. [0005] US 2004/074589 A1 describes a Tailored Fibre Placement (TFP) method wherein reinforcement fibres are sewn onto a substrate using a chemically or thermally meltable fixing thread thereby forming a reinforcement fibre structure. The fixing thread firstly serves to fix the reinforcement fibres on the substrate and is subsequently melted so that the fixing thread disintegrates while pre-fixing the reinforcement fibres without influencing the mechanical properties of the reinforcement fibre structure.

[0006] DE 10 2008 043527 A1 describes a stretchable electrical heating element comprising an elastomeric carrier and a carbon or metal based cord stitched thereon. 'Steel wires' are inter alia mentioned (paragraph [0027]) but without any reference to their make or strength. The function of the carbon or metal based cord is to conduct electricity thereby generating heat. The product described is therefore not suitable for reinforcement of a Composite Part: it stretches and does not impart strength.

[0007] The use of steel cord or steel wire for reinforcement of plastic material (as for example described in WO 2005/1 18263A1 ) offers particular

advantages that are not available when using fibre reinforcement based on the common manmade fibres such as glass fibre, aramid fibre, carbon fibre or similar materials. More particularly steel cord or steel wire reinforcement of a plastic composite part results in an increased ability for energy absorption at impact. Furthermore - unlike the commonly used reinforcement materials -plastic parts reinforced with steel cord or steel wire retain their integrity upon impact. Whereas glass or carbon reinforced impact beams shatter into pieces upon impact - thereby forming a safety risk - steel wire or steel cord reinforced beams remain largely in one - be it heavily deformed - piece.

[0008] However the forms or patterns in which a reinforcement fabric made of steel cord or steel wire can be offered are presently limited in that this is unidirectional as the steel cords are arranged in parallel (for example by stitching WO 2005/1 18263, by warp knitting WO 2009/062764 A1 , by weaving WO 2001/044549, by encasing in a strip WO 2003/076234).

Multidirectional reinforcement can only be obtained by stacking layers of unidirectional reinforcement in different directions. This hampers the use of steel cord or steel wire based reinforcement layers for certain applications where for examples holes have to be made in the composite part, or the composite part has an intricate shape for example a circular or spherical shape. This limitation to a unidirectional reinforcement is a disadvantage for the introduction of steel cord or steel wire as a reinforcement in

Composite Parts.

Disclosure of Invention

[0009] The primary object of the invention is to provide a steel wire based

reinforcement fabric for reinforcement of an impact resistant and/or structural composite part ('Composite Part') that avoids the drawbacks of the prior art. It is a primary object of this invention to provide a steel wire based reinforcement fabric for a Composite Part with an improved design freedom. It is another object of this invention to provide methods to produce such a reinforcement fabric for reinforcement of a Composite Part. Finally Composite Parts comprising the reinforcement fabric with

advantages compared to the known art are described. In short: the inventors succeeded in adapting the embroidering process or Tailored Fibre Placement for use with steel wires.

[0010] According a first aspect of the invention, there is provided a reinforcement fabric for reinforcement of an impact resistant or structural composite part comprising a non-metal carrier and at least one steel wire: the steel wire comprises one or more steel filaments and any one of said filaments has a tensile strength larger than 2000 N/mm². At least one steel wire is held by stitches on said carrier in a curvilinear trajectory.

[001 1 ] According to the present invention, the term 'impact resistant and/or

structural composite part' or 'Composite Part' for short refers to any part wherein structural strength or impact resistance of that part is obtained by the combination of a reinforcement fabric and a polymer matrix. Impact resistant parts are for example comprised in the crash management system of an automotive part such as a front or back impact beam of a car, or the crash boxes behind the impact beam, or a suspension spring cup. Structural composite parts are for example the A, B, C or D pillar of a vehicle, a seat shell, a chair or similar products. It is to be noted that 'impact resistant parts' and 'structural composite parts' are not mutually exclusive: an impact beam is also a structural part and a pillar must also have some impact resistance.

[0012] According to the invention, the term 'non-metal carrier' simply excludes metal as a material for the carrier. The non-metal carrier may be a woven, non-woven or knitted fabric of non-metal fibres such as a scrim ('a fabric with open construction that is used as a base fabric in the production of coated or laminated fabrics' or 'a fabric made with two yarn sheets laid perpendicular to each other and bonded with an adhesive'). Alternatively the non-metal carrier can be a layer, web, film or net. The non-metal fibres can be of natural origin, e.g. cotton, flacks, wool, etc. or manmade fibres e.g. polyamide (6 or 6.6) polyolefin fibres (such as polyethylene or polypropylene), poly-aramid fibres, or glass or carbon fibres or even mineral fibres. Films that can be used are for example polyethylene, celluloid, polyester, or polyamide.

[0013] The function of the carrier is that it must withstand the forces acting on it from the steel wire and it must be easy to stitch on. The carrier must also hold the steel wires at the right place during the moulding process.

Preferably the non-metal carrier has an open structure through which polymer matrix can ingress during moulding. Possibly the carrier can be lost in the processing of the reinforcement fabric. This can be achieved by choosing the composition of the carrier in line with the matrix material that is going to be used. Polyamides for the carrier is therefore a preferred choice if working in a polyamide matrix. Alternatively - when matrix material is only delivered to one side of the reinforcement fabric - the carrier can be 'peeled off after injection moulding and cooling.

[0014] 'Steel wire' itself must be interpreted in the broadest possible way. It can be a single steel filament or the wire can be made up of several steel filaments called a 'steel cord'. Possibly other non-steel fibres can be added to it - in what can be called a 'hybrid steel cord' - but in any case at least one steel filament must be in. 'One steel wire' in the context of this invention, is a steel wire of a single, uninterrupted length. Two or more steel wires are therefore individual steel wires each having an

uninterrupted length that need not be the same. When two or more steel wires are present, the wording does not imply that the steel wires must be of the same make or type. Each of the steel wires maybe of a different type, depending on its needed properties, as explained hereinafter.

[0015] The steel cord can be a 'bundle' of filaments. With a bundle is meant that filaments are kept together in a bunch without intended twisting of the filaments around the axis of the wire. Filaments can be kept together by means of a binder filament stitched around it or a wrapping wire (a wrapping wire makes complete turns around the bundle, a stitched wire makes a back and forth movement around the wire). Alternatively the filaments can be held together by a polymeric coating or a glue. A preferred alternative is if the bundle of filaments is held by the stitch that holds the steel wire to the carrier.

[0016] The steel wire can also be in the form of 'a strand'. In that case filaments are twisted around the centre of the wire with an intended lay length. Either all filaments receive the same lay of which typical examples are compact cords (wherein all filament diameters are equal), Warrington or Seale strands (wherein filaments fit together in a certain pattern).

Alternatively strands can be made in layers wherein a layer of filaments is twisted with a layer lay length around a centre filament or precursor strand resulting in a layered cord (for example a 3+9+15 cords wherein a core strand of 3 filaments twisted together is surrounded by a layer of 9 filaments and finally with a layer of 15 filaments).

The steel wire can be a steel rope. A steel rope is a steel cord comprising steel strands that are twisted around each other. For example a 7x7 steel cord consists of a steel core strand of 7 filaments around which 6 strands each comprising 7 filaments are twisted with a rope lay length.

[0017] The steel wire as a whole can be coated with an organic coating prior to stitching to the non-metal carrier. This may be useful to additionally isolate the steel wire from the surroundings or to completely integrate the steel wire in the part. Possible coatings are polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyurethane (PU), polysulfone (PES), ethylene tetrafluoroethylene (ETFE) and others.

Preferred coatings are those that are at least compatible or identical to the matrix material of the Composite Part. The process of coating can be performed by means of extrusion, electrostatic coating or any other known technique. Preferably the organic coating fully penetrates the steel wire to prevent the formation of channels in the steel wire when it is composed of three or more filaments.

[0018] In general steel wires in this invention contain less than a hundred steel filaments, and in most cases even less than fifty and preferably less than or equal to 12 steel filaments. A preferred embodiment is when the steel wire consists of a single steel filament.

[0019] The base material of the wire used is plain carbon steel. A typical plain carbon steel composition has a minimum carbon content of 0.65%, a manganese content ranging from 0.40% to 0.70%, a silicon content ranging from 0.15% to 0.30%, a maximum sulphur content of 0.03%, a maximum phosphorus content of 0.30%, all percentages being

percentages by weight. There are only traces of copper, nickel and / or chromium. With a higher carbon content a higher tensile strength can be achieved. The metallographic structure of the base material is fine perlitic with no traces of bainite or martensite.

[0020] Alternatively the wire used can have a plain carbon composition with a carbon content between 0.40 to 0.85 %, a silicon content between 1 .0 and 2.0 %, a manganese content between 0.40 to 1 .00 %, chromium being present in a range between 0.0 to 1 .0 %, with a total concentration of below 0.025 % of phosphorous and sulphur. The remainder is iron and unavoidable impurities with the further limitation that the concentration of alloying elements such as nickel, vanadium, aluminium, or other micro- alloying elements each remain below a concentration of 0.2 %. Again all percentages are understood to be percentages by weight. The

metallographic structure of the base material shows a volume percentage of retained austenite of between 4 to 20 % while the remainder is tempered primary martensite and untempered secondary martensite. Such a starting wire obtained by quenching and subsequent partitioning (Q&P) shows a high initial tensile strength that increases rapidly by work hardening (see WO 2013/041541 ).

[0021 ] Also stainless steel wires can be used. Stainless steels contain a minimum of 12%Cr and a substantial amount of nickel. More preferred stainless steel compositions are austenitic stainless steels as these can easily be drawn to fine diameters. The more preferred compositions are those known in the art as AISI 302 (particularly the 'Heading Quality' HQ), AISI 301 , AISI 304 and AISI 314. 'AISI' is the abbreviation of 'American Iron and Steel Institute'.

[0022] By work hardening - e.g. by wire drawing and/or cold rolling - the tensile strength of the steel filament is further increased to above 2000 N/mm², preferably larger than 2300 N/mm², or even more preferably larger than 2700 N/mm², or even above 3000 N/mm². Currently steel filaments with tensile strengths above 3300 N/mm² are common in tyre cord, while the maximum is now around 4000 N/mm². The finer the filaments are, the larger their tensile strength can be. The filaments are individually drawn. The case of so-called 'bundle drawn' filaments is herewith explicitly excluded. 'Bundle drawn' filaments are filaments that are drawn in a group through a single die and are thereafter separated.

[0023] The tensile strength of the steel filaments of the steel wire is the basic parameter determining the strength of the reinforcement fabric. Using a tensile strength below 2000 N/mm² necessitates more steel, hence more weight, in order to reach the same overall strength of the Composite Part. The purpose of using Composite Parts is to reduce weight, not to increase it. By using higher tensile steel wires one can reduce weight.

[0024] The wire cross section of the one or more filaments in the steel wire has a surface area between 0.008 mm² and 1 .14 mm². The cross section may or may not be round. Not round cross sections are for example oblong shapes, dogbone or even H-profile sections. The use of non-round profiles may be advantageous in cases where the stiffness of the wire in one direction must be larger than in another direction. The equivalent diameter of the steel filaments - i.e. the wire with a round cross section having an equal cross sectional area of that of the wire with the not round cross section - is thus between 0.101 mm and 1 .20 mm. More preferably the equivalent diameter (number between brackets is cross sectional surface area) is between 0.120 mm (0.01 1 mm²) and 0.30 mm (0.070 mm²) and even more preferred is if it is between 0.150 (0.018 mm²) and 0.25 mm (0.049 mm²). [0025] Possibly the individual steel filaments are coated with a functional coating that for example prevents corrosion (by means of a zinc or zinc alloy coating), enhances adhesion to the polymer matrix (for example by applying an organic coating layer such as an organo functionalised silane, organo functionalised titanate and an organo functionalised zirconate) or combines both.

[0026] The steel wire is held to the non-metal carrier by means of stitches of a yarn. The function of the stitched yarn is to hold the steel wire one sided to the non-metal carrier. Many machine stitches can be applied but single or double yarn stitches will generally do the job although three or four yarn stitches are also possible. Preferred stitches are zig-zag lockstitch or zigzag chainstitch (double yarn, ISO 4915 standard, numbers 304 and 404 respectively). Other possible stitches are the needle top coverstitch (ISO 4915, number 406, 3 yarns), or a needle chainstitch with cover thread (ISO 4915, number 408, 5 yarns).

[0027] Yarns are chosen in function of holding force and polymer matrix. In

general they need to be strong, flexible, thin and smooth. Examples are polyamide, polyester, polypropylene, poly tetrafluoroethylene, or elastane although other natural fibres like silk, cotton and others are likewise possible.

[0028] The steel wire is laid in a 'curvilinear trajectory'. A 'curvilinear trajectory' can be defined as any trajectory or path that at least contains a section with a non-zero curvature 7c' (expressed in mm^"1). A straight line has zero curvature. The curvature at a point along the curve is the inverse of the 'radius of curvature' at that point. The 'radius of curvature' is the radius of a circle osculating to the wire path at that point on the path. With 'osculating' is meant that zero, first and second order derivatives of circle and path are equal at that point. The curvilinear trajectory is substantially in line with the forces acting in or expected to act in the Composite Part so as to reinforce the polymer matrix maximally.

[0029] Known tailored fibre placement methods work with reinforcement fibres of carbon, aramid or glass fibre rovings that contain many thousands of individual filaments. The individual filaments are very fine (from 5 m to 10 μιτι for carbon rovings, 5 μιτι to 25 μιτι for glass rovings) which makes the manipulation of the rovings or cords very easy as they do not resist bending at all.

[0030] Steel filaments as subject of this invention are much more difficult to

handle in this respect. When mentioning 'bending' of a steel wire comprising one or more steel filaments one must discriminate between two different notions:

There is the 'stiffness' or 'bending rigidity' of the filament which is a measure for the resistance to bending. The stiffness (in Nmm²) for a round wire is End /64 wherein '£" is Young's modulus of the material (in N/mm²) and 'd' is diameter of the filament (in mm).

[0031 ] In a roving - as the individual fibres glide over one another - the stiffness increases linearly with the number of fibres. For currently known reinforcement rovings this stiffness is negligible due to the extreme thinness of the filaments. As a result the rovings can easily be laid by a roving pipe just before the stitching head of the embroidery machine as is known in tailored fibre placement.

[0032] This is not so for steel wires of the invention comprising thick filaments whereof the stiffness increases with the fourth power of the diameter. More moment must be exerted on the wire to bend it to a certain curvature, as the bending moment is equal to the product of stiffness and curvature. The higher bending moment of the filaments inhibits the easy laying of the reinforcement, and special measures have to be taken in the process to overcome this bending stiffness.

[0033] Next to the stiffness of a steel filament there is the notion of 'bendability'.

This relates to the plastic deformability of the steel wire. When a non-zero curvature is applied to a steel filament it will spring back after removal of the bending moment. When the applied curvature 'k_a' is sufficiently large (i.e. for sufficiently small bending radii) some curvature will remain after the removal of the bending moment: this is the residual curvature 7c_r' due to the plastic deformation of the wire material. The difference between the two: 'k_a - k_r' applied minus residual curvature is called 'spring back'. The elastic-plastic bending theory of beams learns that this spring back is depending on the cross section shape and diameter of the wire, the yield stress and the modulus of the material according wherein 'η' is a dimensionless form factor (equal to about 1 .7 for a round cross section and 1 .5 for a rectangular section), '£" is the elongation modulus of steel, 'R' is half the diameter of the wire and 'σ_ρ' is the 'yield stress' of the material. Reference to the elastic-plastic bending theory is merely to illustrate what parameters are of importance and should not be relied on to obviate the invention in any way.

[0034] The yield stress is that stress (in N/mm²) at which permanent elongation of the wire in a tensile test occurs. Conventionally the permanent elongation is set to 0.2% to determine the yield stress and is called the Rp0.2 point on a tensile curve. So the higher the yield stress and the smaller the diameter of the wire, the more difficult it becomes to give the wire a residual curvature or permanent bend.

[0035] The yield stress of a steel filament depends on the processing (work

hardening or thermal treatment) and the material composition of the steel filament (high carbon vs low carbon) and is for the types of materials envisaged in this application (high carbon, high degree of working) larger than at least 65 % of the tensile strength of the steel filament, or above 75% or even above 85% of the tensile strength of the wire. Very far drawn, hence fine, wires have a yield stress to tensile strength ratio above 95% and are very difficult to permanently bend as they have a high yield stress in combination with a small diameter. Representative values for yield stresses are therefore at least 1300, 1500, 1750, 1900, 2050, 2300, 2450, 2600, 3000, 3400 and 3800 N/mm² wherein the yield stress is in any case lower than the tensile strength of the steel filament.

[0036] The increased stiffness and difficult bendability of the steel wire leads to increased stress in the reinforcement fabric. However by proper selection of diameter, number of filaments (influencing the stiffness and bendability) and yield stress (influencing the bendability) the inventors were capable to obtain processable reinforcement fabrics with steel wire. [0037] In order to be able to align the steel wires in the fabric bends with small radii of curvature are needed. In the inventive fabric curvilinear trajectories where locally a radius of curvature that is smaller than 70 times the equivalent diameter 'd_max' (in mm) of the filament in the wire with the largest cross sectional area. Even radii of curvature smaller than 50 times, or even smaller than 35 times that maximum equivalent diameter turned out to be possible.

[0038] In order to hold the stiff steel wire on the carrier one can increase the

number of stitches at loci where the radius of curvature is small (where the curvature is large) and decrease the number of stitches at loci where the radius of curvature is large (i.e. curvature is small).

[0039] Alternatively or additionally the steel wires in the reinforcement fabric are plastically bent. With 'plastically bent' is meant that when stitches are removed and the steel wire is freed the steel wire remains in a deformed state. As mentioned above, a permanent or residual curvature can be given to a steel wire by applying a sufficiently large curvature. Plastic bending may be needed in cases where the bending moment in the steel wire results in a fabric that does not remain in one plane. It is to be noted that rovings of carbon fibres or glass fibres are never plastically bent when removed from such reinforcement fabric.

[0040] Preferably but not essential for the invention, the reinforcement fabric

remains 'open'. With 'open' is meant that during injection moulding, the polymer can pass through the reinforcement fabric. This implies that the non-metal carrier must be open and that the steel wires have to be sufficiently far apart from one another to let the polymer flow through.

[0041 ] By laying the steel wire according a predefined curvilinear trajectory one can circumscribe one or more specific areas on said carrier. In this way the presence of steel wire in certain areas is avoided. This inventive reinforcement fabric therefore allows for example punching of holes or cutouts in the Composite Part at specific areas without the steel wire being damaged. The integrity of the Composite Part is thereby greatly improved and the cutting of the steel wire avoided. In general punching of known fabrics comprising steel wires laid parallel results in a loss of integrity of the fabric as each hole leads to many cut steel cord ends. Also punching of the steel wire leads to excessive wear of the punching tool. The invention therefore offers - in addition - a good solution to this problem.

[0042] On many instances reinforcement in more than one direction of the

structural reinforcement part will be needed. It may therefore be necessary that a steel wire is first laid in a trajectory primary in a first direction and another steel wire is subsequently laid in a second direction that is oblique to the first direction. In this way the steel wires will cross at points of the trajectory that are called 'crossovers'. At a crossover, the fabric is

somewhat thicker as the steel wires are laid on top of one another.

Possibly a steel wire can cross itself which is called a 'self-crossover'. Also possibly more than two wires can cross at the same locus, but such situation should be avoided as this leads to instability. For example when three steel wires cross at the same point, the middle wire may shift upon injection moulding.

[0043] A second aspect of the invention is about a Composite Part such as an impact resistant and/or structural composite part that comprises the above described reinforcement fabric that is embedded in a polymer matrix.

Different with prior art Composite Parts is that the number of steel wires in said reinforcement fabric is less than or equal to ten. As the wires can be laid according a specific trajectory the mandatory parallel arrangement of many steel wires (more than ten) as in prior art steel cord fabrics is avoided. The result is that also at the bends, the steel cords are positively anchored into the polymer matrix. This is not the case in prior art fabrics where the many ends of the steel cord are not anchored in the polymer matrix.

[0044] The polymers that can be used in the Composite Part are known and are a thermoplastic or thermoplastic elastomer polymer material. More preferred, the polymer is selected from the group consisting of polyester,

polyurethane, polypropylene, polyethylene, polyamide, polyethylene terephtalate, polybutylene terephtalate, polycarbonate, polyphenylene oxide as well as blends of these materials, or thermoplastic elastomers, e.g. polyamide- or polyolefin- based thermoplastic elastomers such as polyesteramides, polyetheresteramides, polycarbonate-esteramides or polyether-block-amides. [0045] Particularly interesting thermoplastic polymers are in-situ polymerisable thermoplastic materials. These materials can be handled in a pre-polymer state (in the form of a liquid or a powder or as pellets) and once in the mould react to the final polymer after initiation with an energy input (heat or electromagnetic radiation). Typical examples are caprolactam (reacting to polyamide 6) or laurocaprolactam (reacting to polyamide 12), mixtures of both, or any of the pre-polymers of the polymers mentioned in the previous paragraph.

[0046] Alternatively the polymers can be thermosetting polymers such as

polyester resin, epoxy, vinylester. Possibly the polymers are provided in a sheet moulding composite i.e. the reinforcement fabric is pre impregnated with the polymer or the pre-polymers of the polymer prior to being inserted into the mould.

[0047] A preferred embodiment of the Composite Part comprises also openings that are circumscribed by at least one steel wire trajectory. At such opening the Composite Part can be held strongly by a fastening means such as for example a bolt, rod or a safety belt as the steel wire forms a loop around the fastening means.

[0048] According a third aspect of the invention, methods are offered that

describe how the reinforcement fabric can be made.

According a first preferred embodiment one starts with a non-metal carrier as described in paragraphs [0012] to [0013] above. Further a steel wire comprising one or more steel filaments as described in paragraphs [0014] to [0025] is provided. The steel filaments have a cross section with a cross sectional area between 0.008 mm² and 1 .14 mm² and a yield stress of at least 1300 N/mm². Subsequently the steel wire is stitched onto the carrier according a curvilinear trajectory. Specific about the method is that the wire is plastically bent prior to being stitched to the non-metal carrier. There are a number of ways in which this can be accomplished.

[0049] A first way is that a bend is applied with the appropriate applied curvature - appropriate in that the residual curvature remaining is close to the planned curvilinear path - by bending the steel wire over a tool. The tool can be a pin, or a set of pincers, or a bending clamp. The tool can be incorporated in the stitching head and the bending of the steel wire is then applied while the steel wire is being fed for stitching .

[0050] An alternative second way is that the steel wire is first laid out over a frame with pins. The pins have the appropriate layout and reproduce the desired curvilinear trajectory. The steel wire is tensioned till the desired curvature is reached at the bending pins. Thereafter the wire is wound up again. The spool is fed to the embroidery machine and - as the wire has obtained the necessary permanent bends beforehand - the steel wire gives little resistance when there is a bend in the curve while stitching and lays itself accordingly.

[0051 ] A variant to this implementation is that the steel wire is wound from one spool to another and along the length of the steel wire appropriate bends are induced on the wire according to the planned curvilinear trajectory.

[0052] In a third alternative way, the bending can be eased by locally heating up the wire. Although such heating up may result in a locally lower tensile strength the integrity of the steel wire is not compromised.

[0053] In a second preferred embodiment of the invention the method comprises the following steps:

• Providing a non-metal carrier of the type as described in paragraph

[001 1 ] to [0012];

• Providing a steel wire that comprises one or more steel filaments, said filaments having a convex cross section with a cross sectional area between 0.008 mm² and 1 .14 mm² and with a yield stress larger than 1300 N/mm².

• Stitching the steel wire to the carrier according a curvilinear trajectory.

In the method the number of stitches per unit length along said curvilinear trajectory is lowered at loci with a large radius of curvature and increased at loci with a small radius of curvature.

[0054] Typically the number of stitches per cm 'S_m' scales lineary with the

curvature 'k(s)' (in mm^"1)at distance 's' along the trajectory and is between bounds : 0.5 + 15 x d_max x k(s) < S_m < 2 + 140 x d_max x k(s) wherein 'd_max' (in mm) is the largest equivalent diameter of the steel filaments in the steel wire. According the experience of the inventors this number of stitches is sufficient to hold the steel wires according this invention in place.

[0055] Stitching the steel wire to the non-metal carrier is done by an embroidery machine adapted with a reinforcement supply means. The embroidery machine can either be an embroidery machine with moving head or an embroidery machine with a moving table, or a combination of both.

Alternatively the stitching head can be implemented in a robotic arm.

Brief Description of Figures in the Drawings

[0056] Figure 1 a shows a first application of the invention in a car seat for a child

[0057] Figure 1 b shows the prior art reinforcement fabric

[0058] Figure 1 c shows the inventive reinforcement fabric

[0059] Figures 2a and 2b show the application of the inventive reinforcement fabric in another application: a suspension cup.

[0060] Figure 3a shows the use of the reinforcement fabric in a B-pillar as used in a car.

[0061 ] Figure 3b shows the stitching pattern to obtain the reinforcement fabric for use in the B-pillar.

[0062] Figure 4a shows a lay out of the reinforcement fabric for use in the

reinforcement beam in car door.

[0063] Figure 4b shows a method to induce the necessary bends in the steel wire.

[0064] Figure 4c shows the deformed steel wire prior to stitching it on the carrier.

[0065] Numbers ending on '20' relate to the inventive reinforcement fabric,

numbers ending on '24' refer to the non-metal carrier, numbers ending on '26' relate to the stitches that hold the steel wire referred to with numbers ending on '28'. Mode(s) for Carrying Out the Invention

[0066] Table I is a table of materials that are used in rovings for tailored fabric placement compared to steel wire:

Table I

[0067] It is clear from the table that rovings made of carbon fibre, E- or S- glass fibre are much easier to manipulate and bend then steel wire although this steel wire contains much less filaments. The influence of the diameter of the fibre is in this respect all overwhelming due to the dependency of the stiffness on the fourth power of the diameter. Modulus and number of filaments play a subordinate role in this. The table illustrates that the fibre placement with steel cord is totally different from fibre placement with known rovings.

[0068] Figure 1 a illustrates a first implementation of the invention. It shows a car seat for a child 100 made by injection moulding wherein the bottom part is reinforced with a fabric 1 10/120 thereby forming a Composite Part.

[0069] In a prior art reinforcement fabric 1 10 shown in Figure 1 b, a fabric is made by weaving textile yarns 1 16 in warp with parallel steel cords 1 14 in weft. The fabric is made in a rectangular shape and the final shape of the reinforcement fabric 1 10 is later cut out by punching and stamping or laser cutting. In this way also holes are 1 12, 1 12' and 1 12" are made in the fabric where later fixtures can be inserted (to hold the seat to the car). The process of cutting leads to many steel cord ends and a considerable loss of material. Also the presence of the holes compromises the integrity of the fabric as steel cords tend to become loose.

[0070] Figure 1 c shows the inventive reinforcement fabric 120 that comprises a non-metal carrier 124 and a single steel wire 128. The single steel wire is laid in a curvilinear path thereby avoiding the areas where holes are foreseen: 1 30, 1 30', 1 30". The steel wire is stitched to the carrier by stitches 1 26 that are denser in the loci where the curvature is large and less dense in the sections were the steel wire is substantially straight (the osculating circles at minimal radius of curvature are drawn at the bends in dashed lines 1 27).

[0071 ] Particulars for this first embodiment were:

• Non-metal carrier: a polypropylene open scrim.

• Steel wire: 3x0.265+9x0.245 steel cord consisting of 1 2 filaments twisted around each other with a 14 mm lay length. The filaments are hot dip galvanised prior to single filament drawing and have filaments with a tensile strength of 2700 N/mm² and a yield stress of 2045 N/mm².

• Stitch yarn used is a polypropylene yarn and the stitch is a single yarn interlock. The number of stitches varied between 2 stitches per cm in the parts with zero curvature (straight sections) to 4 stitches per cm in the 90° bends with curvature 1 /6 mm^"1 and to 1 0 stitches per cm in the 1 80° bends with curvature 1 /3 mm^"1.

The reinforcement fabric could be made with very little loss of material and maintains its integrity well during injection moulding. The fabric allowed for easy passage of the injected polymer due to its openness.

[0072] A second application of the reinforcement fabric is shown in Figure 2a

where the fabric 21 0/220 is integrated in a suspension cup of a car 200. The prior art fabric 21 0 consisting of warp knitted steel cord held by a yarn in weft results in a large loss of material and a reduced fabric integrity after cutting. Figure 2b shows the inventive reinforcement fabric prior to injection moulding. The fabric comprises a non-metal carrier 224 on which steel wire 228 is stitched by means of stitching yarn 226. The path followed is curvilinear and circumscribes the central opening 230 in a spiral way. The non-metal carrier was a polyamide open scrim, the yarn used was also made of PA both being compatible with the matrix of the suspension cup. The stitch was a double yarn zig-zag lock stitch. The steel wire was a single filament of diameter 0.95 mm of the quenched and partitioned type having a tensile strength of 2300 N/mm² and a yield stress of 1518 N/mm². Such a wire is particularly suited to make in a preform prior to stitching due to its combination of high diameter with low yield point. The number of stitches was about 2 per cm. By introducing the reinforcement fabric during moulding with polyamide an improved suspension cup could be made. Inventors assert that the reinforced suspension cup could withstand the impact of a broken suspension spring.

[0073] To be noted is that when the steel wire is removed from the carrier by

cutting the stitches, the steel wire assumes a shape very near to the spiral shape in the reinforcement fabric. This indicates that the steel wire has been plastically bend and is indicative for the inventive reinforcement fabric.

[0074] In a third embodiment the inventive reinforcement fabric was used in an injection moulded part for reinforcing the B-pillar of a car thereby forming a Composite Part as shown in Figure 3a and 3b. The part 300 has a complex shape. The steel wire 328 must follow an intricate path in order to reinforce the part well. Next to that a second steel wire 328' is cross laid and stitched on top of the first one.

[0075] When laid open the resulting curvilinear trajectory is shown in Figure 3b.

The carrier used was an organosheet (PA6 polymer sheet reinforced with woven glasfibre), the stitch was a double yarn zig-zag lockstitch made with yarn 326 of PA6 . Both steel wires 328 and 328' were a steel cord of make 0.37+6x0.33, brass coated, the cord being subsequently coated with PA by means of extrusion. The detail shows that in the neighbourhood of the turnovers the number of stitches is increased from 1 .5 per cm in the straight sections to 10 per cm in the sections having a radius of curvature of 3 mm. Hence the radius of curvature is about 8 times the diameter of the largest filament in the steel wire.

[0076] Figure 4a, 4b and 4c illustrates a method to make the inventive

reinforcement fabric. The lay out of the reinforcement fabric 402 is shown in Figure 4a and it is intended to be used in a side impact beam of a car door (a Composite Part). The trajectory of the steel wire 428 is such that it circumscribes the areas 410, 410', 410", 410"' where holes will be punched in the polymer for attaching the side impact beam to the door. The single steel wire 428 meanders from one end of the beam to the other end. The steel wire is stitched to the carrier 424 by means of stitching yarn 426.

[0077] Before the steel wire 428 is stitched on the non-metal carrier 404 it is

preformed over a pin board as shown in Figure 4b. The pin board 420 has pins with different radii 422 (422', 422", 422"',...) and 423 (423',...). The pins are placed such that the distance between the pins corresponds about to the distance between bends in the lay out scheme. The radii of the pins - that correspond to the inverse of the applied curvature 'k_a' - are chosen such that the resulting radius of curvature more or less

corresponds to the radius of curvature in the lay-out scheme. The one steel wire end is fixed to the pin board while the other end is pulled with a force 'F' at least sufficient to make the steel wire follow the radii of the pins.

[0078] When now removed from the board, the wire 428 will reflect the intended trajectory of the steel wire in the reinforcement fabric as shown in Figure 4c. The preformed steel wire can now be wound on a spool 430 and subsequently fed to an embroidery machine. When the embroidery machine follows the trajectory of the lay out scheme, at the bends the preformed steel wire can be laid without having to induce an excessive bending moment.

[0079] By applying these inventive principles the inventors succeeded in adapting the tailored fibre placement technique also for steel wires. As mentioned the use of steel wires then poses particular problems which by application of this invention are overcome.

Claims

1 . A reinforcement fabric for reinforcement of an impact resistant and/or

structural composite part comprises a non-metal carrier and at least one steel wire held by stitches to said carrier, wherein said steel wire comprises one or more steel filaments,

characterised in that

said one or more steel filaments have a tensile strength larger than 2000 N/mm² and said at least one steel wire is held by stitches on said carrier in a curvilinear trajectory.

2. The reinforcement fabric according to claim 1 wherein the number of steel filaments in said steel wire is less than hundred.

3. The reinforcement fabric according to any one of claim 1 or 2 wherein the cross section of any one of said filaments has a convex shape with a cross sectional area larger than 0.008 mm² and smaller than 1 .14 mm².

4. The reinforcement fabric according any one of claims 1 to 3 wherein said steel filaments have a yield stress of at least 65% of the tensile strength of said steel filaments.

5. The reinforcement fabric according to any one of claims 1 to 4 wherein said curvilinear trajectory locally has a radius of curvature that is smaller than 70 times the equivalent diameter of the filament with the largest cross sectional area in said steel wire.

6. The reinforcement fabric according to any one of claims 1 to 5 wherein

more stitches per unit length are present in the trajectory at loci with small radii of curvature than in the trajectory at loci with large radii of curvature.

7. The reinforcement fabric according to any one of claims 1 to 6 wherein said steel wire is plastically bent.

8. The reinforcement fabric according to any one of claims 1 to 7 wherein said steel cord trajectory remains open such that polymer can pass through said reinforcement fabric.

9. The reinforcement fabric according to any one of claims 1 to 8 wherein said trajectory circumscribes specific areas on said carrier.

10. The reinforcement fabric according to any one of claims 1 to 9 wherein said trajectory of said at least one wire comprises crossovers, said crossovers being self-crossovers of the same one steel wire or crossovers of two different steel wires.

1 1 .A composite part comprising the reinforcement fabric according to any one of claims 1 to 10 embedded in a polymer matrix

characterised in that

the number of steel wires in said reinforcement fabric is less than or equal to ten.

12. The composite part according to claim 1 1 , said structural composite part comprising openings, said openings being circumscribed by said at least one steel wire trajectory.

13. A method to produce a reinforcement fabric for reinforcement of a

composite part comprising the steps of

- Providing a non-metal carrier;

- Providing a steel wire, said steel wire comprising one or more steel filaments , said steel filaments having a convex cross section with a cross sectional area between 0.008 mm² and 1 .14 mm² and a yield stress of at least 1300 N/mm² ;

- Stitching said steel wire onto said carrier according a curvilinear trajectory;

characterised in that

said steel wire is plastically bent prior to being stitched to said non-metal carrier.

14. The method claim according to claim 13 wherein said bending is performed by bending the steel wire while being fed for stitching.

15. A method to produce a reinforcement fabric for reinforcement of a

composite part comprising the steps of: - Providing a non-metal carrier;

- Providing a steel wire, said steel wire comprising one or more steel filaments, said steel filaments having a convex cross section with a cross sectional area between 0.008 mm² and 1 .14 mm² and a yield stress of at least 1300 N/mm²;

characterised in that

the number of stitches per unit length along said curvilinear trajectory is lowered at loci with a large radius of curvature and increased at loci with a small radius of curvature.