Classifications

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Definitions

• the present invention relates to a micro-lattice and, more particularly, to a micro-lattice damping material and a method for repeatabie energy absorption.
• the present invention is directed to a material that. can. be used for damping, such as acoustic damping and vibration damping.
• Acoustic damping or quieting is a process by which components, such as machinery, is made quieter through acoustic absorptio to minimize the acoustic impacts of such components.
• Acoustic absorption is traditionally accomplished using porous materials, such as open-cell foams, fibrous materials, carpets and draperies. Such porous materials absorb acoustic energy by oscillation of the air molecules in the interconnec ted pores (air friction). This mechanism is fundamentally different from the buckling mechanism used in the present invention and causes the damping to be a strong function of frequency (small absorption at low frequencies) and material thickness. Furthermore, closing the pores (e.g., by painting) reduces the effectiveness of such traditional acoustic absorption materials.
• viscoeiastic polymers These materials absorb energy by polymer chains sliding under stress, which is responsible for the viscous flow.
• the efficacy of viscoeiastic polymers is strongly dependent on temperature and, therefore, viscoeiastic polymers exhibit high damping coefficient only in a small temperature range (see figure below ). The consequence of this is either poor performance at temperature extremes or the use of blends of polymers which provides less performance across a broader temperature window.
• the present invention relates to a micro-lattice and., more particularly, to micro-lattice damping material and a method tor repeatable energy absorption.
• the present invention is operable to provide high damping, specifically acoustic, vibration or shock damping, by utilizing the energy absorption mechanism of hollow tube buckling (as provided for by the micro-lattice).
• the damping material is a micro-lattice formed of a three-dimensional interconnected network of hollow tubes.
• the hollow tubes are formed of a material and have a wail thickness and a diameter, such thai a wall ihickaess to diameter ratio is less than 3£ y , where £ v denotes a yield strain material property of the material forming the hollow tubes,
• the hollow tube diameter is between 10 ⁇ and 10 era.
• the hollow tubes are formed of a material selected from a group consisting of metal, ceramic, and a polymer.
• a constraining layer is attached with the micro- lattice, with the micro-lattice being eonneetable with an object to be dampened,
• the micro-lattice includes a damping coefficient (tan6) that is greater than 0.05.
• the micro-lattice has a density smaller tha 0.1 e/enr .
• the micro-lattice is partially compressed between two materials such that the micro-lattice is pre-loaded with strain.
• the micro-lattice is preloaded to strains between 3% and 50%.
• the micro-lattice has a density of 10 rag/cm or less.
• micro-lattice is adapted to provide for
• the micro-lattice is attached to one or more face sheets,
• the invention is directed to a method for
• damping through repeatahle energy absorption comprising acts of receiving a load in a micro-lattice having a network of interconnected hollow tubes (the load causing elastic buckling of the hollow tubes and/or nodes where the tube intersect); and removing the load, resulting in the micro-lattice decompressing, whereby upon removing the load, the micro- lattice recovers its original shape.
• the invention is directed to a constrained layer
• damper comprising a micro-lattice formed of a three-dimensional interconnected network of hollow tubes, the micro-lattice attached with an object to be dampened; and a constraining layer attached with the micro- lattice such that the micro- lattice is sandwiched between the object to be dampened and the constraining layer
• the invention is directed to an amplitude selective damping material, comprising a micro-lattice that requires a threshold stress to trigger buckling and concomitant energy absorption.
• the invention is directed to an anisotropic damping material, comprising a micro-lattice formed to provide anisotropic damping properties.
• the damping material includes a micro-lattice formed of a three-dimensional interconnected network- of hollow tubes and two layers of material, with the micro-lattice being partially compressed between the two layers such that the micro-lattice is pre-loaded with strain.
• the present invention also includes methods tor forming and using the damping materials described herein.
• FIG. LA is a schematic illustration of a damping .mechanism according to the principles of the present invention, depicting hollow tube buckling that is reversible and absorbs energy;
• FIG. IB is a chart showing the stress and strain during compression and release of roicrolattiee material consisting of an array of hollow tubes, illustrating energy absorption of the hollow tubes as the buckle;
• FIG. 2 A is an illustration of a micro-lattice damping material
• FIG. 2B is an illustration of a micro- lattice dampin material
• FIG. 3 is an illustration depicting a method for forming a ⁇ micro-lattice material
• FIG. 4A is an illustration of a micro-iattice sample prior to
• FIG. 4B is an illustration of the micro-lattice sample, depicting the sample at -10% compression
• FIG. 4C is an illustration of the micro-lattice sample, depicting the sample at 50% compression
• FIG. 4D is an illustration depicting the micro-lattice sample after the compression load is removed, illustrating that the micro-lattice recovers approximately 98.6% of its original height and resumes its original shape;
• FIG. 4E is an optical image of a unit cell of the micro-lattice, in an unloaded or uncompressed condition;
• FIG, 4F is an optical image of the unit cell, depicting the unit ceil as accommodating compressive strain by buckling at its node;
• FIG. 4G is a scanning electron microscopy (SE. ) image of a node before compression testing
• FIG. 4H is an SEM image of the node after six compression cycles at 50% strain
• FIG. 5A is a graph illustrating a stress-strain curve measured in
• FIG. SB is a graph of illustrating how stifrhess and strength initially diminish with cycle number and then stabilize;
• FIG , 5C is a graph illustrating stress-strain curves of the first two
• FIG, 5D is a graph illustrating stress-strain corves of the compression of a sample with 43mg cc (L; 1050 pm, D: 150 ⁇ , t; 1400 ran);
• FIG. 5E is a graph illustrating an effect of the aspect ratio t/D of wall thickness (t) over diameter (D) on Ni-7%P micro- lattice compression behavior;
• FIG. 6 is a graph illustrating the dampin coefficient (tan 5) and strain vs. normal force (preload) of a "virgin" Ni-7%P micro-lattice with a density- 1 ntg cnr > in a compression DMA test at frequency 55 1 Hz and amplitudeTM5pm;
• FIG. 7 is a graph illustrating the damping coefficient vs. strain of a pre-compressed Ni-7%P micro-lattice with a density-! 2mg/cm '> in a compression DMA test at frequency-! Hz and three different amplitudes;
• FIG. 8 is a graph illustrating the damping coefficient and shear
• FIG. is a graph illustrating the dampin coefficient vs. frequency of a i ⁇ 7%P micro-lattice with a density --20mg/crrr in a shear DMA test ai two different amplitudes and two different pre-compression strains;
• FIG. 10 is a graph illustrating acoustic absorption of micro-lattice compared to acoustic foam;
• FIG. ⁇ is an illustration depicting that amplitude selective damping is possible with micro-lattice materials because a threshold stress is necessary to trigger buckling and concomitant -energy absorption;
• FIG. 12A is an illustration of a constrained-layer damping setup
• FIG. 128 is an illustration depicting the object to be dampened, as being struck, which causes the .materials to deform and shear in the middle layer.
• the present, invention relates to a micro-lattice and, more particularly, to a micro-lattice damping material and a method for repeatable energy absorption.
• the following description is presented to enable one of ordinary skill in the art to make and use the invention and to incorporate it in the context of particular appl ications.
• Various modifications, as well as a variety of uses in different applications will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to a wide range of embodiments.
• the present invention is not intended to be limited to the embodiments presented, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
• the present invention relates to a micro-lattice and, more particularly, to a micro-lattice damping material and a method for repeatable energy absorption (through reversible deformation).
• a suitable micro-lattice that can be used as a damping material in accordance with the present invention was described in U.S. Non-Provisional Utility Application No. 13/584,108, filed on August 13, 2012, entitled, "Ultralight Micro-Lattices and a Method for Forming the Same", which is incorporated herein by reference as though fully set forth herein.
• the present invention is operable to provide high damping, specifically acoustic, vibration or shock damping, by utilizing the energy absorption mechanism of hollow tube buckling (as provided for by the micro- lattice) ,
• the invention entails a three-dimensional lattice structure of interconnected hollow tubes that has a high damping or loss coefficien
• a unique aspect is the energy absorption by elastic buckling of the hollow tubes and/or nodes where the tubes intersect, which is fundamentally different fiom conventional damping mechanisms and can be used for acoustic, vibration and shock damping.
• the micro-lattice allows for dampening efficacy at a fraction of the weight of other materials.
• this invention enables the design of metallic or ceramic micro- lattice materials with damping properties similar to viscoelastic polymers while retaining the advantages of metals or ceramics, for example temperature insensitivity (compared with only 20-30 Celsius range for viscoelastic materials), environmental stability, high specific stiffness and strength.
• the material can he utilized as an acoustic absorber that is
• Additi nally it can be utilized in, for example, automobiles as a vibration dampener to dampen sound and provide for impact protection, in another aspect, it can be used as a constrained layer damper to dampen vibrations of panels in a plane or rotorcraft fuselage, particularly with lower weight, less temperature dependence and multifunctional properties (e.g., simultaneous vibration damping and heating/cooling), in yet another aspect, it ca be used as a high temperature damper that enables acoustic and vibration damping close to combustion and turbine engines, which are ofte the source. I space applications, it can be used as a dep!oyable vibration or shock damper, utilizing the recoverable deformation ability of the lattice.
• a vibration dampener to dampen sound and provide for impact protection
• it can be used as a constrained layer damper to dampen vibrations of panels in a plane or rotorcraft fuselage, particularly with lower weight, less temperature dependence and multifunctional properties (e.g., simultaneous vibration damping and heating/cool
• the micro-lattice can be employed as a cushion for fragile paySoads during spacecraft launch or, in yet another aspect, it can be used as an acoustic absorber for underwater applications, such as on ships and submarines.
• the unique properties of the micro-lattice allow it to be utilized in a variety of damping applications.
• the present invention is directed to a micro-lattice damping material and the associated damping mechanism.
• the damping mechanism is based on energy absorption by elastic buckling of hol lo tubes as illustrated in FiGs.
• FIG. i A depicts a hollow tube 100 of a damping mechanism, illustrating a force 102 being applied to the hollow tube 100 and demonstrating hollow tube buckling that is reversible and absorbs energy.
• FIG. I B is a chart illustrating energy absorption of the hollow tube 100 as it buckles.
• FIG. 1 A illustrates a single hollow tube 100, as shown m
• FIGs. 2A and 2B it is to be understood that the invention includes a three- dimensional lattice structure of interconnected hollow tubes that form the micro-lattice damping material 200.
• FIGs. 2A and 2B illustrate two examples of the micro-lattice damping material 200.
• the micro-lattice damping material illustrated in FIGs. 2A and 2B can be formed using any suitable technique, a non-limiting example of which was described in U.S. Application No. 13/584,1.08. As noted above, this micro-lattice 200 has a high damping or loss coefficient and can be used for acoustic, vibration and shock damping.
• the damping material can be formed of metallic or ceramic micro- lattice materials (or any other suitable material) with damping properties similar to viseoelastic polymers while retaining the advantages of metals or ceramics, such as temperature insensitivity, environmental stability, high specific stiffness and strength.
• a metallic Ni-7%P micro-lattice damping material has been demonstrated with a loss coefficient tan ⁇ ⁇ 0.2, which is ten times higher than conventional nickel foams.
• Such a material was formed by eleetroless nickel plating a thin coating of Ni-7%P onto polymer micro-lattice templates (as described in U.S. Application No. 13/584,108 and depicted in FIG. 3).
• a non- limiting example of a suitable liquid photomonomer 300 is a thiol-ene resin.
• architectures can be generated with 1 - 4 mm lattice member length L, 100-500 ⁇ lattice member diameter Z), 100 - 500 rim wall thickness t, and 60° inclination angle ⁇ , similar to the micro-lattices depicted in FlGs,
• polymer lattice 306 is an. open cellular
• films e.g., confornial nickel-phosphorous thin films
• the template is coated using any suitable deposition technique, non-limiting examples of which include electroless-platmg 308,
• electrophoretic deposition chemical vapor deposition, physical vapor deposition, atomic layer deposition, solution deposition or sol-gel deposition.
• electrophoretic deposition works well for niulticomponent alloys e.g. steel.
• Chemical vapor deposition and physical vapor deposition work well for diamond and titanium nitride, respectively, while atomic layer deposition, works well for silica.
• the deposition techniques described above can also be employed with ceramic materials as desired. [00079] Thereafter, the polymer is subsequently etched out 3 10 (via chemical etching or any other suitable etching technique that is gentle enough not to destroy the micro-lattice).
• the etchant has to be selective with respeci to the template and the coating material, i.e. , the etching rate of the template needs to be substantially faster than that of die coating.
• the coating material i.e. , the etching rate of the template needs to be substantially faster than that of die coating.
• sodium hydroxide solution is a desired etchant.
• organic solvents, plasma etching, thermal pyrolysis or other etchants are favored. Freeze drying is used for fragile micro-lattices that are deformed by capillary forces on removal from solution.
• the auto-catalytic eiectroless nickel plating reaction enables deposition of thin films with controlled thickness on comple shapes and inside pores without noticeable mass transport limitations.
• micro- lattice material 200 essentially translates the deposited nano-scale thin film in three dimensions to form a macroscopic material where the base structural elements are hollow tubes (as shown in FIG. 1 ).
• any suitable material can be deposited on the polymer lattice 306, non-limiting examples of which include nickel, zinc, chrome, tin, copper, gold silver, platinum, rhodium, aluminum, a ceramic, including, diamond, diamond like carbon, alumina, zirconia, tin oxide, zinc oxide, silicon carbide, silicon nitride, titanium nitride, tantalum nitride, tungsten nitride, a polymer including paxylene or combinations or alloys thereof, including multi-layers of different materials.
• TEM transmission electron microscopy
• FIGs. 4A through 4D provide images of a micro-lattice sample 400 with 14 mg/cc (L: 1050 ⁇ ⁇ ⁇ , D: 150 pm, t: 500 ran) during compression testing while FIG. 5A conveys the corresponding stress-strain curve measured at a prescribed displacement rate of 1 ⁇ sec.
• the sample was not attached to face sheets or the
• FIG. 4A depicts the micro- lattice sample 400 prior to compression.
• FIG. 4B upon first compression, the lattice exhibits a compressive modulus of 529 kPa, with deviations from linear elastic behavior starting at a stress of l OkPa. The stress decreases slightly after the peak associated with buckling and node fracture events, and a broad plateau is subsequently formed in the stress- strain curve as buckling and localized node fracture events spread through the lattice.
• FIG. 4C shows the micro-lattice at 50% compression. Upon unloading, the stress drops rapidly but does not approach zero until the platen is close to its original position.
• FIGs. 4E through 4H provide images of the micro-lattice sample through its compression and recovery. More specifically, FIG. 4E is an optical image of a unit cell of the micro-lattice, in an unloaded or uncompressed condition. FIG. 4F is an optical image of the unit ceil, depicting how the unit cell accommodates compressive strain by buckling at the nodes, FIG. 4G is a scanning electron microscopy (SEM) image of a node before testing, while FIG. 4H is an SEM image of the node after six compression cycles at 50% strain.
• SEM scanning electron microscopy
• the micro-lattice shows significant hysteresis during compression experiments, allowing a measurement of the energy absorption, which is estimated to be 2.2 mi for the first cycle. After three cycles a nearly constant energy loss coefficient of -0.4 is calculated by dividing the absorbed energy by the total energy required for compression (as shown in FIG. SB).
• FIG. 5C shows the stress-strain curves of the first two compression cycles of a sample with a density of ng/cc and larger unit cells (L: 4 mm, D: 500 ⁇ , t; 120 nm) illustrating similar behavior of different micro- lattices in the ultra-low density regime. Increasing the density and wail thickness will eventually lead to compression behavior more typical for metallic cellular materials.
• FIG . 5.D shows the compression of a sample with 43mg/cc (L; 1050 pin, D; I SO pm, t; 1400 nm): notice that strain recovery upon unloading from 50% strain is essentially absent.
• the hollow tubes have a wall thickness and a diameter, such that wall. thickness to diameter ratio is less than 3 y (i.e., 3 multiplied by y), where y denotes the yield strain material property of the material forming the hollow tubes.
• t/D must he on the order of or smaller than 0.01 for reversible deformation (buckling) and high damping, and the yield strain of the Ni-7%P has been determined to be 0.012 by measuring the yield strength as 2500 MPa and the Young' modulus as 21.0 GPa.
• the yield strain is different. In the ease of copper it is 0,0034 and, therefore, the hollow tube aspec t ratio t/D must be on the order of or smaller than 0.0034 to enable reversible deformation and high damping.
• the mechanics of the reversible buckling and how different materials perform was described in further detail by Kevin J. aloney, Christopher S.
• micro-lattices exhibit completely different bulk
• FIG. 6 through 9 illustrate results of dynamic mechanical analysis (DMA) on a sample micro-lattice (such as that illustrated in FIG. 2A). More specifically, FIG. 6 is a graph illustrating the damping coefficient (tan ⁇ ) and strain vs.
• DMA dynamic mechanical analysis
• FIG, 7 is a graph illustrating the damping coefficient vs. strain of a pre- compressed. Ni-7%P micro-lattice with a density 5 12mg/cnv > in a
• FIG. 8 is a graph illustrating the damping coefficient and shear modulus vs. amplitude of a i-7%P micro-lattice with a density
• FIG. 9 is a graph illustrating the damping coefficient vs. frequency of a i-7%P micro-lattice with a density ⁇ 20mg/cm '> in a shear DM A test at two different amplitudes and two different pre-compression strains.
• DMA measured a damping coefficient (tan ⁇ ) of up to 0.22 for nickel micro-lattices (e.g., node-to-node spacing- 1 mm, diameter-] 50 ⁇ ⁇ ⁇ , truss angle ::: 60°, wall thickness ::: 0.3-0.5pm) in compression and shear.
• nickel micro-lattices e.g., node-to-node spacing- 1 mm, diameter-] 50 ⁇ ⁇ ⁇ , truss angle ::: 60°, wall thickness ::: 0.3-0.5pm
• a typical nickel foam with a relative density between 3 and 4% density between 0.24 - 0.32 g/cc
• micro-lattice also allows tor acoustic damping.
• micro-lattice materials are fairly transparent to sound waves due to their large and periodic porosity, they can absorb sound well when it is coupled into the structure with a face sheet. Preloading the micro-lattice by compressing the microlattice structure to strains between 3% and 50% increases the absorption coefficient due to increased damping performance as observed in the DMA tests.
• the damping material can include the micro-lattice and two other materials or layers (such as the object to be dampened and the constraining layer (as shown in
• FIG. 12 or two constraining layers that sandwich the micro-lattice therebetween).
• FIG. 1 1 illustrates the concept of an amplitude sensiti ve damper based on micro-lattices that require a threshold stress to trigger buckling and energy absorption.
• the micro-lattice damping material can. be used to build an acoustic switch or limiier or a vibration damper that only reacts to large vibrations or shocks/impacts while providing high stiffness and strength under normal operating conditions.
• the non-linear elastic behavior of the micro-lattice is used. Under low excitation pressure, the material acts linearly and passes most of the acoustic (or vibration) energy. At higher amplitudes the material begins to damp more significantly and shows larger absorption.
• the micro- lattice damping material enables amplitude specific damping due to the underlying buckling mechanism that requires a threshold stress to occur.
• conventional damping materials react to any amplitude.
• micro-lattice can be used as a damping material in the walls or components of aircraft or submarines that experience variable bias pressure on structures.
• the micro-lattice architecture can be optimized to maximum energy absorption.
• the cellular architecture can also be tuned to design the appropriate buckling strength depending on the application and loading conditions. For example, the compression and shear properties (modulus and strength) are h hl dependent on the lattice member angle. Therefore, for the same material (Ni-P) and density, the lattice member angle can be changed to either increase or decrease the buckling strength. Changing the lattice member angle can be
• FlGs. S.2A and 128 shows a constrained layer damper according to the principles of the present invention that can be applied for use in cars, planes, or any other structure that ca benefit from damping.
• Traditional constrained-layer damping is a mechanical engineering technique for suppression of vibration and typically includes a viscoelastic material that is sandwiched between two sheets of stiff .materials that lack sufficient damping by themselves. Instead of a viscoelastic layer and as shown in FIGs 12A and 2B, the viscoelastic layer is replaced ' with a micro-lattice damping material 1200.
• the micro-lattice damping material 1200 fas compared to viscoelastic materials
• the micro-lattice layer 1200 is sandwiched between the object to be dampened 1202 and a constraining layer 1204.
• the object to be dampened 1.202 is any suitable object that can benefit f om damping, such as the exterior of an automobile, the exosiructure of a plane, etc.
• the object to be dampened 1.202 is any suitable object that can benefit f om damping, such as the exterior of an automobile, the exosiructure of a plane, etc.
• the object to be dampened 1.202 is any suitable object that can benefit f om damping, such as the exterior of an automobile, the exosiructure of a plane, etc.
• the object to be dampened 1.202 is any suitable object that can benefit f om damping, such as the exterior of an automobile, the exosiructure of a plane, etc.
• the object to be dampened 1.202
• constraining layer 1204 is any material or layer (e.g., face sheet) that holds the micro-lattice layer 1200 against the object to be dampened 1202.
• the constraining layer 1204 is a thin sheet of a stiff arid strong material (e.g., plastic, metal, etc.) to force the micro-lattice layer 1200 to deform (i.e., shear).
• a stiff arid strong material e.g., plastic, metal, etc.
• the invention is not intended to be limited to a 'layer" as the micro-lattice can be formed in any suitable shape, such as a block, layer, post, etc.
• the micro-lattice can be attached with or positioned between one or more face sheet (e.g., constraining layers).
• a different architectare than measured in the DMA experiment may be desired for a constrained layer damper, specifically a structure thai undergoes buckling in shear.
• the micro-lattice material can potentially provide several advantages to existing viscoeiastic polymer based treatments. First, damping can be achieved across a broad temperature range including space and cryogenele environments (e.g. , less tha 100 degrees Celsius, etc.) which are currently limited to surface area friction techniques, such as particle damping.
• viscoeiastic materials with high loss factors are typically very soft.
• a mechanical leverage component such as a spacer block; is placed between the panel and the viscoeiastic material.
• T spacer block adds significant volume and mass to the damping treatment.
• Micro-lattice damping materials can be fabricated from metallic materials and exhibit high damping while retainin metallic properties including electric and thermal conductivity, environmental, stability, hig temperature capability (e.g., greater than 300 degrees Celsius), high stillness.
• nickel micro-lattices have demonstrated a loss coefficient (tan For reference, a typical nickel foam with density between 3 and 4% has a loss coefficient of -0,01 -0,02.
• micro- lattice damping As another advantage over the prior art, micro- lattice damping
• materials can be fabricated from ceramic materials (e.g., oxides, S13N4, SiC, diamond) and can be designed to exhibit high damping while also exhibi ting properties of the constituent ceramic, including oxidation resistance, corrosion resistance, ultra-high temperature capability, i ezoe !ectrieity .
• ceramic materials e.g., oxides, S13N4, SiC, diamond
• micro-lattice damping materials can operate in large temperature ranges (e.g. -100 degrees Celsius to 500 Celsius for Ni-7%P 3 or over ranges greater than 200 degrees Celsius, etc. ) in contrast to conventional visco-elastic polymer dampers that are limited to a small temperature range around their glass transition temperature.
• Micro- lattice damping materials offer multifunctional opportunities due to their open cellular structure, for example tor simultaneous damping and active cooling or heating, damping and energ storage, damping and impact blast energy absorption, and others.
• micro-lattice damping materials can be designed to provide anisotropic damping properties. Selecting a unit cell that is not cubic (in the sense of Bravais lattice theory) typically results in anisotropic mechanical properties. For example, a tetragonal unit cell wit a truss angle of 60 degrees (as in one aspect) results in higher stiffness and strength in the longer direction (90 degrees) as compared to the two shorter directions (0 degrees). This anisotropy also affects the damping properties resulting in a higher damping efficiency in the 90 degree direction than in the 0 degree direction. The anisotropy can be increased by changing architectural parameters accordingly, for example, a steeper angle (70 degrees) increases the anisotropy.
• micro-lattice damping materials are ultra light- weight.
• metallic Ni ⁇ 7%P micro-lattices with a density of 0.0J /cm J have been demonstrated with a loss coefficient tan ⁇ - 0.2 while viscoeiastic polymers can achieve loss coefficients close to 1 but have a density around l «/cm ' ⁇ lOOx higher than micro-lattices.

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• 2014
  • 2014-01-15 EP EP14783088.9A patent/EP2946127A4/de not_active Withdrawn
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