Body armor utilizing superelastic spacer fabric, superelastic 3D knits and weaves and/or other superelastic 3D constructs so as to reduce behind armor blunt trauma (BABT)

Abstract

Body armor comprising a projectile-resistant outer layer and an energy-absorbing inner layer, wherein the energy-absorbing inner layer comprises a superelastic three dimensional construct.

Claims

1. A body armor comprising: a projectile-resistant outer layer; and an energy-absorbing inner layer, wherein the energy-absorbing inner layer comprises a superelastic three dimensional construct including a plurality of superelastic fibers that define a first face and a second face of the energy-absorbing inner layer, wherein at least one of the first face and the second face of the energy-absorbing inner layer are superelastic, and voids, which are defined between the plurality of superelastic fibers, wherein the voids are empty spaces, wherein the body armor does not comprise foam.

2. The body armor according to claim 1 wherein the projectile-resistant outer layer comprises ceramic plate.

3. The body armor according to claim 1 wherein the projectile-resistant outer layer comprises a para-aramid synthetic fiber.

4. The body armor according to claim 1 wherein the plurality of superelastic fibers comprise a shape memory alloy.

5. The body armor according to claim 4 wherein the shape memory alloy comprises Nitinol.

6. The body armor according to claim 1 wherein the superelastic fibers comprises a superelastic polymer.

7. The body armor according to claim 1 wherein the plurality of superelastic fibers are combined with at least one selected from the group consisting of aramid fibers, ultra high molecular weight polyethylene (UHWMPE), non-superelastic alloys, carbon fibers, polyester, and a nylon.

8. The body armor according to claim 1 wherein the plurality of superelastic fibers comprise at least one of a knit, a weave and an unordered mass.

9. The body armor according to claim 8 wherein the superelastic three dimensional construct comprises superelastic spacer fabric.

10. The body armor according to claim 8 wherein the superelastic three dimensional construct comprises a 3D weave.

11. The body armor according to claim 10 wherein the 3D weave comprises Warp, Fill, and Z-Filler fibers made of a superelastic material.

12. The body armor according to claim 11 wherein the 3D weave comprises an angle interlock or an orthogonal interlock binding, whereby to provide a plurality of structure options.

13. The body armor according to claim 12 wherein the structure options comprise angle interlock through the thickness (A/T); angle interlock layer to layer (A/L); orthogonal interlock through the thickness (O/T); and orthogonal interlock layer to layer (O/L).

14. The body armor according to claim 1, wherein the first face and the second face of the energy-absorbing inner layer are outer surfaces of the energy-absorbing inner layer.

15. The body armor according to claim 1 wherein each of the plurality of superelastic fibers is a Nitinol wire.

16. The body armor according to claim 1 wherein both the first face and the second face of the energy-absorbing inner layer are superelastic.

17. The body armor according to claim 1 wherein the first face is an outermost layer of the energy-absorbing inner layer and the second face is an innermost layer of the energy-absorbing inner layer.

18. The body armor according to claim 1 wherein the plurality of superelastic fibers, the first face, and the second face are all made of Nitinol.

19. The body armor according to claim 1 wherein the superelastic three dimensional construct has a height between 0.025 inch and 0.750 inch.

20. The body armor according to claim 15 wherein each of the Nitinol wires have a diameter between 0.0005 inch and 0.015 inch.

21. The body armor according to claim 1 wherein the superelastic three dimensional construct includes 5 to 25 stitches per inch.

22. The body armor according to claim 1 wherein, in response to an applied stress, a phase of the plurality of superelastic fibers transforms between an austenitic phase and a martensitic phase.

23. A body armor comprising: a projectile-resistant outer layer; and an energy-absorbing inner layer, wherein the energy-absorbing inner layer comprises a superelastic three dimensional construct including a plurality of superelastic fibers of Nitinol, an innermost surface of Nitinol, an outermost surface of Nitinol, and voids, which are defined between the plurality of superelastic fibers, wherein the voids are empty spaces, wherein the body armor does not comprise foam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein:

(2) FIG. 1 is a schematic view of conventional body armor utilizing a conventional backing material;

(3) FIG. 2 is a schematic view of novel body armor utilizing a novel backing material;

(4) FIG. 3 is a schematic view showing superelastic spacer fabric;

(5) FIG. 4 is a schematic view showing the stress-strain curve of Nitinol and steel;

(6) FIG. 5 is a schematic view showing damping capacity as a function of temperature for selected materials;

(7) FIG. 6 is a schematic view showing storage modulus variation with temperature for selected materials;

(8) FIG. 7 is a schematic view showing superelastic spacer fabric knit into various thicknesses;

(9) FIG. 8 is a schematic view showing superelastic spacer fabric knit to an exemplary height;

(10) FIG. 9 is a schematic view showing various filler patterns for superelastic spacer fabric;

(11) FIGS. 10-12 are schematic views showing various stich densities for superelastic spacer fabric;

(12) FIG. 13 is a schematic view showing an exemplary filler density for superelastic spacer fabric;

(13) FIGS. 14A and 14B are schematic views showing various energy absorption mechanisms for fibers;

(14) FIGS. 15-18 are schematic views showing various types of weaves;

(15) FIG. 19 is a schematic view showing a weaving machine; and

(16) FIGS. 20-22 are schematic views showing various woven structures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(17) The present invention comprises the provision and use of novel body armor utilizing superelastic spacer fabric, superelastic 3D knits and weaves and/or other superelastic 3D constructs so as to reduce Behind Armor Blunt Trauma (BABT). See FIG. 2.

(18) Body Armor Utilizing Superelastic Spacer Fabrics

(19) In accordance with the present invention, there is provided a new and improved body armor which utilizes a three-dimensional (3D) spacer fabric construct made of shape memory material such as Nitinol as a backing material for the body armor to reduce Behind Armor Blunt Trauma (BABT). The body armor does not comprise foam. More particularly, spacer fabrics are breathable, lightweight, permeable, porous and crush-resistant constructs which are manufactured through a traditional warp knitting process so as to create a structure having two separate and unique fabric faces (i.e., a first face or a front face or a top face, and a second face or a back face or a bottom face) which are connected to one another by a plurality of vertical filler (or spacer) fibers. See FIG. 3. In accordance with the present invention, the spacer fabric is formed out of a superelastic material such as Nitinol. The superelastic vertical fibers create the elastic response in the superelastic spacer fabric when the first face (or front face or top face) and the second face (or back face or bottom face) are compressed together, by bending, collapsing and then shape recovering. Thus, the use of a superelastic spacer fabric as a backing material for body armor provides excellent force dissipation when the body armor is impacted by a projectile, whereby to reduce Behind Armor Blunt Trauma (BABT). Voids are defined between the plurality of superelastic fibers. The voids are empty spaces. That is, there is no material in the voids. As shown in FIG. 3, the plurality of superelastic fibers can define the first face and the second face of the energy-absorbing inner layer. At least one of the first face and the second face of the energy-absorbing inner layer can be superelastic. Both the first face and the second face of the energy-absorbing inner layer can be superelastic. The plurality of superelastic fibers can contact both the first face and the second face. Additionally, the first face and the second face of the energy-absorbing inner layer can be outer surfaces of the energy-absorbing inner layer. The first face can be an outermost layer of the energy-absorbing inner layer, and the second face can be an innermost layer of the energy-absorbing inner layer. The superelastic fibers, the first face, and the second face can all be made of Nitinol.

(20) With shape-memory metals, pseudoelasticity, sometimes called superelasticity, is an elastic (reversible) response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a crystal. Pseudoelasticity is from the reversible motion of domain boundaries during the phase transformation, rather than just bond stretching or the introduction of defects in the crystal lattice (thus it is not true superelasticity but rather pseudoelasticity). Even if the domain boundaries do become pinned, they may be reversed through heating. Thus, a pseudoelastic material may return to its previous shape (hence, shape memory) after the removal of even relatively high applied strains. One special case of pseudoelasticity is called the Bain Correspondence which involves the austenite to martensite phase transformation between a face-centered crystal lattice and a body-centered tetragonal crystal structure.

(21) Superelastic alloys belong to the larger family of shape memory alloys. When mechanically loaded, a superelastic alloy deforms, reversibly, up to very high strainsup to 10%by the creation of a stress-induced phase. When the load is removed, the new phase becomes unstable and the material regains its original shape. Unlike shape memory alloys that utilize the temperature-based shape memory effect, in superelasticity no change in temperature is needed for the alloy to recover its initial shape. Superelastic devices typically take advantage of the large, reversible deformation of superelastic materials. Some exemplary superelastic products which use superelastic alloys are antennas, eyeglass frames and biomedical stents.

(22) Among other things, the present invention provides a dynamic construct for cushioning and dissipating energy from a projectile. The dynamic construct comprises a metallic shape memory material having vastly improved fatigue life versus that of polymeric alternatives. Metal and polymeric fatigue is the progressive and localized structural damage which occurs when a material is subjected to cyclic loadings. Metals and polymers differ, however, in that polymers are commonly viscoelastic and show hysteretic elastic effects. This is not true for most metals, because they tend to only exhibit linear elastic behavior. However, the relationship between stress or strain amplitude and fatigue life are asserted for polymers in the same way as for metals. Most polymeric materials exhibit significantly less endurance fatigue levels when compared to structural metals (e.g., steel, stainless steel, titanium, Nitinol, etc.).

(23) It is the polymer's hysteretic elastic effects that make a spacer fabric structure so resilient to compressive set, however, polymers are weak compared to metal. With most engineering materials, load increases with deflection upon loading in a linear way and decreases along the same load-deflection path upon unloading. Shape memory metals (e.g., Nitinol) exhibit a distinctly different behaviora shape memory metal exhibits a hysteretic elastic behavior similar to weak polymers, but with the large strength of metals. For example, polymers such as polyester and nylon have approximately 8-10 ksi tensile strength, while a shape memory metal such as Nitinol can have 120-200 ksi tensile strength.

(24) With Nitinol, and looking now at FIG. 4, upon loading, stress first increases linearly with strain up to approximately 1% strain. After a first yield point, several percent strain can be accumulated with only a small stress increase. The end of this plateau (loading plateau) is reached at about 8% strain. After that, there is another linear increase of stress with strain. Unloading from the end of the plateau region causes the stress to decrease rapidly until a lower plateau (unloading plateau) is reached. Strain is recovered in this region with only a small decrease of stress.

(25) Nitinol exhibits a hysteresis stress stain curve allowing for 8% shape recovery before permanent set, which is unique for metals but common for polymers. The last portion of the deforming strain is finally recovered in a linear fashion again. The unloading stress can be as low as 25% of the loading stress. For comparison, the straight line representing the linear elastic behavior (according to Hook's law) for steel is shown in FIG. 4. Nitinol has a hysteresis stress strain curve similar to that of polymers. However, when the spacer fabric is made of strong Nitinol, the spacer fabric can support heavy loads, eventually deflect under these loads, and cushion the loads so as to recover its original shape when the loads are removed.

(26) In one preferred form of the invention, the Nitinol spacer fabric has enhanced cushion energy (CE), cushion factor (CF) and resistance to dynamic compression compared to polymer spacer fabrics when tested per the cushion testing protocol of SATRA (June, 1992, pages 1-7). Cushion energy is the energy that is required to gradually compress a specimen of a material up to a standard pressure using a tensile-compression testing machine. Cushion factor is a bulk material property, and is assessed using a test specimen greater than sixteen millimeters thick. The pressure on the surface of the test specimen at a predefined loading is multiplied by the volume of the test specimen under no load. This pressure is then divided by the cushion energy of the specimen at the predefined load. Lastly, the resistance to dynamic compression measures changes in dimensions and in cushion energy after a prolonged period of dynamic compression.

(27) And in one particularly preferred form of the invention, the spacer fabric comprises a shape memory material (e.g., Nitinol) that is kink resistant. Unlike wires made from most metals, Nitinol wires exhibit the unique quality of being kink resistant. Nitinol wires can be bent 10 times more than stainless steel wire without suffering permanent deformation. For example, a 0.035 inch Nitinol wire can be wrapped around a 0.50 inch diameter mandrel without taking a set (i.e., without permanently deforming), whereas a stainless steel wire of the same diameter can only be bent around a 5 inch diameter mandrel without being plastically deformed. Kink resistance is an important feature of Nitinol for spacer fabrics when being produced on the double bar knitting machines to produce spacer fabrics. Most metals would not allow for the tight radii bending encountered during knitting without kinking, but Nitinol does. In use, Nitinol spacer fabric structures can be completely compressed (crushed) flat and will return to their original height when the deforming force is removed, without kinking. Other structural metal such as steel, stainless steel and titanium will kink if used for the same applications as Nitinol.

(28) In another preferred form of the invention, the Nitinol spacer fabric has enhanced dampening and cushioning characteristics when compared to other metals (and even when compared to polymers) which are attained by exploiting the shape memory material's unique ability to recover large strains due to a solid-solid phase transformation, and to dissipate energy because of the resulting internal friction. It is known that the high damping capacity of the thermoelastic martensitic phase of Nitinol is related to the hysteretic movement of interfaces in the alloy (martensite variant interfaces and twin boundaries). Also, the damping capacity of Nitinol depends directly on external variables such as heating rate, frequency and oscillation amplitude; and internal variables such as the type of material, grain size, martensite interface density and structural defects. With Nitinol, a high damping capacity and a low storage modulus in the martensitic state is observed. It has been verified that during phase transformation, there is the presence of a peak in damping capacity and an equivalent increase of storage modulus. The storage modulus is represented by the elastic component and is related to a material's stiffness.

(29) Nitinol exhibits excellent damping capacity and energy dissipation characteristics relative to other metals including stainless steel, aluminum and brass. Nitinol damping capacity and low storage modulus is observed when the Nitinol is in its martensitic state. During phase transformation, it is verified by the presence of a peak in damping capacity and an equivalent increase of storage modulus. Dynamic properties of viscoelastic materials have been investigated using commercial Dynamic Mechanical Analyzers (DMA). This technique permits the study of the behavior of materials under dynamic loadings relating molecular structure, processing conditions and geometrical properties with material behavior. By applying a sinusoidal load, a sinusoidal response from a material will be measured. The damping capacity is represented by the tangent of the phase angle (Tan ?) between the two signals. The storage modulus, represented by the elastic component and related to material's stiffness, can be also measured. See FIG. 5, which shows damping capacity as a function of temperature for a variety of materials (including Nitinol), and FIG. 6, which shows storage modulus percentage variation with temperature for the same materials.

(30) Using traditional double bar warp knitting machines, the Nitinol spacer fabric can be manufactured in large sheets (e.g., up to 72 wide, with continuous length) that can be die-, laser- or water-cut into very specific sizes. The Nitinol spacer fabric can also be knit into various thicknesses so as to offer various combinations of stiffness and weight. See FIG. 7, which shows the Nitinol spacer fabric knit into constructs of various thicknesses.

(31) The Nitinol spacer fabric may be manufactured with a wide range of physical properties. Significant Nitinol spacer fabric variables include:

(32) (i) Nitinol Wire Thicknessexamples include wire at 0.0005 to 0.015 diameter thickness;

(33) (ii) Height of Nitinol spacer fabric (per ply)examples include height ranging from 0.025 to 0.750 (see FIG. 8);

(34) (iii) Filler Patternthe Filler Pattern can be in various shapes, e.g., the shape of an X or a Trestle or a C. One preferred Nitinol spacer fabric has an X filler pattern (when looking in the end of the spacer fabric) as shown in FIG. 9. Another preferred Nitinol spacer fabric has a trestle filler pattern as shown in FIG. 9;

(35) (iv) Face Stitch Densityexamples are 5-25 stiches per inch (East to West; referred to as Wales) and 5-25 stitches per inch (North to South; referred to as Courses). See FIGS. 10-12;

(36) (v) Filler Densityby way of example, the filler density may utilize approximately 5-25 stitches per inch, FIG. 13 shows 10 stiches per inch;

(37) (vi) Direction of Plies (layers)for body armor backing material, there are preferably multiple (e.g., up to 10) plies of Nitinol spacer fabric; the direction of these plies (i.e., stacked in one uniform direction or, alternatively, stacked in a criss-crossed pattern, e.g., at 15?, 30?, 45? or even 90? from one layer to the next) can have an effect on the strength, stiffness and energy absorption of the Nitinol spacer fabric.

(38) Experimental testing has shown that Nitinol spacer fabric performs extremely well as backing material for body armor. Specifically, Nitinol spacer fabric is significantly lighter, more energy dissipating and has faster recovery characteristics than currently-used Ultra High Weight Molecular Polyethylene (UHWMP) backing material.

(39) Nitinol spacer fabric can be used as a standalone construct behind the ceramic plates in body armor or it can be used in conjunction with other materials, e.g., Kevlar, UHWMP, gels, etc.

(40) It is also possible to create the superelastic spacer fabric of the present invention utilizing a superelastic material other than Nitinol. Thus, for example, the superelastic spacer fabric may be created using a superelastic polymer.

(41) Body Armor Utilizing 3D Superelastic Woven Structures and/or Other Superelastic 3D Constructs

(42) The present invention also comprises the provision and use of novel body armor utilizing superelastic 3D weaves and/or other superelastic 3D constructs so as to reduce Behind Armor Blunt Trauma (BABT). The body armor can include a projectile-resistant outer layer and an energy-absorbing inner layer. The energy-absorbing inner layer can include a superelastic three dimensional construct including a plurality of superelastic fibers of Nitinol, an innermost surface of Nitinol, an outermost surface of Nitinol, and voids. The voids are defined between the plurality of superelastic fibers. The voids are empty spaces. That is, there is no material in the voids.

(43) Woven fiber mats mitigate projectile energy in different ways. The amount of energy absorbed by fibers is largely dependent upon their strain to failure, as depicted in FIG. 14A. A woven fiber mat is effective at absorbing the impact load by dispersing the energy across a network of fibers, as depicted in FIG. 14B.

(44) A fiber mat with high strength and high elongation to failure is thus expected to absorb energy via plastic deformation and drawing (stretching) of the fibers. Additionally, the strain in a fiber is equated to the impact velocity divided by the sonic velocity of the fiber (Eq. 1).

(45) $\begin{array}{cc}\mathrm{.Math.}=\frac{V}{c}& \mathrm{Equation}1\end{array}$

(46) where, ?strain Vimpact velocity csonic velocity of the fiber

(47) The sonic velocity, in turn, is related to the fiber's elastic modulus, as shown in Eq. 2. A higher elastic modulus results in the impact energy wave traveling farther down the length of the fiber due to a greater sonic velocity, and thus a greater volume of fiber absorbs the projectile energy.

(48) $\begin{array}{cc}c=\sqrt{\frac{E}{?}}& \mathrm{Equation}2\end{array}$

(49) where, Eelastic modulus ?density of the fiber

(50) In another preferred form of the invention, Nitinol (and/or other shape memory materials such as other superelastic alloys, superelastic polymers, etc.) may be woven into a three-dimensional woven structure (i.e., a 3D weave) that provides excellent impact attenuation, resistance to knife penetration, light weight, re-compression, texture (and other) characteristics required for body armor. See FIG. 15, which shows various types of 3D weaves which may be used in forming the backing material for body armor.

(51) High performance fiber materials used in body and/or vehicle armors include S-glass, aramid, high molecular weight polyethylene, etc. Continuous fibers are characterized by denier, which is a measure of the weight, in grams, per 9000 meters (29,530 ft.) of fiber. Thus, when comparing fibers that have the same density, a smaller denier equates to a thinner fiber.

(52) Fibers can be woven together into a number of different configurations, some of which are FIG. 15, to provide varying degrees of performance and flexibility. Fiber structures for armor applications have traditionally been in unidirectional, plain, or basket weave configurations. Unidirectional fiber layers may be rotated 90? with respect to adjacent layers to create a cross-ply fabric. Additional woven structures have been studied for armor applications, such as 3D structures to enhance the multi-hit capability of composites.

(53) 3D fabrics are related in principle to 2D fabrics, but possess a noticeable third dimension of significant depth or thickness created during the 3D weaving process. 3D woven structures are generally comprised of a Warp, Fill, and Z fibers. See FIGS. 16-18.

(54) 3D weaves exhibit many attributes including, but not limited to, design flexibility and versatility; inherent resistance to delamination; improved damage tolerance; ability to tailor composite properties to the application; near net-shape preform capabilities; and reduced lay-up complexity and handling time. See FIG. 19.

(55) The two major classifications or definitions of 3D woven mediums are angle interlock and orthogonal interlock binding. From these definitions four different structures can be formed:

(56) (i) Angle interlock through the thickness (A/T);

(57) (ii) Angle interlock layer to layer (A/L);

(58) (iii) Orthogonal interlock through the thickness (O/T); and

(59) (iv) Orthogonal interlock layer to layer (O/L).

(60) See FIG. 20.

(61) 3D woven structures are highly variable and may be tailored to meet different specifications; different patterns and structures are achieved through different location/direction of the Warp, Fill, and Z fibers. A few different 3D woven structures are shown in FIG. 21.

(62) The density of each layer may be engineered to promote a gradient stiffness through the three-dimensional construct. Various materials may be incorporated into the 3D weave to achieve different characteristics. These materials may include, but are not limited to, other shape memory materials (alloys and polymers); aramid fibers; UHWMPE; non-superelastic alloys; carbon fibers; polyester; and/or nylons.

(63) TABLE-US-00001 TABLE 2 Mechanical Properties of Some Fibers, Including Projections for M5? [4] Strength Failure Strain Modulus Fiber (?) (GPa) (?) (%) (E) (GPa) 600-den. Kevlar KM2 3.40 3.55 82.6 850-den. Kevlar KM2 3.34 3.80 73.7 840-den. Kevlar 129 3.24 3.25 99.1 1,500-den. Kevlar 29 2.90 3.38 74.4 200-den. Kevlar 29 2.97 2.95 91.1 1,000-den. Kevlar 29 2.87 3.25 78.8 1,140-den. Kevlar 49 3.04 1.20 120 Carbon fiber 3.80 1.76 227 E-glass 3.50 4.70 74.0 Nylon 0.91 N/A 9.57 M5 conservative 8.50 2.50 300 M5 goal 9.50 2.50 450 M5 (2001 sample) 3.96 1.40 271

(64) Being able to produce a 3D weave made of shape memory allows (SMAs) such as Nitinol is advantageous because of Nitinol's (NiTi) superelastic characteristics. The amount of energy absorbed by fibers is largely dependent upon their strain to failure. Nitinol has large strain to failure, at 8% strain recovery. A woven fiber made of Nitinol is effective at absorbing the impact load by dispersing the energy across a network of fibers. This woven structure can also be woven with one or more other known aramid fibers or projectile protection type fibers. Nitinol has a high strength and high elongation to failure ratio, thus it is expected to absorb energy via superelastic deformation and drawing (stretching) of the fibers. Nitinol can be woven in the cold worked condition, superelastic condition or the martensitic condition or a combination thereof.

(65) TABLE-US-00002 CW = (Cold Worked) SE = (Super-Elastic) Ingot A.sub.s UTS Elongation UTS Elongation Loading Unloading Active A.sub.f Product (? C.) (psi) (%) (psi) (%) Plateau (psi) Plateau (psi) (? C.) Niti#1 ?35 to ?10 200,000 min >4% 180,000 min >10% >70,000 >20,000 ?10 to ?18 Niti#2 ?45 to ?15 250,000 min >4% 210,000 min >10% >80,000 >35,000 0 to ?18 Niti#3 ?80 200,000 min >5% 180,000 min >10% >100,000 >60,000 ?15 Niti#4 ?10 to ?10 220,000 min >4% 180,000 min >10% >65,000 >15,000 ?14 to ?22 Niti#9 ??35 220,000 min >4% 160,000 min >10% >75,000 >25,000 ?0

(66) Nitinol can be three-dimensionally woven to create a complex structure that can be strong enough to withstand projectiles but elastic enough to absorb the energy to reduce the projectile's speed. See FIG. 22. Alternatively, other superelastic materials (e.g., other superelastic shape memory alloys, superelastic polymers, etc.) may be used to create superelastic 3D weaves or other superelastic 3D constructs for use as backing material in body armor.

Modifications of the Preferred Embodiments

(67) It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.