Large-displacement Lightweight Armor

Abstract

Large-displacement Lightweight ArmorRandomly entangled fibers forming loosely bound nonwoven structures are evaluated for use in lightweight armor applications. These materials sacrifice volumetric efficiency in order to realize a reduction in mass versus traditional armor materials, while maintaining equivalent ballistic performance. The primary material characterized, polyester fiberfill, is shown to have improved ballistic performance over control samples of monolithic polyester as well as 1095 steel sheets.The response of fiberfill is investigated at a variety of strain rates, from quasistatic to ballistic, under compression, tension, and shear deformation to elucidate mechanisms at work during ballistic defeat. Fiberfill's primary mechanisms during loading are fiber reorientation, fiber unfurling, and frictional sliding. Frictional sliding, coupled with high macroscopic strain to failure, is thought to be the source of the high specific ballistic performance in fiberfill materials.The proposed armor is tested for penetration resistance against spherical and cylindrical 7.62 mm projectiles fired from a gas gun. A constitutive model incorporating the relevant deformation mechanisms of texture evolution and progressive damage is developed and implemented in Abaqus explicit in order to expedite further research on ballistic nonwoven fabrics.v

Study of dynamic compressive responses of ultra‐high molecular weight polyethylene felt impregnated with shear thickening fluid

“…The photographic images of neat and STF impregnated felt before and after impact is shown in Figure 12. It is observed that for neat felt, the entire longitudinal stress wave generated by the projectile impact passes through the felt and gets reflected at its junction points on account of lossy, frictional, and stick–slip mechanism 16 . This wave induces fiber slippage and ultimately felt gets dispersed at a higher strain rate 41 .…”

“…It is observed that for neat felt, the entire longitudinal stress wave generated by the projectile impact passes through the felt and gets reflected at its junction points on account of lossy, frictional, and stick-slip mechanism. 16 This wave induces fiber slippage and ultimately felt gets dispersed at a higher strain rate. 41 However, less yarn slippage is observed in STF impregnated felt.…”

“…These mechanisms are severely affected by the surface properties of the fiber and the degree of fiber curtailment within the felt. [12,16] It was reported that 17-grain fragments simulating projectile traveling at 450 m/s could be stopped using Dyneema ® Fraglight ® of 1.2 kg/m 2 areal density. [17] While exploring literature, it was found that only a limited study is available on the ballistic application of UHMWPE felt.…”

Empirical Ballistic Limit Velocity Model for Bi-Layer Ceramic–Metal Armor

“…where Proposing empirical forms in eqn (5) for bulk deformation energies: E 1 = σ HEL1 ε 1 in which σ HEL1 is Hugoniot elastic limit (HEL) strength of ceramic plate, ε 1 is compressive failure strain of ceramic, E 2 = σ 2 ε 2 in which σ 2 is the ultimate tensile strength (UTS) of metallic plate, ε 2 is tensile failure strain of metallic plate and considering volumes of ceramic front and metallic backing plugs as:V 1 = πh 1 (ξ 1 R P ) 2 and V 2 = πh 2 (ξ 2 R P ) 2 , respectively, results in an expression for v bl given by: (6) In the next section, material model constants for three ceramic and three metal materials used in numerical simulations, are presented.…”

“…Plugging can result either due to high shear stresses formed around the moving plug directly in front of the projectile or, in the case of ceramics, due to cone cracking. In the limit as projectile velocities increase, shear plugging often becomes the dominant failure mode [6]. High velocity shear plugging occurs when a material has insufficient time to respond to an impact; sufficient stresses, which can cause failure in the armor, build up almost instantaneously at the impact site, with little stress wave propagation occurring prior to complete perforation of the armor, and a plug with approximately the same area as the projectiles frontal area is knocked out of the armor.…”