PC-based numerical modeling of ballistic impact into multi-layered nonwoven fibrous targets

A numerical code has been developed to model ballistic impact into a multilayered, nonwoven composite thin plate. The target consists of N unidirectional layers that are arranged in an alternating, cross-plied configuration. The projectile is either a hard sphere or a right circular cylinder (RCC). Motivation for such a model is the commercial development of soft and plate-like body armor whose building blocks are thin, nonwoven ultrahigh molecular weight (UHMWPE) fibrous sheets consisting of four bonded unidirectional layers with alternating (0o/90o/0o/90o) orientations. The matrix is typically a very flexible polyurethane just sufficient to fill the voids between the fibers, so about 17 percent by mass. Our interest is in modeling various features seen in ballistic impact into such structures. The code, which was written in MATLAB and runs on a PC, involves a forward, finite-difference (FD) scheme of numerical solution. Layers are sub-divided into multiple elastic 'yarn' elements with distributed masses. Elastic and viscous compression (normal) and shear (transverse) elements are used to model inter-layer yarn couplings. Sliding on the projectile follows a viscous friction law. Following impact, the evolution of tension and transverse waves in the layers are modeled, as well as projectile deceleration. Graphical results are presented for velocities, displacements, forces and strains versus time, which we interpret.