Effects of Crimp and Slip on Laminar and Woven Fabrics Subjected To Ballistic Impact.

摘要

In the past decade, there has been growing interest and research on improving the performance of soft body armor materials subjected to high-speed ballistic impact. One “by-product” of the production process for these high strength polymer fibers, which are bundled into yarns, is the existence of undulation or waviness in the yarns, known as crimp. While this has always been treated as undesirable, few comprehensive studies have been done on the true effects of crimp in conjunction with yarn slip in ballistic fabrics. We first develop an in-house Finite-Difference (FD) numerical model to study the post-impact but pre-failure behavior of crimped fabrics made with Dyneema? yarns. While there has been past literature that attempted to numerically model crimp in ballistic fabrics, we note that the results provided little insight regarding the strain profile of individual yarns, the growth and evolution of tension and cone waves, and the yarn de-crimping process. Our first fabric model has laminar geometry with out of- plane zigzag crimp, and we validate our results through comparison with previous analytical models developed by the Cornell Phoenix Group. We present the following findings: (i) the peak strain attained by yarns in the fabric is lowered with increase in crimp, but with small sacrifices in terms of velocity deceleration and out-of-plane projectile displacement, (ii) yarn strain build-up towards its maximum value can vary significantly depending on projectile mass and size dimensions, (iii) tension and cone waves’ velocities and shapes are influenced by various parameters including, the rocking viscosity coefficient, and (iv) allowing for frictional slip between the projectile and the yarns beneath it causes a shock wave effect, which changes the very early response behavior of the fabric post-impact. With our first fabric model, we also ensure that local strain concentrations and other dynamic artifacts resulting from the discretization of the structure are suppressed or smoothed.