Effects of layer stacking order on the V₅₀velocity of a two-layered hybrid armor system

Abstract

We develop a theoretical and computational model to investigate the ballistic response of a hybrid twolayered flexible armor system. In particular, we study the effects of stacking order of the two fibrous layers, which have distinctly different mechanical properties, on the V 50 limit velocity. A system consisting of Kevlar and Spectra fabrics is studied in detail. For this system, previous experimental results of Cunniff show nearly a factor of two difference in the V 50 velocities for the two possible stacking orders. The new model presented here extends our previous multilayer model by directly addressing interference effects between the two layers, treated here using length and tension compatibility along the radial direction away from the projectile. The primary task is to calculate strains in the individual layers in the presence of constraining interference that forces the nested layers to have a common impact cone shape different from what would be generated by the impact if the layers were allowed to deform freely. We show that this interference, together with relative areal densities of the layers, have a significant effect on the strain evolution in the layers, particularly near the edge of the projectile where failure initiates. As observed experimentally by Cunniff, our model predicts a large decrease in the V 50 velocity of the hybrid armor system when Spectra is the strike layer. However, to achieve this reduction it is necessary to use a lowered normalization velocity in multilayered Spectra systems than the theoretical value obtained from basic fiber properties. Besides matching the experimental results of Cunniff, the model reveals many subtle transitions in the onset and effects of interference between the layers. Somewhat surprising and contrary to conventional wisdom is the observation that layer interference can sometimes be beneficial depending on the relative mechanical properties and areal densities of the two layers.

Modeling and Experiments on Ballistic Impact into UHMWPE Yarns Using Flat and Saddle-Nosed Projectiles

“…Consequently, fibers underneath are simply in the way, in some respects acting as added mass to the fibers above, thus slowing down the transverse and tensile waves. Interference effects have been demonstrated experimentally by Cunniff [48] and theoretically by Porwal and Phoenix [45] and by Phoenix et al [46], to result in a substantial reduction in the critical failure velocity of multi-layer, hybrid systems. Much the same phenomenon can be expected in yarns.…”

“…with respect to the pulley center, as is discussed in Porwal and Phoenix [45] and Phoenix et al [46]. (This velocity reflects the fact that the center of the pulley is moving at velocity c i with respect to ground, whereas the material is moving at velocityu (+) i with respect to ground, so the second must be subtracted from the first to obtain the relative speed at which material passes over the pulley.)…”

Investigation on energy absorption efficiency of each layer in ballistic armour panel for applications in hybrid design

“…This leads to reduction of energy absorption in a panel when a material with high modulus was placed before a material with low modulus. Above test results have been investigated by Porwal and Phoenix [18] through a theoretical and numerical model. It was found that the interference between two layers had a significant influence on strain evolution in layers, in particularly near the edge of the projectile where failure initiates.…”

Yüksek Performanslı Kumaş Zırhların Balistik Dayanımlarının Sayısal Olarak İncelenmesi

“…Son yıllarda, Phoenix ve ekibi tarafından [16][17][18] gerçekleştirilen analitik çalışmada düz uçlu bir çarpanın 2-boyutlu membrana çarpmasını incelenerek, membranın balistik cevabı elde edilmiştir.…”