Oblique Ballistic Impact Simulation of Flexible Body Armors Under Viscous Friction

The projectiles have included RCC and spherical shapes, and viscoelastic interactions and slip between the both the projectiles and the target and between the target layers and fabric yarns have been modeled. Besides exploring new phenomena, these models have been useful for validating previous analytical models where various simplifying assumptions were necessary. Thus far, however, the numerical models have had the limitation (albeit a computational advantage) of assuming a symmetric framework whereby numerical solution of only one quarter of the projectile and target plane was necessary. Consequently, only normal (perpendicular) impact could be studied. To address this limitation, we have turned our attention to modeling projectile impact into the full target plane thus making it possible to treat oblique impact at an arbitrary angle of incidence. This would also make it possible to investigate boundary effects (clamped, free) where projectile impact occurs close to one boundary or near a corner. Making such generalizations has resulted in unanticipated challenges arising from modeling rapid projectile sliding on the target, and thus we have ‘backtracked’ to a simpler early version of the discretization model and begun with angled impact by a right circular cylinder (RCC) on a biaxial, plate-like structure. These challenges have led us to focus initially on scrutinizing features suspected of being possible numerical artifacts in the results, or, establishing through well-understood test cases that the features observed are indeed realistic and not artifacts. The most important findings come from a study varying the angle of projectile incidence as well as the coefficient of viscous sliding friction between the RCC projectile and fibrous target. It is shown that increasing the degree of viscous friction eventually leads to increasing fiber strain with angle of incidence up to some angle were a maximum is achieved. Generally, we find that oblique impact gives rise to important phenomena not captured by impact perpendicular to the target.