Designing polymer metamaterial for protective armor: a coarse-grained formulation

Abstract

Designing protective armors is important for varied civil and defense applications. Ceramic-polymer composite armors are particularly interesting for their high strength and light weight with high energy absorption capability. While the function of ceramic is to retard ballistic impact penetration, polymer panel serves the purpose of absorbing high energy generating from the propagating elastic/stress waves. Enhancing this energy absorption capability of the armor is essential for its back face signature. Our present study shows that the energy absorption can be considerably enhanced if the bulk polymer panel is replaced with a polymer based metamaterial. To demonstrate this, a comparison of the polymer metamaterial is made with its solid counterpart, i.e., bulk polymer matrix in terms of their respective transmission losses in the propagating elastic waves. We have also studied the effect of size of the polymer metamaterial, e.g., by increasing the number of metamaterial layers and variation in the the fiber length and thickness within a layer. A major challenge in such studies is the extreme computational overhead involved in solving continuum mechanics equations using finite element methods on the complex geometry with microstructure details. Note that microstructure details, i.e., geometry, size and shape are mostly responsible for the nonintuitive properties of metamaterials. We have bypassed the huge computational requirement by proposing a novel coarse-grained methodology based on energetics of the structure for the polymer metamaterial. We envisage that the methodology would be useful to other related studies on mechanical metamaterials. © 2020, Springer Nature B.V.