Projectile impact on fabric-metal assemblies – Influence of fabric-metal sequence

Abstract

Fabrics woven from high-strength fibres are increasingly employed for protection against projectile impact, because of superior mechanical properties. In some applications, high-strength fabrics are combined with metallic components to provide sufficient structural rigidity and strength – e.g. for vehicle bodies, turbine engine fragment barriers, building doors, etc. An understanding of how the fabric-metal layer sequence affects the resulting ballistic resistance, is essential for effective design of such fabric-metal assemblies. This motivates the current study, whereby multiple plies (1, 2 or 4) of Twaron (T) aramid fabric were combined with an aluminium alloy (A) thin plate to form a lightweight protective panel. The projectile impact penetration resistance of three types of fabric-metal arrangements were examined – i) the aluminium alloy plate as the impact face; ii) the Twaron fabric as the impacted layer; iii) the aluminium alloy plate sandwiched between fabric layers. For assemblies with a smaller number of fabric plies (i.e. 1 or 2), siting the aluminium alloy plate as the rearmost layer results in a significantly higher impact energy absorption capacity, compared to having the aluminium alloy plate as the impact face – e.g. for (A+1T) assemblies, i.e. Al plate+1 ply of Twaron, 1T/A (impact face layer appears first in this nomenclature) performs much better than A/1T. For (A+2T) assemblies, 2T/A provides the highest impact resistance, A/2T is the weakest, and 1T/A/1T lies in between. However, when the number of fabric plies is increased to 4, a variety of responses was observed. An A/4T configuration absorbs significantly higher energy than a 4T/A arrangement, while a symmetrical 2T/A/2T sequence absorbs less energy than either an A/4T or 4T/A configuration. High-speed optical photography images and post-test specimens were analysed, to examine the deformation and failure modes of the fabric plies and Al plate in the fabric-metal targets, and how they are affected by the fabric-metal sequence. These help identify the interaction between the fabric plies and Al plate for various fabric-metal sequences, in order to account for the phenomena observed in experiments.