Key issues in body armour threats, materials and design

Textile body armour has been used since the middle of the twentieth century, but it can trace its roots back to silk fabric, leather and other mrrltilayer systems of antiquity. The response of textile armoirr to balhstic impact is complex and not fully understood. Numerous studies of fabric systems have been published, and understanding has slowly developed based on single fibre tests, meso material models and, recently, relatively complete numerical models of multilayer systems (Tabiei and Nilakantan, 2008). Analytical and empirical models have been developed (Cuniff, 1999 Roylance, 1977) which seek to indicate the key fibre and fabric properties required in armour. However, our understanding of the more subtle effects is still somewhat incomplete, with inter-yam and inter-layer interactions remaining to be fully characterised and with models which are only validated across relatively narrow sets of conditions and materials. 

The impact and captnre of a projectile by mnltilayer textile armour can be snmmarised as follows. Upon impact with the first layer of the armour, the material under the projectile is instantaneously accelerated to the projectile velocity. Above some critical velocity the contact load is such that the yams fail and only a small 

The impact process in effect requires two things from the fabric oryams firstly, they should not break, so they should be strong (or tough) and, secondly, the 

4 The pyramidal deformation of an aramid fabric during the ballistic impact of a 1.1 g fragment simulating projectile. 

A number of other factors emerge as contributory properties of the fabric or armour system. If the yams are loosely woven, there is a greater tendency for projectiles to part the yams and penetrate without fully loading them a process known as windowing. This effect is suppressed if the yams are relatively closely woven often this is described by a cover factor - the ratio of the projected area of the individual yams to the area covered by the yams when woven into fabric. 

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Key issues in body armour threats, materials and design... 

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