Effects of pre-tension and impact angle on penetration resistance of woven fabric

High-strength woven fabrics made of polymeric yarns are widely used because of their low density and high toughness, as well as good resistance to high speed loading, particularly ballistic impact. However, their response to impact is complex, due to the woven architecture and rate-dependent behavior of their constituent yarns. This work aims at understanding the effect of applying pre-tension to a woven fabric subjected to normal and oblique impact. A new experimental setup is designed to facilitate application of pre-tension and prescription of specimen inclination. The fabric performance in terms of its ballistic limit is examined, and the variation of the in-plane force experienced by the fabric during impact is also measured. The fabric response for different pre-tensions and impact angles in terms of the ballistic limit is analyzed. In parallel, a numerical model that includes the geometrical features of woven fabric and incorporates the rate-dependent behavior of the yarns, is established. Results generated by the model correlate well with experiments, and yield useful insights into the mechanisms governing fabric behavior, and how pre-tension and impact obliquity influence them. The findings indicate that the fabric response is determined by four primary factors, all of which are affected differently by pre-tension and impact angle: (i) number of yarns involved in the deformation process (increases with pre-tension); (ii) degree of yarn mobility (reduces with pretension); (iii) yarn strain energy absorption capacity (decreases with pre-tension and impact obliquity); (iv) sliding of the projectile against the fabric (increases with impact angle). These combine such that the ballistic limit increases with pre-tension up to a critical value, after which it drops. In terms of impact obliquity, the ballistic limit increases with impact obliquity; this is because there is greater sliding of the projectile against the fabric as the impact angle increases, which offsets the decrease in strain energy absorption capacity associated with asymmetric deformation for oblique impact. (C) 2017 Published by Elsevier Ltd