An analytical model for ballistic impact on textile based body armour

Polymer fibres with high tenacity and modulus such as Kevlar® are widely used in personal protection applications. Normally these fibres are manufactured into different fabric structures before being assembled layer by layer to form personal protection panels. This paper reports on an analytical model of ballistic impact of multi-layer woven fabrics developed based on the momentum theory and analytical models of single-yarn ballistic impact proposed by previous researchers. This model incorporates the effect of various intrinsic parameters such as yarn linear density and fabric thread density and the effect of various extrinsic parameters such as the projectile dimension and mass. The model also takes into account the phenomenon of strain gradient among the panel layers and its effects on the tensile strain at the edge of the projectile and the angle between the impact line and the yarn axis. In addition, possible shear failure is also considered by using shear strength together with maximum tensile strain as the failure criteria. It has been found that the results from the analytical modelling agree closely with the experimental results. Further, the analytical modelling also reveals that the model is useful in describing the strain distribution history in the primary yarns in each layer of fabric in the panel. It has been concluded here and in other published work that during the ballistic impact of multi-layer woven fabrics shear failure occurs before tensile failure for the front layers which prevents the high strength polymer fibres reaching their full energy absorption potential.