Modelling crimp in woven fabrics subjected to ballistic impact

Woven fabrics are widely used in flexible armour systems for protection against fragments and projectiles from small arms. The woven architecture introduces crimp or undulations in the yarns as they pass alternately over and under orthogonal yarns. An undesirable effect of crimp is excessive deflection in fabric armour during impact. The numerical results of ballistic impact and perforation of woven aramid fabric are presented in this paper. The fabric is modelled as a network of nodal masses connected by one-dimensional viscoelastic elements. The focus of the computational simulation is to compare two different ways of incorporating yarn crimp into the fabric model. Tensile tests on strips of the woven fabric show an initial toe region in the load-deflection curve before the curve asymptotically converges to an approximately straight line beyond a certain strain. The first method of introducing crimp into the fabric model is to include the toe region of the load-deflection curve in the constitutive equation describing the viscoelastic elements. The second method to account for crimp is to physically reflect the woven architecture in the fabric model by arranging the chain of linear elements that define each yarn in a zigzag manner.