Reverse engineering for estimation of shear modulus for yarn models in finite element modelling for ballistic impact

Abstract

In finite element (FE) modelling of ballistic performance of fabric, shear moduli of continuous yarn models are usually specified based on approximations and assumptions, despite their significant influence on energy absorption and yarn failure time in a ballistic impact event. This paper applies reverse engineering method for estimating shear modulus G13 of a continuous multifilament yarn model for simulating the ballistic behaviour of the yarn or its fabric. A ballistic event of Dyneema® SK65 yarn model impacted by a projectile travelling at 477 m/s is used to illustrate the establishment of the methodology. The procedure starts by relating G13 and transverse wave velocity (ut) through regression whose correlation factor R2 is 0.999. ut is calculated by the classical Smith equations. The regressed relation and the availability of ut value enable the calculation of G13. The simulated results of the Dyneema® yarn model with such estimated G13 show healthy agreements to the analytical and experimental counterparts in terms of ut and the slope angle of fabric deflection θ. The reverse engineering method has been used for obtaining G13 successfully for yarn models of other materials, e.g. Kevlar KM2 and Zylon®, in simulating their transverse deflection behaviour under the ballistic impact.