The interactions of simultaneous Multiple Impacts: A Finite Element Approach

While single ballistic impact problems have been analysed thoroughly, the problem of near simultaneous multiple impacts hasn't received the same attention. Such a condition may be encountered in cases of heavy machine gun fire or fragment cluster impacts that usually are generated from the fragmentation of a case containing high explosives. In this article the interactions between three simultaneous impacts in different configurations, are modelled using Finite Element Methods (FEM) utilising LS-Dyna® package and the results are presented and discussed. An attempt to identify and distinguish the influences of cumulative damage mechanisms and dynamic interactions is presented. Also graphs of residual velocity vs initial velocity for Single and Triple impact simulations are illustrated and commented. To realise these simulations, a typical aramid fabric is modelled using a homogenised orthotropic elastic shell plate to exhibit the stress wave propagating patterns and three FSP 1.102g simple elastic solids are chosen as projectiles. Different configurations of projectile formations with respect to the material's axes of elastic symmetry are modelled in order to acquire a more thorough understanding of the variations in the impact interactions that may be encountered in real triple ballistic tests. What is more, the effect of radial dispersion of the projectiles is examined. The simulations indicate that the ballistic performance of the aramid fabric is significantly lower under triple impact events. Τhe interactions of impact disturbances superimpose resulting in elevated stress-strain energy density.