Filament-level modeling of Kevlar KM2 yarns for ballistic impact studies

For the past decade, numerical ballistic fabric impact research has centered on homogenized yarn based models. However there has been an increasing emphasis in recent years to study the behavior of woven aramid fabrics at the filament scale to investigate the various deformation and energy dissipating mechanisms at the micron length scale. Such an investigation cannot be accomplished through experimental testing. A large gap still exists between the filament-to-yarn length scales. In this study single yarn transverse impact tests of a Kevlar KM2 yarn are simulated using a finite element analysis. All of the 400 filaments in the yarn are explicitly modeled using 3D solid elements and assigned experimentally characterized material properties. The effects of projectile-yarn and inter-filament friction, and filament material properties on the impact response are studied by considering two scenarios where the filaments are either constrained from spreading laterally during the impact event or are left unconstrained. The packing pattern, filament redistribution, and filament energies are monitored during the impact event. The high degree of model resolution provides invaluable insight into the impact behavior of the ballistic yarn and demonstrates the sensitivity of the impact response to filament friction, material properties, and spreading and redistribution.