Degradation and failure mechanisms in kevlar armor: a study on ultraviolet exposure and multi-impact loading

This study investigates the ballistic performance of Kevlar soft armor fabrics under multiple impact conditions. Furthermore, the impact of long-term ultraviolet (UV) irradiation on the ballistic properties of a set of Kevlar armor panels was examined. A finite element method (FEM) approach was employed to predict the ballistic performance of both pristine and UV aged multilayer soft armor fabrics. Experimental validation of these simulations was also conducted under identical conditions of NIJ (National institute of justice) standards. Further, a novel methodology was proposed to reconcile the discrepancies between simulations and experiments by accounting for perforations in the vicinity of the impact zone. In addition, the critical distance between successive impacts on the armor panel that influences the performance due to cumulative damage was also determined. From the present simulation study, the residual velocity (vr) for the pristine 12 layered armor fabrics was found to be 310 m/s according to NIJ protocol. On the other hand, 32 and 64 hrs UV exposed soft armors revealed an increase in <i>v</i>_<i>r</i> from 340 m/s to 350 m/s. respectively. These simulation results indicate the degradation of ballistic resistance on UV exposure and corroborate well with the experimental observations. Finally, a detailed analysis of stress distribution profiles originating from the point of impact was conducted to gain deeper insights into the damage mechanism.