| Polycarbonate is widely used for protective eyewear due to its exceptional optical and mechanical properties, but there has been limited application of finite element analysis to predict its impact behavior. The objective of this research is to compare experimental and numerical results of the normal impact of steel projectiles into circular, thin-walled, injection molded lenses, rigidly fixed about their perimeter. This constitutes an investigation into a state-variable constitutive model to characterize the nonlinear strain-rate-sensitive material behavior of polycarbonate, and to apply it through dynamic finite element analysis. A new modified Ramaswamy-Stouffer state-variable model is developed for ductile plastics. The original model considers kinematic hardening, and components are added to model a stress overshoot at yield, isotropic hardening and failure. The finite element analyses are accomplished using a user-defined material model implemented in LS-DYNA. |
