The specific energy absorption (Ep*) by a protective shield during projectile impacts depends on many factors, including material’s constitutive response, density, and layer thickness, deformation and failure mechanisms, and projectile’s shape, mass, and velocity. Laser-induced projectile impact test (LIPIT) allows testing sub-micron-thick materials with individual microparticles selectively launched at controlled velocities, offering an efficient high-through-put and cost-effective alternative to conventional ballistic testing. Small test sample volumes and the ability to perform holistic deformation analysis of the entire impact zone down to the atomistic scales make LIPIT attractive to study emerging materials as well as enable computational modeling at scale. Prior studies on emerging materials tested with LIPIT reported exceptionally high Ep* compared to the bulk materials tested at the macro-scale. This enhancement has been attributed to the potential material evolutions and nanoscale size effects. However, the geometric scale differences from macro to LIPIT experiments can cause significant strain rate changes, and their effect is not well understood. To elucidate these mechanisms, we designed a matrix of LIPIT experiments where polystyrene sheets of varied thickness t, impacted with silica projectiles of varied diameter D at impact velocities varying between 200 and 800 m/s. Our results show a direct correlation between D/t and Ep*, where higher specific energy absorption is seen at larger D/t. We further observe a geometric scale dependency for Ep*, where smaller scales exhibit higher Ep* at the same D/t. Using a scaling analysis, we reveal the existence of a master ballistic curve for Ep*, accounting for the geometric dependency. Our results demonstrate that the geometric effects must be accounted for before comparing the ballistic performance of different materials across different test scales.
2025-04-09 09:00:00
