Size scale-dependent failure of poly(methyl methacrylate) due to projectile impacts

Polymer glasses, such as poly(methyl methacrylate) (PMMA), are often used in impact mitigation applications where impact-resistance, optical transparency and light-weighting are required. However, our understanding regarding the failure behavior of these materials subjected to high-velocity projectile impact from the nanoscale up to macroscale is limited. In this contribution, we study the projectile impact performance of PMMA using two different projectile impact tests. For nanoscale studies, laser-induced projectile impact testing (LIPIT) was employed to investigate the impact performance of thin PMMA films, on the order of a few hundred nanometers in thickness, at strain rates of ~10⁵ to 10⁷ 1/s. For macroscale studies, PMMA sheets with thicknesses on the order to 10 mm were subjected to ballistic and hypervelocity impacts in the strain-rate regime of ~10⁶ 1/s. By relating the minimum perforation velocity, defined as the minimum impact velocity a material can withstand without catastrophic failure, to specimen geometry and projectile size at these two distinct sizes, we demonstrate how the size-scale of the materials system defines the mechanisms of failure and its impact resistance.