Novel Deformation Behaviors in Nanoscale Polymer Systems Via Supersonic Micro-Projectile Impact

The performance of materials under very high strain rate deformation and to very large strains is important for applications such as body armor and protection of spacecraft. The high strain rate performance of polymeric materials is both interesting and challenging because they exhibit very significant strain rate, pressure, and temperature dependent deformation behaviors. In addition, they feature many diverse types of nanoscale morphological features and when confined to thin films or other small scale geometries their characteristics like chain mobility, entanglements, microdomain shape and orientation can strongly influence their mechanical behavior compared to the bulk state. Over the past decade, the laser-induced projectile impact test (LIPIT) has been developed and applied to explore the deformation, failure, and recovery of very small test scale specimens of a variety of materials subjected to extreme deformation rates. LIPIT involves micro-projectiles accelerated at targets by rapid expansion of a elastomer launch membrane by a gas bubble produced by a laser ablation, achieving projectile velocities from 100 – 4000 m/s and strain rates on the order of 10⁶ -10⁸ s^-1. The nanoscale high rate deformation behavior of glassy homopolymers, block copolymers, grafted polymer nanoparticles and nonwoven nanofiber and MWCNT mats will be discussed with reference as to how these miniaturized tests on small samples can be translated to provide insight into macro scale performance.