Deformation Morphologies of Polymeric Materials at Extreme Rates

Polymeric materials present a wide range of mechanical behaviors due to the huge set of types of polymers and their corresponding diverse nano- and micro-scale structures along with their inherent strong sensitivity to deformation rate and temperature. Moreover, due to their ability to experience very large strains as well as in certain situations, to recover and heal, polymeric materials are drawing increasing attention for ballistic applications. This presentation will highlite the deformation behavior in recent laser induced projectile impact testing (LIPIT) of glassy homopolymers, glassy polymer grafted nanoparticles, glassy-rubbery block copolymers, glassy-swollen gel block copolymers, miscible polymer blends and polymer networks based on dynamic covalent bonds. Micron scale hard projectiles are impacted into thick polymers films as well as perforated through thin film specimens. Additionally, microsphere polymer specimens can be used as projectiles to impact against rigid substrates. Incident velocities vary from 100 m/s to 1000 m/s creating extreme strain rates from 10⁶ to 10⁸ s^-1. Samples undergo adiabatic shock compression, shear and equi-biaxial tension, then partially recover as the projectile is either arrested, rebounds or perforates the specimen. Deformation mechanisms are investigated using laser scanning confocal microscopy, transmission electron microscopy and focused ion beam cross sectional scanning electron microscopy. Variations of the incident velocity and film thickness allow insight into the progression of the deformation event. Deformation features such as shear bands, crazes, viscoplastically drawn fibrils and circumferential fractures.