The nature of polymer deformation depends on the ability of the chain segments to respond to the applied load at the imposed loading rate. When the polymer response time is significantly longer than the loading duration, the polymer responds in a brittle manner. Polystyrene, for example, is a brittle, glassy solid at room temperature and absorbs very little energy during deformation. Here we show unexpected, thickness and strain-rate-dependent deformation processes in thin polystyrene films at extreme axisymmetric tensile deformation rates. The impact of a supersonic micro-projectile initiates crazing, yielding, and adiabatic heating leading to extensive plastic flow of a load-bearing viscoelastic melt prior to perforation and film rupture. The less entangled, more mobile near-surface regions of these freestanding films favorably modify these processes, increasing the specific energy absorption as thickness decreases at the highest impact velocity. This results in unprecedented energy absorption at extreme strain rates in what is normally considered a brittle material.

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DOI: 10.1016/j.mattod.2018.07.014