High Strain Rate Failure Behavior of Polycarbonate Plates due to Hypervelocity Impact

Developing a fundamental understanding of how polymers respond during hypervelocity impact (HVI), a high strain rate process, is crucial for the potential use of polymers in HVI protection systems. Here, we present the high-strain-rate impact behavior of commercially available polycarbonates with two different molecular weights, 42 and 21 kg/mol. A powder gun and a two-stage light-gas gun were used to achieve the velocities (v 0 ) of a 4 mm projectile impacting the polycarbonate targets over the range of 400–6,500 m/s. The deformation behavior of the polymer during the impact event was captured using high-speed cameras. The impact caused a variety of responses, ranging from deflection of the projectile to complete perforation for higher v 0, leading to major debris cloud formation. These debris clouds consist of both fluid- and dust-like ejecta. The fluid-like debris cloud indicates the melting of polymer caused by the conversion of kinetic energy to thermal energy and subsequent adiabatic heating. The dust-like response can likely be attributed to the brittle failure behavior of polymers, as the polymer became brittle at a high strain rate. Dynamic mechanical analysis (DMA) and dielectric thermal analysis (DETA) on the polycarbonate samples used here indicate an approximately 40 °C increase of T g with increasing frequency from 1 Hz to 10 6 Hz, and such an increase has likely led to brittle behavior. While the leading-edge velocity of the debris clouds and perforation diameters scale linearly with v 0, we found negligible differences in the HVI response for the two molecular weights of polycarbonate tested here. This study displays the importance of v 0 and thickness contributing to responses of polycarbonates undergoing HVI.