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

Abstract

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 (v0) 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 v0, 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 Tg with increasing frequency from 1 Hz to 106 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 v0, we found negligible differences in the HVI response for the two molecular weights of polycarbonate tested here. This study displays the importance of v0 and thickness contributing to responses of polycarbonates undergoing HVI.