Quantifying deformation and energy dissipation of polymeric surfaces under localized impact

The mechanical response of polymeric surfaces to concentrated impact loads is relevant to a range of applications, but cannot be inferred from quasistatic or oscillatory contact loading. Here we propose and demonstrate a set of quantitative metrics that characterizes the ability of polymers to resist impact deformation and dissipate impact energy, as well as the strain rate sensitivity of these materials to contact loading. A model which incorporates nonlinear material behavior is presented and can predict the experimentally observed deformation behavior with high accuracy. The micrometer-scale impact response of several polymers has been investigated in the velocity range of 0.7-1.5 mm/s. Two semi-crystalline polymers - polyethylene (PE) and polypropylene (PP) - characterized above the corresponding glass transition temperature Tg, and four fully amorphous polymers characterized well below Tg- polystyrene (PS), polycarbonate (PC), and low and high molecular weight poly(methyl methacrylate) or PMMA termed commercially as Lucite® (LU) and Plexiglas® (PL) - have been considered. In an inverse application, the model and experimental method provide a tool for extracting the relevant material quantities, including energy dissipation metrics such as the coefficient of restitution e. This approach can be used to determine quantitatively the impact energy absorption of polymer surfaces at elevated temperatures through Tg, as demonstrated for PS and PC over the range of 20-180 °C.