On the dynamic response of polymeric foams

This study examined the mechanical response of four polymeric foams under quasi-static and dynamic loading conditions to explore the protective impact mitigation applications of polymeric cellular materials. Polyethylene, polyurethane, and polystyrene, all with relative densities between 1.5-3%, and a bilayer polymeric foam with a trademarked name Zorbium were the four foams analyzed. With the extensive use of image analysis techniques (digital image correlation), the quasi-static local strain behavior of these cellular materials was determined. The dynamic impacts, using a gas gun apparatus and high-speed camera imaging in direct impact experiments, were evaluated to study the dynamic shock response. The experiments generally show a much greater dynamic stress response for the foams compared to their quasi-static responses and suggest a significant difference from the slow rate compressive response. Higher impact velocities resulted in shock formation and propagation. Using conservation of momentum and Rankine-Hugoniot jump conditions, the stresses in the foams were determined. The Shock-Hugoniot of impact velocity and shock wave speed was generated from the experimental results to characterize the high-speed dynamic response of the four foams. The two-layer composite foam, with differing stiffnesses and similar pore sizes, in slow and fast impact experiments, is discussed and analyzed using similar methods used for polyethylene, polyurethane, and polystyrene foams. Finally, the impact problem is examined numerically using the method of characteristics; the results of these simulations are used to determine the force transmission characteristics of protective foam layers. This method is shown to be an effective tool for design