Dynamic Response of Layered Functionally Graded Polyurethane Foam with Nonlinear Density Variation

Polyurethane foam is most commonly used for its energy absorbing characteristics. The purpose of this study is to experimentally determine the energy absorbing of density graded foam subjected to dynamic loading. To define the energy absorption, the stress-strain relationship is developed under dynamic uniaxial compression via compressive Split-Pressure Hopkinson Bar apparatus; which is used in conjunction with DIC. SPHB yields the boundary stress where DIC is used to find the inertia stress term. Combining the boundary and inertia stress yields a full stress-strain response of the functionally graded foam material. Theoretically, it has been previously determined that for continuously graded foams with a nonlinearly increasing density has increased energy absorbing ability’s. Our proposed experiments are used to validate the theoretical results and benchmark the ability of functionally graded foam to optimize the energy absorption of polyurethane foam. It has been found that the convex density gradient FGFM has a much higher normalized energy absorption when compared to that of a concave density gradient.