Constitutive modeling of energy-absorbing foams using LS-DYNA

Low-density polyurethane foams have been widely used in automotive energy absorbing systems, e.g. bumpers, knee bolsters and instrument panels. A reliable and robust constitutive material model is necessary for analyzing potential designs of these energy management systems. The three-dimensional compressive-stress strain response of polyurethane foams under compressive impact loading has been studied. The material parameters are derived from a range a compressive tests where strain rate, temperature and density are varied. The constitutive model is implemented into LS-DYNA using the *MAT_USER_DEFINED_MATERIAL_MODEL option, and the Levenberg-Marquardt method is used to solve the highly coupled constitutive equations for the six normal and shear stresses. The capabilities of the material model are demonstrated for high-speed impact analyses of potential designs.