Two-dimensional response of crushable polyurethane foam to low velocity impact

An experimental and numerical study of the two-dimensional response of crushable foam to low velocity impact is undertaken. Rigid polyurethane foam blocks are subjected to normal impact by gravity-driven impactors of different geometries, at velocities ranging from 2 to 4 m/s. The impactors comprise a rectangular block, a wedge-tipped block and a cylinder. Quantities measured during impact are the impactor deceleration, velocity and displacement, and the energy dissipated. The effects of impact velocity and geometry on the deformation and energy absorbed are studied. A two-dimensional numerical model is proposed to simulate the gross deformation induced in the impact process. It employs a lumped mass approach and is formulated in terms of finite deformation. Appropriate equations of motion, stress–strain relations, failure criteria and failure patterns are developed. Results generated by this model exhibit good correlation with experiments, thus substantiating its validity. The proposed model demonstrates advantages over traditional finite element approaches, in that it accommodates severe deformation and extensive structural failure without the problems of excessive mesh distortion and untenable time step reduction which accompany finite element simulations.