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

An experimental and numerical study of the two-dimensional response of crus hable foam to low velocity impact is undertaken. Rigid polyurethane foam bl ocks are subjected to normal impact by gravity-driven impactors of differen t geometries, at velocities ranging from 2 to 4 m/s. The impactors comprise a rectangular block, a wedge-tipped block and a cylinder. Quantities measu red 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 numerica l 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 f inite 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 f inite element approaches, in that it accommodates severe deformation and ex tensive structural failure without the problems of excessive mesh distortio n and untenable time step reduction which accompany finite element simulati ons. (C) 2000 Elsevier Science Ltd. All rights reserved.