Impact response of high density flexible polyurethane foam

The impact response of high density flexible polyurethane-based foam was studied in a series of symmetric (both the impactor and the sample made of the same foam) planar impact experiments, with continuous VISAR monitoring of the velocity of the rear sample surface. The impact velocities in these experiments varied from 43 to 605 m/s providing a sample compression over the 0.36–51-MPa pressure range, with the strain rates changing, respectively, from 4 × 103 to 6 × 105 s−1. The linear shock velocity- particle velocity Hugomiot of the foam, US = US0+su = 14.8 + 1.318u, was determined on the basis of the recorded velocity histories. The rise times of the velocity histories allows one to conclude that under shock compression above 3.2 MPa, the initial structure of the foam is completely crushed and the foam resistance to the propagation of the shock is determined by the void-free foam material. The dynamic tensile (spall) strength of the foam, determined in a separate impact experiment with 1-mm thick foam impactor was found equal to 0.3 MPa. Such unexpectedly low spall strength is possibly the result of substantial damage having taken place in the foam during compression.