An experimental study of high-velocity impact on elastic–plastic crushable polyurethane foams

The mechanical behavior of elastic–plastic polyurethane foams was studied experimentally under high-velocity local impact loading in normal and oblique directions, in particular, the energy absorption and the situation of damage zone were investigated. In order to obtain the mechanical properties, at first quasi-static compressive global loading was performed on the foams. Then, several samples of rigid polyurethane with different thicknesses (between 10 and 80 mm) and densities (between 40 and 320 kg/m3) were prepared and subjected to high-velocity normal impact loading (with projectile velocity range between 30 and 140 m/s). The results showed that the foam with density of 320 (kg/m3)320 (kg/m3) at thickness of 40 (mm) has the highest energy absorption between them and also increasing the density and thickness of the foam increases the energy absorption and the area of the damage zone on rear side of the foam. Furthermore, it was found that the damage area consists of two different cylindrical and frustum-like zones. It was shown that the absorbed energy was dependent on both density and thickness; therefore, it was attempted to statistically formulize the relationship between absorbed energy on the one hand and thickness and density on the other hand based on experimental data. The effect of projectile nose including the five shapes such as flat-ended, hemi-spherical, semi-elliptical, right-conical and sharp-conical was investigated on penetration depth of projectile into the target. The results have revealed that the penetration depth increases with decreasing in the curvature radius of projectile nose cross-section; hence, the foams were too weak against sharp noses. On the other hand, performing the oblique impacts showed that increasing the oblique angle increases the damage area and changes the shape of rear side from ellipsoid-like to triangle-shape.