Experiment on effects of porosity in the interaction of shock wave and foam

Head-on collision of a planar shock wave with open-cell materials was studied experimentally. Three kinds of polyurethane foam are treated: foam 350x70x70, which is of low porosity (phi approximately equal to 0.76) and high density (rho(c)=290 kg/m(3)); foam 50x50x50, which is of high porosity (phi approximately equal to 0.98) and low density (rho(c)=26 kg/m(3)); and foam 13x13x13, which has the same density and porosity as foam 50x50x50, but has a different internal structure of foam material. Stress-strain curves of foams show high nonlinearity and hysteresis. The maximum stress value behind the foam just in front of the solid end wall, is larger than the reflected shock pressure at the normal solid wall. When a shock wave hits a foam surface, part of the shocked gas penetrates into the foam and interacts with the foam material. Measured stress histories at the foam base of the shock tube show stress which is significantly higher than that due to the pressure behind the reflected shock wave at the solid wall. In the high-density foam 350x70x70, the peak stress is the highest, the mobility of gas in the foam is very low, and its dynamics can be approximated by a single-phase problem. In the foam 50x50x50 and low-density foam 13x13x13, peak stresses are low and the peak value depends on the internal structure of the material. In these cases, the mobility of gas in the foam is high, and the dynamics must be treated as a two-phase problem.