Structure of Deformation Waves in Porous Compressible Materials Under the Influence of Shock Waves

Abstract

Paper describes new experimental results concerning compression waves in porous compressible foams due to loading with shock waves generated in gas. A shock tube of 100 x 100 mm cross-section has been used. In addition to piezoelectric measurements and flow visualization, which were described elsewhere, new techniques for measuring the deformation waves in porous compressible media were developed. The density distribution in the deformation wave is determined, based on photodetection of a reference grating on the side face of the foam with short exposure times. The structure of the deformation wave was found to depend substantially on the permeability of the front face of the foam. In particular, the deformation wave in open-pore polyurethane foam was shown to be transformed into a wave-like isolated compression wave with a rarefaction region between the compression wave and the foam surface. The deformation wave in a foam with the front face covered with a thin mylar film is of a different structure, more like that expected in polyurethane if taken to behave like a pseudogas. The rarefaction region disappeared. The effect of pressure magnitude of the incident shock wave on the deformation wave structure was studied. The dependence of the maximum compression of porous medium on impinging wave intensity was obtained. Pressure distributions on the side wall of the shock tube under the foam were taken. The dependence of pressure distribution on the Mach number of the incident shock wave has been studied.