G. Mazor

Shock wave interaction with cellular materials

The equations governing the head-on collision of a planar shock wave with a cellular material and a numerical scheme for solving the set of the governing equations were outlined. In addition, the condition for the transmitted compression waves to transform into a shock wave, inside the cellular material was introduced. It was proved analytically that a cellular material cannot be used as a means of reducing the pressure load acting on the end-wall of the shock tube. In subsequent papers, the interaction of planar shock waves with specific cellular materials, e.g., foams and honeycombs will be described in detail.

Shock wave interaction with cellular materials: Part II: open cell foams; experimental and numerical results

In the Part I of this study, namely the analytical part in Mazor et al. (1992), the governing equations of the phenomenon in which a planar shock wave collides head-on with a cellular material and interacts with it were developed using a Lagrangian approach. In addition, the numerical approach adopted by us during the numerical course of this study was briefly outlined there. The present part reports on experimental and numerical results of the head-on reflection of a planar shock wave with an open cell polyurethane foam. Foams as mentioned by Gibson and Ashby (1988) and summerized in Part I of this study by Mazor et al. (1992), are one of the two general types of cellular materials.

Shock waves in saturated thermoelastic porous media

The objective of this paper is to develop and present the macroscopic motion equations for the fluid and the solid matrix, in the case of a saturated porous medium, in the form of coupled, nonlinear wave equations for the fluid and solid velocities. The nonlinearity in the equations enables the generation of shock waves. The complete set of equations required for determining phase velocities in the case of a thermoelastic solid matrix, includes also the energy balance equation for the porous medium as a whole, as well as mass balance equations for the two phase. In the special case of a rigid solid matrix, the wave after an abrupt change in pressure propagates only through the fluid.

Influence of surface roughness on the transition from regular to Mach reflection in pseudo-steady flows

The effect of surface roughness on the transition form regualr (RR) to Mach reflection (MR) over straight wedges in pseudo-steady flows was investigated both experimentally and analytically. A model for predicting the RR \rightleftarrows

Displacement waves in saturated thermoelastic porous media. I. basic equations

MR transition in the ( M i , θ w )-plane was developed ( M i is the incident shock wave Mach number and θ w is the reflecting wedge angle). Its valdity was checked agnainst experimental results. Since the experimental results are limited to the ranges 1 M i \rightleftarrows

Head-on collision of normal shock waves with a rubber-supported wall

MR transition is related to the boundary - layer thickness which in turn depneds on the surface roughness.

Well tailored compressive stress-strain relations for elastomeric foams in uni-axial stress compression

A complete set of macroscopic equations, the solution of which describes fluid and solid stresses, displacements and temperatures, evolving from an excitation of a saturated porous medium domain in the form of an abrupt pressure and temperature changes applied at the domains boundary is presented. The fluid is a compressible Newtonian one and the solid is thermoelastic. Nonisothermal conditions prevail. The set of equations includes mass, momentum and energy balance equations, constitutive relations and definitions. A simple example indicates that the fluid and solid displacements are described by two coupled wave equations.

Stress-strain relations for elastomeric foams in uni-, bi- and tri-axial compression modes

The head-on collision between a normal shock wave, propagating into a quiescent gas, and a rubber-supported plate was investigated theoretically and experimentally. In the theoretical part, a physical model was developed for describing the collision process. Three different modes in which the rubber could be loaded, due to its collision with the incident shock wave, were studied. They are: uni-axial stress loading, bi-axial stress loading and uni-axial strain loading. In the first two modes the rubber can expand while carrying the shock-wave induced compressive load, and therefore can be treated as an incompressible medium. This is not the case in a uni-axial strain loading where the rubber cannot expand while carrying the shock-wave-induced load. The model developed was based on both the conservation equations and on an appropriate strain stress relation which describes the rubber behaviour under loading. The model was solved numerically for each of the above-mentioned loading modes. Experiments were conducted in a shock tube; the rubber response to its collision with normal shock wave was studied for the case of bi-axial stress loading. Pressures, in the gas, and stresses, in the rubber, were recorded by using piezoelectric pressure transducers; the shock-wave reflection, in the gas, and the rubber displacement and compression processes were recorded on successive shadowgraphs. Good agreement was found between the experimental and numerical results for the case of bi-axial stress loading. This agreement validates the model developed for the collision process and the reliability of the numerical scheme used for its solution.

The enhancement of shock wave loads by means of porous media

Well tailored compressive stress-strain relations for elastomeric open and closed cell foams under a uni-axial stress compression were developed. These sets are aimed at replacing those presented by Gibson and Ashby (1988) [1] since they are mismatched and cannot be used. The proposed set of compressible stress-strain relations for elastomeric open cell foams was compared with experimental results. Good agreement was seen.

Head-on Collision of Shock Waves with Porous Materials: Experimental and Numerical Investigation

SummaryBased on suggestions given in [1], the uni-axial compressive stress-strain relations for elastomeric foams, which were developed in [2], have been extended to cover the bi- and tri-axial stress modes of compression for both open- and closed-cell elastomeric foams.The stress-strain relations for uni- and tri-axial stress compression modes were validated by comparing numerical predictions, which were based on them, to experimental results.