Elastoplastic mechanics of porous materials with varied inner pressures

A micromechanics model and a computational homogenization method were developed to examine the macroscopic elastoplasticity and yield behavior of closed-cell porous materials with varied inner gas pressures. For the uniaxial stress-strain relation of the porous material, the micromechanics model coincides well with the numerical homogenization, especially for the case of relatively low porosity and gas pressures. The effects of the combination of the different gas pressures on the uniaxial stress-strain curve, the nominal Poissons ratio, yield surface and initial yield strength of the material are systematically investigated. The multiple gas pressures can induce the tension-compression asymmetry of the uniaxial stress-strain curves and the nominal Poisson's ratio of nonlinear deformation. In particular it is shown that when the multiple gas pressures coincide, the yield surface of the porous material with inner gas pressures can be simply obtained from that of the porous material without inner pressures by a shift along the negative direction of the hydrostatic stress axis. However, when the multiple pressures are different, in addition to a translation along the hydrostatic axis, the yield surface undergoes a change in shape and size, and the maximal equivalent stress is lowered by a difference in gas pressures. Furthermore, the multiple gas pressures have a significant effect to reduce the yield strength of the closed cell porous materials.