Macroscopic behaviour of porous metals with internal gas pressure under multiaxial loading conditions

The gas pressure build up within closed cells or dynamic intercellular air flow in open-cells foams influences the macroscopic behaviour during the deformation. Two dimensional numerical simulations for simple cell shapes point out that an internal pressure delays the onset of yielding in the cell walls during compressive load. Another important process affected by internal pore pressure is the roll forming of structurally porous metals. During pressing and thermo-mechanical forming the internal pressure of the pores and the temperature can raise to high values. One can find also in the literature that there is no essential influence on the forming response for gas pressure about half the yield strength of the fully dense matrix material. In this paper, the influence of internal gas pressure on the mechanical behaviour of porous metals under differing loading conditions is numerically investigated. It is found that the internal gas pressure influences rather significantly the initial yielding and the macroscopic behaviour also if the pressure is clear less than a half of the yield strength of the base material.