The effect of internal pressure in gas pores containing materials on their mechanical stability under shear

Metallic structures, produced by high pressure die-cast or powder bed fusion additive manufacturing techniques often contain gas pores. While under high triaxial stress states the effect of internal pressure can be superimposed on top of the applied stress field, thus resulting in a shift of the flow potential along the hydrostatic axis, under zero triaxiality deformation (i.e. shear) it is not quite obvious. The aim of this study is to analyse the overall mechanical behavior of such material when subjected to shear deformation. Two dimensional finite element calculations on a material containing a periodic array of pressurized voids are used for this analysis. It was found that with increasing internal pressure, the void's shape tends to remain elliptical and the appearance of stress concentrations, associated with the well know s-shape of sheared voids is delayed. This in turn, leads to a competition between two possible nucleation sites for strain localization. The combined effect of internal pressure and strain hardening was investigated through a parametric study and general conclusions are drawn.