Void growth and coalescence in sigmoidal hardening porous plastic solids under tensile and shear loading

Abstract

This work examines the void growth and coalescence in isotropic porous elastoplastic solids with sigmoidal material hardening via finite element three-dimensional unit cell calculations. The investigations are carried out for various combinations of stress triaxiality ratio (T ) and Lode parameter (L) and considers a wide range of sigmoidal hardening behaviors with effective hardening rates spanning two decades. The effect of L is considered in the presence and in the absence of imposed shear stress. Our findings reveal that depending on the rate of sigmoidal hardening the cell stress-strain responses may exhibit two distinct transitions with respect to stress triaxiality T . Further, the sigmoidal hardening rate also influences porosity evolution which may show stagnation before a runaway growth up to final failure. For a given T -L combination, an imposed shear stress exacerbates the onset of coalescence relative to its counterpart with no imposed shear stress. We find that the residual cell ductility beyond the onset of coalescence is strongly influenced by the effective material hardening rate at high triaxiality levels.