Comparative Study of Effect of Porosity on Tensile and Shear Ductility in A356 Cast Aluminum Alloy by Finite Element Simulation

Abstract

Three kinds of microstructural finite element (FE) models are constructed based on the fracture surfaces with different level of porosities. The tensile and shear loadings are applied on three kinds of FE models. The fracture criterion used in the present FE analysis is the ductile fracture locus formulated in the space of the stress triaxiality and the plastic strain to fracture. Based on the FE simulation results, a linear relationship between the material ductility and the area fraction of the defects is tentatively constructed. It is found that the shear ductility decreases at a slightly faster rate than the tensile ductility with the increasing area fraction of the defects. Finally, the effective plastic strain as a function of the stress triaxiality up to fracture at the crack initiation point is compared for three kinds of microstructural FE models under tensile and shear loadings. As a result, it appears that the increase of the area fraction of the defects enhances the evolution of the local stress triaxiality under both shear and tensile loadings. In addition, the local stress triaxiality at the crack initiation point changes in the smaller range under shear loading than under tensile loading. It is found that the difference of the evolution of the local plastic strain and local stress triaxiality should lead the different sensitivity of the shear and tensile ductility to the area fraction of the defects.