Analysis on the Dependence of the Fracture Locus on the Pressure and the Lode Angle

Abstract

Classical fracture models assume that the stress triaxiality is the key parameter controlling the magnitude of the fracture strain. However, recent works shown the influence of other parameters that characterize the stress state on the prediction of fracture strains. In this work, two uncoupled fracture models, Mae and Wierzbicki [8] and Xue and Wierzbicki [9], were analysed using finite element models. These models define a ductile fracture locus formulated in the 3D space of the stress triaxiality, Lode angle parameter and the equivalent fracture strain. The material selected was a cast A356 aluminium alloy for which the model parameters were previously defined. Two groups of tests are analysed in order to provide additional information on the material ductility. The first corresponds to plane strain tests carried out on flat plates with different grooves. The second corresponds to uniaxial tension tests applied on smooth and notched round bars, which were designed with different notch radii. These specimens allow covering a wide range of stress triaxiality. The present work extracts the evolution of the equivalent plastic strain at fracture, the stress triaxiality and the Lode angle parameter in order to evaluate the possibility of using either smooth and notched bars tests or smooth and notched bars tests and grooved plates to evaluate the 3D locus for high values of stress triaxiality. In this context, a new function is proposed to describe the equivalent plastic strain at fracture based on the stress triaxiality and the Lode angle parameter.