Rupture mechanisms in combined tension and shear—Micromechanics

Abstract

A micromechanics model based on the theoretical framework of plastic localization into a band introduced by Rice is developed. The model consists of a planar band with a square array of equally sized cells, with a spherical void located in the centre of each cell. The periodic arrangement of the cells allows the study of a single unit cell for which fully periodic boundary conditions are applied. The micromechanics model is applied to analyze failure by ductile rupture in experiments on double notched tube specimens subjected to combined tension and torsion carried out by the present authors. The stress state is characterized in terms of the stress triaxiality and the Lode parameter. Two rupture mechanisms can be identified, void coalescence by internal necking at high triaxiality and void coalescence by internal shearing at low triaxiality. For the internal necking mechanism, failure is assumed to occur when the deformation localizes into a planar band and is closely associated with extensive void growth until impingement of voids. For the internal shearing mechanism, a simple criterion based on the attainment of a critical value of shear deformation is utilized. The two failure criteria capture the transition between the two rupture mechanisms successfully and are in good agreement with the experimental result.

Damage prediction in single point incremental forming using an extended Gurson model

“…The third invariant (related to the Lode angle) of the deviatoric stress has been considered in constitutive models to predict localization (Brünig et al, 2000) and fracture (Bai and Wierzbicki, 2008). Barsoum and Faleskog (2007) showed that the strain localization decreases when passing from tension to shear, and the softening rates decreases when increasing the Lode parameter. Gao et al (2009) demonstrated that the Lode parameter has an important effect on the strain at coalescence and this effect is lower at high triaxiality, coinciding with the previous results from Zhang et al (2001).…”

On the description of ductile fracture in metals by the strain localization theory

“…Moreover, with the variations of materials, specimen geometries, boundary conditions and measurement techniques in the literature, different conclusions can be obtained on the characteristics of ductile failure. For instance, the ductile failure strain under low stress triaxiality conditions was found to exhibit a nonmonotonic dependence to the stress triaxiality by Bai and Wierzbicki (2010) and Barsoum and Faleskog (2007), while a monotonic dependence was found by Haltom et al (2013), Ghahremaninezhad and Ravi-Chandar (2013) and Papasidero et al (2014).…”

Experimental characterization and numerical modeling of micromechanical damage under different stress states

“…Recently, several studies [12][13][14][15][16][17][18][19][20][21] have shown that the Lode angle, associated with the third invariant of the deviatoric stress tensor, is an essential parameter in ductile fracture. It characterizes the effect of the stress state on plastic flow and the ductile rupture of the material.…”