Synergistic effects of plastic anisotropy and void coalescence on fracture mode in plane strain

Abstract

The macroscopic fracture in plane strain is known to be shear-like in ductile materials.In most structural materials, fracture starts after diffuse necking,at the centre of the specimen, by micro-void coalescence giving rise afterwards tothe macroscopic shear fracture mode.In this paper, the effect of coalescence on shear band development and on associated fracture mode in plane strain is analysed numerically.The calculations are performed using a recent elastic-viscoplasticGurson-like model that accounts for void shape evolution, coalescenceand post-coalescence micromechanics along with isotropic hardeningand orthotropic plasticity for the matrix behaviour. The latter is introduced to represent the actualflow properties of hot-worked materials.No kinematic hardening or nucleation formulation is used in orderto focus attention on coalescence effects and to discuss, with respectto experiments, published results based on kinematic hardeningand nucleation effects.The most important finding is the synergistic effect of plasticanisotropy and post-coalescence yield surface curvatureupon the onset of a shear band after the fracture sets in at thecentre of the specimen.