Extension of a shear-controlled ductile fracture criterion by considering the necking coalescence of voids

An isotropic ductile fracture criterion considering nucleation, growth, shear coalescence and necking coalescence of voids during plastic deformation is developed to model fracture behavior of ductile metals. The innovation of this fracture criterion is that it considers the mechanism of necking coalescence of voids on the basis of a shear-controlled ductile fracture criterion developed by the micro-mechanism (Lou et al., 2014). The damage from coalescence of voids is expressed as the sum of the damages from the shear coalescence of voids and necking coalescence of voids. We assume that the damage from necking coalescence of voids is controlled by the normalized normal stress at the maximum shear plane, the larger positive normalized normal stress at the maximum shear plane will promote the necking coalescence of voids, while the negative gives no effect on the necking coalescence of voids. After the establishment of the proposed fracture criterion, a detailed parametric study is performed to demonstrate the flexibility of the proposed criterion. Then, the proposed ductile criterion is employed to construct fracture loci for three different materials (AA 2024-T351, AA 6060-T6 and A710 steel). And fracture loci constructed are compared with those experimental data points to validate the performance of the proposed fracture criterion. For the purpose of comparison, the predicted results are compared with those predicted by the micro-mechanism-motivated criterion (Lou et al., 2014), the modified Mohr-Coulomb criterion (Bai and Wierzbicki, 2010). The better agreement of the predictions with the experimental data demonstrates that the proposed fracture criterion is able to improve the prediction accuracy for different metals under various stress states and the mechanism of necking coalescence exhibits a noticeable role in predicting the ductile fracture. Moreover, the proposed criterion is expected to be employed in finite element simulation to calculate the ductile fracture for different metals due to the high accuracy.