Application of an extended void growth model with strain hardening and void shape evolution to ductile fracture under axisymmetric tension

The version of the Gurson model adapted by Tvergaard is extended by fitting, based on numerical results proposed in the literature, the tuning parameters q1 and q2 in order to better capture the effects of the strain hardening and void shape evolution. The model is completed by two types of analytical void coalescence criteria, one for internal necking (Thomason 1968 and 1990) and one for void sheet (McClintock 1968). The validity of the proposed formulation is realized through comparison with more elaborate finite element models found in the literature. Using an approximate description of the variation of the stress triaxiality in the minimum section of an axisymmetric necking zone, the void growth rates and fracture strains are predicted. These are evaluated for several ductile alloys for which the experimental micro-mechanical data are reported in the literature.