Modified GTN model for a broad range of stress states and application to ductile fracture

• A modification to GTN model is proposed for simulating ductile fracture under high, low and negative stress triaxialities.
• Two distinctive damage parameters are introduced into yield function to capture the degradation process.
• A new function of triaxiality and Lode angle is adopted as shear damage weight function.
• The accuracy of new model is validated by the experimental data of specimens covering a broad range of stress states.

Based on two ductile fracture mechanisms, a new modification to the Gurson–Tvergaard–Needleman (GTN) model is proposed for the simulation of ductile fracture behaviors under high, low and negative stress triaxiality loadings. In the modified GTN model, two distinctive damage parameters, respectively related to void growth mechanism and void shear mechanism, are introduced into yield function as internal variables of degradation process. The void volume fraction, similar to the original GTN model, is still adopted to capture the volumetric damage due to the void nucleation, growth and subsequent inner-necking, which plays the main role in tension. The additional shear damage, due to void rotation, distortion as well as “void sheet” effects, can accumulate in different stress states, even under negative stress triaxiality with the auxiliary of a new stress–state dependent function. The development of numerical procedures into finite element platform ABAQUS/Explicit allows the analysis of damage evolution, crack initiation and growth. The validity of the new model is examined by comparing numerical results with the experimental data of specimens including axisymmetric tensile bar, flat grooved plate, torsion tube and compression cylinder. The results show that the modified GTN model performs well in predicting the overall load–displacement responses and fracture paths of various specimens under stress states covering a wide range of triaxiality and Lode parameter combinations.