On the extension of the Gurson-type porous plasticity models for prediction of ductile fracture under shear-dominated conditions

• Two damage parameters representing the volumetric damage and the shear damage are considered.
• The GTN model is extended by coupling the two damage parameters into the yield function and flow potential.
• The effectiveness of the new model is illustrated through a series of numerical tests.
• The modified GTN model is applied to predict the ductile fracture behavior of a Zircaloy-4.
• The calibrated model predicts failure initiation and propagation in various specimens.

One of the major drawbacks of the Gurson-type of porous plasticity models is the inability of these models to predict material failure under low stress triaxiality, shear dominated conditions. This study addresses this issue by combining the damage mechanics concept with the porous plasticity model that accounts for void nucleation, growth and coalescence. In particular, the widely adopted Gurson–Tvergaard–Needleman (GTN) model is extended by coupling two damage parameters, representing the volumetric damage (void volume fraction) and the shear damage, respectively, into the yield function and flow potential. The effectiveness of the new model is illustrated through a series of numerical tests comparing its performance with existing models. The current model not only is capable of predicting damage and fracture under low (even negative) triaxiality conditions but also suppresses spurious damage that has been shown to develop in earlier modifications of the GTN model for moderate to high triaxiality regimes. Finally the modified GTN model is applied to predict the ductile fracture behavior of a beta-treated Zircaloy-4 by coupling the proposed damage modeling framework with a recently developed J2–J3 plasticity model for the matrix material. Model parameters are calibrated using experimental data, and the calibrated model predicts failure initiation and propagation in various specimens experiencing a wide range of triaxiality and Lode parameter combinations.