A local viewpoint for evaluating the influence of stress triaxiality and lode angle on ductile damage and hardening

All damage and failure models, describing either the evolution of microvoids, the developmentof shear bands or local rupture, rely on the knowledge of the hardening function atlarge plastic strains which, then, becomes an essential prerequisite for any failure prediction.The phenomenon of ductile failure is analyzed here by focusing on its relationship withthe variables for the stress–strain characterization, and by discussing the influence of plasticstrain, stress triaxiality and Lode angle parameters on both the above aspects of materialsbehavior.Failure predictions are presented for different metals and different combinations of loadspecimengeometry, according to three theories (the Tresca criteria and two models byWierzbicki et al.) and to a procedure previously developed for the stress–strain characterizationin the post-necking range.Experimental tests are performed by pulling tensile specimens and notched flat samplesup to failure, then finite elements simulations are used to calculate the required failurerelatedvariables within the volume of failing specimens; the results of the failure calculationsare compared each other and with experimental data, and a discussion about thepeculiarities of the methods used for predicting failure is also provided.