A new yield criteria including the effect of lode angle and stress triaxiality

According to several experiments reported in the literature, the elastoplastic behaviour of metals depends not only on the firststress invariant (triaxiality) for the ductile damage and on the second stress invariant (equivalent von Mises stress) for the yield,but also on the third stress invariant (normalized Lode angle X) which may affect at the same time the yielding and the ductilefailure.In this paper a new yield model is presented, where the yield surface depends on the Lode Angle and, eventually, also on thetriaxiality ratio.The proposed model is identified by a calibration parameter expressing the degree of nonlinearity of the yield with respect to theLode angle, and a calibration function expressing the maximum variability of the hardening stress at the two extremities of theLode angle range, corresponding to the uniaxial and to the pure shear stress states.