A multiaxial cyclic plasticity model for non-proportional loading cases

Abstract

Abstract The hardening behavior of metals to non-proportional loading and ratchetting effects is investigated here using the proposed model presented by Voyiadjis and Basuroychowdhury (1998) . The backstress evolution equations are modified here in order to account for non-proportionality of loading. The same general form of the kinematic hardening formulation defined previously by Voyiadjis and Basuroychowdhury (1998) is used here. The material constant, β ( i ) , is now expressed in a functional form, β (i) , to account for the variation in the loading direction. Numerical results are obtained using the proposed model for a series of plastic strain controlled cyclic tests due to multiaxial cyclic tests performed at room temperature on thin-walled tubural specimens of Type 316 stainless steel. The results are compared with the experimental values obtained by Tanaka, et al. (1985) . The drift correction due to the finite increments of stress or strain is corrected using an efficient approach that corrects the backstress only. The model is also tested for cyclic creep which occurs due to a non-zero mean stress. The cyclic creep occurs initially and saturates reaching a stable cycle.The modified proposed kinematic hardening rule and the associated bounding surface are used in conjunction with a robust plasticity model for metals. The hardening dependence on the plastic strain path is also investigated in this work.