MODELING OF AN AUSTENITIC STAINLESS-STEEL AT HIGH-TEMPERATURE UNDER IN-PHASE AND OUT-OF-PHASE CYCLIC TENSION-TORSION LOADING

Results are presented for experiments performed on austenitic stainless steel type 316 L at a temperature of 600 degrees C. The tests were carried out under both unidirectional (1D) and bidirectional (2D) cyclic tension-torsion loading, both in and out of phase and with one (in the case of 2D ratcheting) or two cyclic components. For the 2D loadings, it is shown that a weak supplementary hardening Delta H+ appears that is primarily a function of the phase difference Phi between the strain components, and the ratio R between the maximum amplitudes of these components. These observations conform qualitatively with those already reported for ambient temperatures; but quantitatively it is shown that the maximum amplitude of this supplementary hardening is a sharply decreasing function of the temperature. A simple phenomenological formulation is proposed which, when integrated into a unified visoplastic model, developed elsewhere, leads to a good representation of the experimental results under cyclic 1D and 2D loadings. The model describes the effects due to the loading rate, the phase difference between the two cyclic components, and the 2D tensile-torsion ratchet.