On the performance of kinematic hardening rules in predicting a class of biaxial ratcheting histories

It is well known that strain-symmetric axial cycling of thin-walled metal tubes in the presence of pressure results in a progressive accumulation (ratcheting) of circumferential strain. It was previously demonstrated that the prediction of the rate of ratcheting under constant internal pressure, by nonlinear kinematic hardening models, is very sensitive to the hardening rule adopted. It was shown that the Armstrong-Frederick hardening suitably calibrated and used in a class of models can yield reasonably good predictions of the rate of ratcheting for a range of cycle parameters. In this paper, the subject is revisited in the light of further experimental results involving simultaneous cycling of the internal pressure and the axial strain. Experiments and analyses were performed for a family of five such biaxial loading histories. A similar sensitivity to the kinematic hardening rule used in the models was observed in all the new loading histories. Furthermore the hardening rule calibrated in the constant pressure experiments was found to yield accurate predictions for three of the loading histories considered and poor predictions for the other two. The reasons for this varied performance are analyzed and some recommendations for implementation of such models in structural applications are made.