The Chaboche hardening rule: A re-evaluation of calibration procedures and a modified rule with an evolving material parameter

• Calibration procedures of Chaboche hardening models are investigated.
• It is shown that some of the methods may yield physically unacceptable predictions.
• An alternative modified calibration methodology has been suggested.
• A modified Chaboche rule with an evolving material parameter has been proposed.
• The model is shown to be more successful in the simulation of ratcheting strains.

This study first re-examines key existing calibration procedures for the Chaboche decomposed nonlinear kinematic hardening rule. Special attention has been paid to the extent to which the predictions of calibrated models represent the physics of phenomena observed in strain- and stress-controlled cyclic tests. It has been shown and discussed that newer methods suffer from some weaknesses and may yield nonphysical results. Second, with the aim of improving the accuracy of its ratcheting strain predictions in unsymmetric stress-controlled tests, a modified calibration procedure and a new Chaboche hardening rule with an evolving material parameter is introduced. The former improves the accuracy of predicted ratcheting strains at the initial cycles, while the latter is responsible for the better agreement of the results at the higher cycles. The new model assumes there exists a linear relationship between one of the coefficient of the model and its corresponding effective/equivalent backstress. Finally, the predictions of the new model and those of the original Chaboche rule are compared with the available experimental results from the literature. It has been shown that, regardless of the level of mean stress of unsymmetric stress-controlled test, the ratcheting rates of the higher cycles are satisfactorily predicted by the proposed modified model.