Chaboche Kinematic Hardening Model for Cyclic Ratcheting Simulation: Continuous and Discontinuous Hardening Materials

ASME Code Case N-900 and JSME Code Case NC-CC-008 present fatigue evaluation methods based on elastic-plastic analysis. While the ASME Code Case does not specify any cyclic hardening model for finite element analysis, the JSME Code Case recommends a bi-linear kinematic hardening model. However, the bi-linear model is inadequate for predicting cyclic ratcheting behavior in piping systems, highlighting the need for a kinematic hardening model with nonlinear backstress terms, such as the Chaboche model. Due to the numerous parameters involved in the Chaboche model, a systematic determination procedure is required. This paper proposes a parameter determination procedure for the Chaboche kinematic hardening model with three nonlinear backstress terms, using monotonic true stress–true plastic strain curve and analytical formulas. The method is applicable to both continuous yielding materials (stainless steel) and discontinuous yielding materials (carbon and low-alloy steel). To validate the procedure, load-controlled cyclic loading tests were performed on notched bar specimens made of low-alloy and stainless steels, under various load ratios. Finite element simulations were conducted using both the bi-linear and Chaboche models with parameters determined according to the JSME Code Case and the proposed method, respectively. The simulation results showed that the bi-linear model failed to predict ratcheting behavior, whereas the Chaboche model estimated the ratcheting behavior conservatively in all cases examined. However, further research of application to piping system analysis would be needed to ensure general applicability.