Constitutive Modeling of TMF and Creep-Fatigue of a Ni-Base Alloy

Abstract

Abstract Engineering materials are often subjected to high temperatures and varying mechanical load, making them display both creep and fatigue. Viscoplastic models have been an attractive way to simulate the behavior of materials under these conditions due to their ability to capture the hysteresis, load rate, and stress relaxation effect exhibited by materials. Nickel-base alloys experience widespread use throughout pressure vessels and turbomachinery due to their ability to retain high strength at high temperature. In this study, the low-cycle fatigue (LCF), thermo-mechanical fatigue (TMF), and creep-fatigue (CF) of candidate material IN617 is modeled using the Chaboche viscoplasticity model. The Chaboche model is implemented using three non-linear kinematic hardening terms with static recovery included as well as nonlinear isotropic hardening. Methods for finding the kinematic and isotropic hardening from Ramberg-Osgood constants are presented to allow for model development to encompass all available data instead of fitting to specific data sets. A novel method for fitting the static recovery portion of the model from creep data is presented, allowing for the capture of complex loadings such as CF from standard creep tests. New temperature-dependent formulations of the Chaboche constants are presented for IN617. The model is compared to available test data and simulations are presented to show future experiments that could be run to further validate or improve the model.