Experimental and Numerical Characterization of the Cyclic Thermomechanical Behavior of a High Temperature Forming Tool Alloy

This paper describes high temperature cyclic and creep relaxation testing and modeling of a high nickel-chromium material (XN40F) for application to the life prediction of superplastic forming (SPF) tools. An experimental test program to characterize the high temperature cyclic elastic-plastic-creep behavior of the material over a range of temperatures between $20°C$ and $900°C$ is described. The objective of the material testing is the development of a high temperature material model for cyclic analyses and life prediction of SPF dies for SPF of titanium aerospace components. A two-layer viscoplasticity model, which combines both creep and combined isotropic-kinematic plasticity, is chosen to represent the material behavior. The process of material constant identification for this model is presented, and the predicted results are compared with the rate-dependent (isothermal) experimental results. The temperature-dependent material model is furthermore applied to simulative thermomechanical fatigue tests, designed to represent the temperature and stress-strain cycling associated with the most damaging phase of the die cycle. The model is shown to give good correlation with the test data, thus vindicating future application of the material model in thermomechanical analyses of SPF dies for distortion and life prediction.