A study of cyclic plasticity and viscoplasticity in a new nickel-based superalloy using unified constitutive equations. Part I: Evaluation and determination of material parameters

Cyclic plasticity and viscoplasticity of a new nickel-based superalloy have been studied using the Chaboche unified constitutive equations. The material parameters in the Chaboche model were evaluated by deriving the response sensitivities for typical load paths. This has facilitated the design of an efficient test matrix and the development of a gradient-driven, non-linear optimisation algorithm. Experiments were carried out to obtain cyclic stress–strain curves at three strain-rates, multiple hardening and stress relaxation curves, as well as cyclic tests with strain hold periods introduced at maximum and minimum strains. The latter served as bench tests to evaluate the model capacity in the prediction of creep–fatigue interaction. Simulations of cyclic stress–strain, stress hardening and relaxation behaviour were compared favourably with the experimental results, although the prediction of cyclic stress relaxation was less satisfactory, a subject to be explored in Part II of this paper.