Unified constitutive modeling of Haynes 230 including cyclic hardening/softening and dynamic strain aging under isothermal low-cycle fatigue and fatigue-creep loads

Abstract

A unified viscoplastic constitutive model with wide temperature adaptability is developed based on the basic framework of the Chaboche type model to capture the intricate cyclic viscoplastic behaviors of Haynes 230 subjected to isothermal low-cycle fatigue and fatigue-creep loads. By introducing effective aging time into drag stress in the hyperbolic sine viscosity function, the critical value of back stress and the additional hardening model, a rate-dependent model based on the dimensionless concentration of solute atoms or precipitates is further improved to realize simulation of dynamic strain aging effects. A multistage evolutionary approach to determining asymptotic value of back stress influenced by strain range and cumulative plastic strain is proposed to respond to cyclic hardening or softening evolved differently with the variation of temperature. For the fatigue-creep interaction, a rate or time dependent directional hardening cumulative model combined with the existing mean stress model is established. After the multi-step material parameter determination method is given, the capabilities of the proposed model are fully validated to accurately depict the mechanical behaviors of Haynes 230 for five representative temperatures.