On multiaxial creep–fatigue considering the non-proportional loading effect: Constitutive modeling, deformation mechanism, and life prediction

Abstract

In this paper, a series of strain-controlled fatigue and creep–fatigue tests under proportional/non-proportional loadings were performed for type 304 stainless steel at 873 K. Then, post-test metallographic observations were performed through the electron back scattered diffraction (EBSD) and transmission electron microscope (TEM) combinative characterizations. In this aspect, the wavy slip dominated deformation mechanism under non-proportional loadings was considered as the essence for additional hardening, while the introduction of creep resulted in further microstructure evolutions by facilitating recrystallization. Afterward, a unified viscoplasticity constitutive model was proposed to simulate the cyclic stress–strain responses, in which an additional hardening parameter combined with a loading-path parameter was used to describe the cyclic hardening curves. Concurrently, stress triaxiality was introduced to provide accurate descriptions for the stress relaxation behavior. Semi-physical continuum damage models involving multiaxial damage factor and non-proportional strain energy parameter was proposed to predict the multiaxial creep–fatigue damage evaluations. Good agreements between experimental data and simulated results were achieved with the help of the proposed numerical procedures.