Experimental And Failure Model Study Of Low Cycle Fatigue Considering Ratcheting Effect

Engineering structure components often subjected to cyclically varying loads with non-zero mean stress. For stress-controlled cycling with non-zero mean stress, a cyclic accumulation of inelastic deformation will occur, which is called ratcheting. Additional damage can be caused by the accumulated ratcheting strain, resulting in shorter fatigue lives. It follows that for the stress-controlled mode ratcheting effects should be taken into account in the fatigue failure model. Thus systematical studies on the effect of ratcheting on fatigue life and failure model have not only the scientific significance, but also a practical value.A number of uniaxial stress-controlled low cycle fatigue experiments were conducted for SS304 stainless steel, 42CrMo steel with annealing and tempering heat-treatment at room temperature. The ratcheting behaviour, fatigue failure and their interaction were systemically investigated in different loading levels. The effects of mean stress, stress amplitude and stress ratio on the ratcheting strain and fatigue life were discussed. The experimental results show that the ratcheting strain and fatigue life of the material depend greatly on mean stress, stress amplitude and stress ratio of uniaxial cyclic stressing, tow kinds of failure modes (i.e., ratcheing failure with obvious neching due to large ratcheting strain and fatigue failure due to low-cycle fatigue caused by fatigue crack) take place respectively, depending on the stress level prescribed in the tests.A ratchting strain rate-life model and a fatigue-ratcheting linear interaction model were proposed in this work. The predicted results by fatigue-ratcheting linear interaction model show good agreement with experimental ones.