Investigation of low cycle asymmetric torsion

Abstract

The presented paper considers low cycle fatigue of the grade 45 steel under symmetric (= -1.0) and asymmetric (= -0.75; -0.5) stress limited torsion. It was defined, that the material is cyclically stable, because the hysteresis loop width during symmetric and asymmetric loading cycles is constant. Under the symmetric cyclic loading, the plastic strain is not accumulated, i.e. qua-sistatic damage does not occur, whereas under the asym-metric loading the accumulation of plastic strain takes place. The analytical dependences were proposed to calcu-late the fatigue life under asymmetric loadings, taking into account the fatigue and quasi-static damage due to accu-mulated plastic strain. It was determined, that quasistatic damage increases, while loading level increases and results at the middle levels decrease of the fatigue life from = = 2840 to = 1830 (τrτrcNcNτ=1.60; = -0.75) and from = 9050 to = 5010 (τrcNcNτ= 1.60; = -0.5).