Cyclic Creep Behavior and Unstable Fracture under True Stress Controlled Cyclic Condition

Cyclic creep behaviors of material have generally been studied by the load controlled tension-compression low-cycle fatigue tests. The results obtained by the load controlled tests include the effect of the increase of the maximum tensile stress due to the progress of axial strain, in addition to the effect of cyclic softening of the material. To separate the two effects clearly, true-stress controlled cyclic tension-compression tests are made with brass and the results obtained are compared with those by the load controlled tests. Cyclic creep curves under true-stress controlled condition are found to consist mainly of the primary transient and the secondary steady stages, with lack of the tertiary accelerating stage. Cyclic creep characteristics are formulated as a function of the maximum cyclic stress and the number of cycles. A criterion of the unstable fracture under cyclic creep is also given.