Strain and stress controlled low cycle fatigue behaviors of TC21 alloy

In this article the strain controlled and stress controlled low cycle fatigue behaviors of TC21 titanium alloy were investigated. The fatigue tests were performed at room temperature and cyclic strain and stress ratio of 0.1 with triangle load wave. During the initial stage of strain controlled fatigue, the cyclic tensile stresses soften rapidly and the cyclic compressive stresses harden rapidly at the same time, the rates of cyclic softening and cyclic hardening decrease with the fatigue progress. During the overall fatigue progress, the soften rate is related to the cyclic strain but little to the cyclic stress, which is related to the macro friction stresses. Obvious cyclic creep occurs under the stress controlled low cycle fatigue conditions, and the magnitude of cyclic creep strain is related to the maximum cyclic stress. The softening of tensile friction stresses is the main factor of cyclic creep.