Abstract
Low cycle fatigue tests were conducted using sound elbows made of carbon steel (STPT410). The elbows were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. Initially, fatigue tests were conducted under constant cyclic displacements. Then, two step fatigue tests were carried out to investigate the influence of cyclic pre-overload on low cycle behavior of elbow on the basis of the previous test results. The fatigue test results were evaluated by using the total usage factor UF_<total> (=UF_1+UF_2), where the UF_1 and UF_2 correspond to usage factor for δ_1 andδ_2, respectively. The residual fatigue life overloaded pipe in UF_1=0.6 was evaluated on non-conservative side by the cumulative fatigue damage rule. On the other hand, the residual fatigue lives in the range of UF_1≦0.4 can be estimated based on the cumulative fatigue damage rule generally. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.
