Influences of Cyclic Pre-Overload on Low Cycle Fatigue Behaviours of Elbow Pipe Available to Purchase

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. The preliminary fatigue tests were conducted under constant cyclic displacements. Then, two test conditions were adopted to investigate the influence of cyclic pre-overload on low cycle behavior of elbow on the basis of the preliminary test results. The fatigue test results were evaluated by using the total usage factor UF_Total (= UF_pre+UF_post), where the UF_pre and UF_post correspond to usage factor for δ_pre and δ_post, respectively. The fatigue lives of overloaded elbow pipes were estimated based on the cumulative fatigue damage rule basically from UF_pre = 0.2 to UF_pre = 0.6. 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.