Low cycle fatigue tests and finite element analysis were conducted using 100A elbow specimens made of STPT410 steel. The elbows were subjected to cyclic in-plane bending under displacement control without or with inner pressure of 9 MPa. Initially, fatigue tests were conducted under constant cyclic displacements. Then, two step cyclic fatigue tests were carried out to investigate the effect of cyclic overload on low cycle fatigue behavior of elbows. Consequently, the fatigue lives of elbows in two step fatigue tests can be estimated by the Miner's rule. However, in this evaluation, the experimental fatigue lives under constant cyclic displacements are necessary to calculate the usage factors. So the fatigue lives under constant cyclic displacements were calculated on the basis of the universal slope method and the revised universal slope method. Then, the usage factors of the two step cyclic fatigue tests were estimated by these calculated fatigue lives and the Miner's rule. As a result, the usage factor calculated based on the universal slope method were estimated on unconservative side. On the other hand, the usage factors calculated based on the revised universal slope method were close to UF_<Total>=1. Thus, the residual fatigue lives can be predicted with a high degree of accuracy by using the revised universal slope method and the Miner's rule.
