Abstract
Low cycle fatigue strength of elbow piping subjected to in-plane cyclic bending displacement is extremely less than the best fit fatigue curve or the Manson's fatigue curve of the test material. Reduction of fracture ductility under multi-axial stress state significantly increases ductility exhaustion rate. This new finding means that effect of multi-axial stress degree should be included in the low cycle fatigue evaluation of elbow piping. From this view-point, the author developed a new cumulative damage rule considering multi-axial stress degree in order to explain the reason of fatigue strength reduction of elbow piping. Also he developed the advanced revised universal slope method to estimate actual fatigue life of elbow piping considering multi-axial stress degree. He believes that development of multi-axial fatigue evaluation method considering reduction of fracture ductility is useful not only for structural integrity of elbow piping but also that for other structures and components subjected to severe loading. Accordingly, he summarizes the logics and procedures of above-mentioned fatigue evaluation methods as a reference for future research on the multi-axial low cycle fatigue evaluation.
