多軸応力度を考慮した低サイクル疲労評価法再考

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 because of damage of cumulative strain. However, it is very difficult to calculate accurate cumulative strain by the conventional multi-purpose structural analysis codes. The author proposes to estimate equivalent cumulative strain by combining the advanced revised universal slope method with the cumulative damage rule considering multi-axial stress degree. He also discusses the reason why the accuracy of the proposed method reduces in the region of high fatigue damage ratio Df and an example of engineering application of the proposed method. Finally, he discusses the margin of the ASME design fatigue curve from the view-point of the cumulative damage rule considering multi-axial stress degree.