Design fatigue curves of new concept were developed in the Subcommittee on Design Fatigue Curve in the Atomic Energy Research Committee in the Japan Welding Engineering Society (JWES). Also, Working Group on Design Fatigue Curves (WG DFC) in the JSME studied the validity and the applicability of the design fatigue curves developed in the JWES to incorporate into the JSME Environmental Fatigue Evaluation Method, and the design fatigue curves developed in the JWES were improved.The improved design fatigue curve consists of the best-fit curves using tensile strength as a parameter, correction of mean stress effect employed the Smith-Watson-Topper approach, surface finish effect employed a developed fatigue strength reduction factor in the JSME and variable loading amplitude effect. This paper explains the treatment of variable loading amplitude effect in the improved design fatigue curves.The improved design fatigue curves have employed the method of variable loading amplitude effect in EN 13445. This method uses a fatigue life exponent of −0.1 from N = 2×106. Study Group on Fatigue Strength in the JSME performed a campaign of fatigue tests for variable loading amplitude and the test data showed the fatigue life exponent was −0.07. This outcome of the JSME LF committee can support the fatigue life exponent of −0.1 in EN 13445.Also, the maximum number of cycles of the improved design fatigue curves has decided as 108 cycles, which is the same as EN 13445. The number of 108 cycles is supported by the high cycle experimental fatigue data and the JWES subcommittee confirmed that the cut-off number of cycles did not give an influence on the cumulative usage factors of typical components when considering not only design transients but also thermal fluctuation.

Development of New Design Fatigue Curves in Japan – Treatment of Variable Loading Amplitude Effect

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

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