2段多重繰返し試験における微小き裂の挙動と累積疲労損傷値の変動

概要

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The Correlation between behavior of small fatigue cracks and variation of cumulative fatigue damage under the multiple repeated two-step stress loading was investigated by using specimens with an initial small crack. Various combinations of the overstress σ_H and the understress σ_L cause various values of cumulative fatigue damage. The critical stress σ_<wi> for fatigue crack initiation from a small crack is the important measure to evaluate the contribution of σ_L on fatigue damage. The values of cumulative fatigue damage D based on the Modified Miner Rule became much smaller than 1.0 for a certain combination of σ_H and σ_L. The minimum value of D obtained in the present study was D≅0.18. Although a wide scatter of D has been reported by many studies, it is not caused by statistical scatters of a material but caused by various combinations and sequence of σ_H and σ_L in relation to crack size at every moment. The possible minimum value of D(D_<min>) for a definite cycle ratio of σ_H and σ_L under various combinatons of sequence of loadings can be predicted by the method proposed in the present study and D_<min> will be useful for the design under variable amplitude loadings.
社団法人日本材料学会の論文
1989-10-15