疲労過程を考慮した場合の実働荷重疲労強度の推定

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A fatigue process consists of crack initiation and crack propagation. So the authors have tried to estimate the fatigue life to failure, N_f, as the sum of the crack initiation life N_i and the crack propagation life N_p. The authors also assumed that the effect of the mean stress on the fatigue damage is different in each of these two processes. Then, the actual service load patterns have been analysed by applying the range-pair-mean count method as follows. Each stress range pair σ_a with mean stress levelσ_m, that is S(σ_a, σ_m), is translated into a stress amplitude σ_t by taking σ_<ti>=σ_a+mσ_m, where m=0.4σ_w/σ_s, in the crack initiation, and σ_<tp>=σ_a+kσ_m for σ_a>∣σ_m∣, k=0.6〜1.0, or σ_<tp>=(1+k)(σ_a+hσ_m)/(1+h) forσ_m>σ_a>0, where h= 0〜0.5, in the crack propagation process. Then the fatigue damage F_N'=e^<Aσ_t+D>・e^<-γ(N'-1)> where A, D and γ are constants. These constants, which are given as A_i, D_i and γ_i for the crack initiation and A_p, D_p, and γ_p for the crack propagation, can be determined from the fatigue test results. The fatigue tests on annealed low carbon steels under plane bending condition were conducted. The surfaces of the test pieces were observed occasionally with an optical microscope and by the replica method, and the micro-cracks were detected. The fatigue tests under varying mean stresses in stops were also conducted. Those test results were analysed by means of the method mentioned above, and the estimated values had a good agreement with the test results. It was also clarified that the fatigue damage is affected by the stress waveforms and their repeating speeds.
社団法人日本材料学会の論文
1973-08-15

疲労過程を考慮した場合の実働荷重疲労強度の推定

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