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In order to study the probabilistic characteristics of the initiation and propagation of cracks, rotating bending fatigue tests of heat-treated 0.45 % C steel smooth specimens were carried out in three stress ranges (1.1σ_w < σ_a < 1.6σ_w,σ_w : fatigue limit). The 16 specimens were tested at each stress range. The following results were obtained through the successive observations of cracks which led to final fracture. The propagation life of a crack from initiation up to fracture, N_<i-f>, and the total number of cycles to fracture, N_f, are expressed by the three-parameter Weibull distribution. A slight dependency of the coefficient of variation, CV, in N_<i-f> on the stress range is recognized. Although the initiation life of a crack, N_i, is also expressed by the three-parameter Weibull distribution, the value of CV increases with the decrease in stress range.
In order to study the probabilistic characteristics of the initiation and propagation of cracks, rotating bending fatigue tests of heat-treated 0.45 % C steel smooth specimens were carried out in three stress ranges (1.1σ_w < σ_a < 1.6σ_w,σ_w : fatigue limit). The 16 specimens were tested at each stress range. The following results were obtained through the successive observations of cracks which led to final fracture. The propagation life of a crack from initiation up to fracture, N_<i-f>, and the total number of cycles to fracture, N_f, are expressed by the three-parameter Weibull distribution. A slight dependency of the coefficient of variation, CV, in N_<i-f> on the stress range is recognized. Although the initiation life of a crack, N_i, is also expressed by the three-parameter Weibull distribution, the value of CV increases with the decrease in stress range.
