切欠き試験片の S-N 曲線の多数収集データの整理検討について

概要

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In the previous paper, the fatigue strength data of notched specimens of steels had been analyzed by distenguishing the fatigue limit for crack initiation σ_<w1>, and that for fracture, σ_<w2>, with the aid of Nishitani's critical notch radius ρ_0, at the branch point, i.e., at the critical point where a non-propagating crack appears. In this study, S-N (P-N, S-T) data of rotary bending tests of sharp (notch radius ρ ≃ρ_0), deep (notch depth t≫√<ρt>/5), notched specimens of steels were extracted from JSMS Data Book and analyzed by fitting a bi-linear type S-N curve coprising of inclined and horizontal straight lines on a Log-Log diagram, using Nishijima's method. By taking the stress intensity factor K of the circumferential crack with notch depth t instead of the stress σ in S-N curves, and by using the following correction factor χ for low strength steels, i. e. κ=σ_B/σ_C for tensile strength σ_B<σ_C=940MPa, κ=1 for σ_B≧σ_C, S-N Data of sharp, deep notched specimens of both low and high stength steels could be fitted by a bi-linear type curve on a Log (K/κ)-Lot N diagram (Fig. 4(e)), with the coefficient of variation, 14.0%, while the coefficient of variation for the Log (σ/σ_B)-Log N diagram (Fig. 3(c)) of corresponding smooth specimens was 11.8%.
社団法人日本材料学会の論文
1989-10-15