SNCM8 鋼の組合せ荷重疲れ試験下におけるき裂の発生と伝ぱ(<特集>鉄鋼材料の破壊靱性)

概要

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The behavior of initiation and propagation of cracks on quench-tempered SNCM8 steel fatigued under combined axial loading and torsion was investigated in particular relation to the inhomogeneity of metallurgical structure. The main conclusions are as follows : (1) An inhomogeneous structure was produced in the steel as a result of segregation of manganese and the lower hardness constituents as τ_a/σ_a-ratio became higher, where τ_a and σ_a were shear stress and axial stress amplitudes, respectively. (3) The threshold amplitude of stress intensity for Mode I crack, K_<Iath>, was 5.07 MPa√<m> and that for Mode II crack, K_<IIath>, was 12.4 MPa√<m>. (4) When τ_a/σ_a≤1/√<3>, the specimens were fractured by the preferential propagation of Mode I crack originating from non-metalic inclusions. The critical length of Mode I propagating crack at the fatigue limit was observed to be about 0.1 mm. This agreed with an estimation by using the K_<Iath> value. When τ_a/σ_a≥√<3>, the fatigue limit corresponded to the critical stress amplitude below which plastic strain amplitude was hardly detectable macroscopically.
社団法人日本鉄鋼協会の論文
1978-06-01