高張力鋼の切欠きCT試験片の破壊じん性試験破面のX線的研究

概要

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Fracture toughness tests were carried out with blunt notched compact tension specimens of a high-strength low alloy steel, JIS SNCM 8 (equivalent to AISI 4340), tempered at several temperatures. The stress intensity factor K_ρ at the initiation of crack extension detected by the DC potential method was related to the initial notch-tip radius ρ by K_ρ=K_0(1+ρ/ρ_0)^<1/2> where K_0 and ρ_0 are material constants. This was derived through the concept of the fictitious notch-tip radius proposed by Tanaka and Hirose. The values of material constants K_0 and ρ_0 took the lowest values for the material tempered at 300℃. The residual stress near the fracture surface measured by the X-ray diffraction technique was tension. The depth of the plastic zone ω_y was measured by the distribution of residual stress beneath the fracture surface. It was related to the stress intensity factor at crack initiation K_i by the following fracture mechanics equation : ω_y=α(K_i/σ_Y)^2 where σ_y is the yield stress and α is from 0.14 to 0.12. The values of residual stresses very close to the fracture surface tended to decrease with increasing K_i, and were found to be a single-valued function of the fracture strain at the notch-tip determined from K_0 and ρ_0 values based on the fictitious notch-tip radius concept.
社団法人日本材料学会の論文
1983-07-15