球状黒鉛鋳鉄の切欠き付CT試験片の破壊じん性

概要

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The fracture toughness tests of ductile cast iron (JIS FCD 60) were conducted at room temperature by using compact tension specimens with blunt-notches. The method to determine the point of crack extension was established and the effect of notch-tip radius on the fracture toughness K_i was investigated. The main results obtained are summarized as follows: (1) The DC electrical potential method can be applied to detect the point of crack extension in blunt-notched CT specimens of ductile cast iron, which is almost identical to that determined by the R-curve method. Acoustic emissions became severe before the crack extension point was detected by the electrical potential method. (2) The relation between K_i and notch-tip radius ρ can be divided into three regions: region I where ρ is smaller than the radius of spheroidal graphite ρ_G(30μm), region II where ρ is above ρ_G and below 2mm, and region III where ρ is larger than 2mm. K_i was constant in regions I and III, while it increased linearly with √ρ in region II. The plastic strain ε_f on the fracture surface estimated by X-rays showed a similar trend in its variation with ρ. In region II, ε_f became larger with increasing (K_i)/√<ρσ_Y>.
社団法人日本材料学会の論文
1983-12-15