遷移温度域の弾塑性破壊じん性に及ぼすひずみ速度の影響(破壊力学特集)

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Static and dynamic fracture toughness tests at three strain rates were performed on two ASTM A508Cl. 3 steels by using 1T-CT specimens and fatigue pre-cracked instrumented Charpy specimens. The K_<JC> converted from J_C of the small specimens indicated a wide scatter. When the strain rate increased, the fracture toughness transition curves shifted to a higher temperature region. An increase in strain rate reduced the scatter of K_<JC> dramatically, especially in the high temperature region, and decreased the lower bound fracture toughness. Fractographic examination of the fractured specimen surfaces indicated that the relationships between K_<JC> and the stable crack growth, Δα_0, distance from stable crack front to trigger point, X, or distance from fatigue crack front to trigger point, Δα_0+X, were expressible by a single curve, respectively. The scatter of K_<JC> was caused by the varience of Δα_0, X, and Δα_0+X. With increasing strain rate, Δa_0, X, and Δα_0+X decreased significantly, leading to a small scatter of K_<JC>. The K_<JC> value at Δα_0, X=0, and Δα_0+X=0 was proposed as the lower bound fracture toughness of a steel and labeled K_<JCi>. The shape of K_<JCi> versus temperature curve was controlled by the critical stretch zone width, SZWc. The Weibull slope m of K_<JC> became larger with increasing strain rate and decreasing temperature. Higher toughness data with larger stable crack extension than 100μm violated the linearity of Weibull plots. In the statistical approach to determine the lower bound fracture toughness in the transition region, much analytical development is needed. The K_<JC> value with 3% fracture probability coincided with the K_<JCi> value in the low temperature region even in a high strain rate.
社団法人日本材料学会の論文
1994-10-15

遷移温度域の弾塑性破壊じん性に及ぼすひずみ速度の影響(破壊力学特集)

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