厚肉球状黒鉛鋳鉄の動的破壊靱性とその評価

概要

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The objective of this study is to characterize the behavior of dynamic fracture toughness of a thick-walled ferritic spheroidal graphite iron and to evaluate this material for unstable fracture. Unlike static elastic-plastic fracture toughness J_<IC>, the distribution of graphite nodule has a very slight effect on the upper shelf dynamic elastic-plastic fracture toughness J_<Id>. Upper shelf fracture toughness increases with increase in stress intensity rate K. This increase in fracture toughness is mainly attributed to increase in strength at high rate of K. Ductile-brittle transition temperature is linearly related to the logarithm of K. In the upper shelf region, converted plane strain fracture toughness divided by yield strength can be adopted as a material constant that is independent of K and temperature. On the basis of the J_<IC>-temperature curve and the results of impact bending tests on small size specimens, it can be made to estimate the behavior of J_<Id> as for temperature and the predetermined K. In the upper shelf region of the material investigated, the maximum allowable surface flaw depth exceeds the minimum detectable flaw size by a nondestructive inspection. Ferritic spheroidal graphite iron can be used as a material for casks in the upper shelf region at least.
1994-04-01