定荷重負荷を受ける切欠き材の延性き裂成長と不安定破壊遷移限界

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Considerations have been conducted of fracture transition behaviors of notched specimen extracted from 7 kinds of structural steels under dead loading. Three point bending COD specimens and center-notched tensile specimens are prepared for both monotonic loading and dead loading tests. The load-controlled testing machine is newly developed. Fibrous crack extention initiates at a certain critical COD, δ_i which should be a material constant regardless of testing machines. Although no crack growth is observed by dead loading below δ_i, a certain value of increment of crack growth under constant load beyond δ_i-level can be observed. The reason of crack growth under dead loading can be explained by CTOD(CTOA)-behaviors observed in the vicinity of the growing fibrous crack by using scanning electron microscope. At any δ-value above the critical COD level, (δ_u)_d or (δ_m)_d, the crack growth increase is not limited and instability immediately occurs in brittle manner at low temperature or in ductile manner at relatively higher temperature. The critical COD, (_u)_d or (_m)_d is considerably smaller than _u or _m obtained by monotonic loading test. In particular, (_u)_d is equal to or a little higher than _i. The above results can be observed regardless of kind of steel and of loading mode. Moreover, (_u)_d-value obtained by bending COD test of deeply notched specimen is almostly equal to that by dead loading tensile test of deeply center-notched specimen. It can be clarified by bending COD test with extremely low strain rate that the critical COD is independent of strain rate, although the maximum bending load value is affected by strain rate.
社団法人日本船舶海洋工学会の論文

定荷重負荷を受ける切欠き材の延性き裂成長と不安定破壊遷移限界

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