切欠部からの破壊発生に関するCOD-クライテリオンとストレッチド・ゾーン

概要

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The behavior of the stretched zone and fracture initiation at the notch root with increase of the applied load has been investigated at various temperatures. The stretched zone width is almost constant regardless of test temperatures when crack initiates by fibrous crack, while, in the case of cleavage initiation, it takes various values between the above-mentioned value and zero depending on temperature and plastic constraint. When fracture occurs with plastic COD, the critical COD at fracture is reduced by the amount of stretched zone given by the preloading, while the effect of preloading on the critical COD is small when the COD mainly consists of elastic deformation. The process of fracture initiation from the tip of 45°crack has also been investigated and it is found that the stretched zone width of 45°crack specimen is about the same as that in mode I.