混合モード状態における脆性破壊発生に関する考察

概要

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Several criteria to predict fracture initiation from cracks subjected to combined modes of loading are discussed. In conjunction with the discussion, a strip yield model for an elasto-plastic crack under combined modes of loading is proposed, which is an extension of the model for single mode of loading developed by D.S. Dugdale and B.A. Bilby et al. Experimental work was also performed to investigate the brittle fracture initiation under combined mode I and II or mode I and III. Tension and bend tests were carried out at low temperature using mild steel and 80 kg/mm^2 class high tensile steel. Notches in the specimen are introduced in planes inclined to that of principal stress to give a required state of stress in the vicinity of the crack tip. The results of these tests and those by other researchers were analysed using various criteria proposed hitherto. It was observed that the small scale yielding fracture under combined modes of loading can be predicted reasonably well using the maximum hoop stress criterion or the crack opening displacement criterion based on the proposed model. For practical application of the proposed model, further investigation is need as how to define the stress condition within the yielded zone and also the crack opening displacement.
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