A Study on Brittle Fracture Initiation from Inclined Cracks

概要

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Several criteria to predict fracture initiation from cracks subjected to a combined mode loading were discussed. In conjunction with the discussion, a generalized strip yield model for an elasto-plastic crack under a combined mode loading was proposed, which is an extension of the model for a single mode loading developed by D.S. Dugdale and B.A. Bilby et al. The validity of this proposed model for evaluation of COD under a combined Mode I and II loading was verified through the measurement of COD using Moire method. Experimental work was also performed to investigate the brittle fracture initiation under the combined Mode I and II loading. Tension fracture tests were carried out at low temperatures using specimens with an inclined notch. The material used for testing was SM41A mild steel. The results of these tests and those by other researchers were analysed using various criteria. It was found that the fracture strength under the combined Mode I and II loading can be predicted reasonably well using the crack opening displacement criterion based on the proposed model. For fracture under small scale yielding conditions, the maximum hoop stress criterion also gives a good representation of the results. The fracture evaluation of structural members with inclined flaws using these criteria is in good agreement with the method adopted in the ASME B & PV Code Section XI.
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