不安定破壊開始条件としてのJ_c-δ_c基準と破壊靱性評価手法

概要

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Study has been carried out to clarify the applicable range of COD and J_c-criteria which have been proposed as useful criteria in the fracture of non-linear charactristic materials. At first, evaluation methods of COD and J- integral and the applicable range of these methods were made clear; in particular, simplified formulas for estimating J-integral of a shallow notched specimen were newly established. Both COD- and J- values estimated by a proper procedure dominate the distribution of the equivalent plastic strain in the vicinity of the blunting tip of a notch; however, they can no longer control the nominal stress al which is related to the initiation of cleavage crack. Therefore, the critical δ_c- and J_c- values depend essentially upon the plastic constraint in the vicinity of notch tip. J_c-δ_c criterion has been newly proposed as a useful criterion for unstable brittle fracture. Using J_c-δ_c criterion, it could be expected that fracture toughness testing for estimating plane strain fracture toughness becomes more easy.
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