残留応力を有する部材の脆性破壊強度評価へのローカルアプローチの適用 : 予荷重による圧縮残留応力の影響の評価

概要

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In this study, an effect of residual stresses on brittle fracture initiation for a structural steel is investigated on the basis of the Local Approach. Compressive residual stress is introduced by pre-loading at a room temperature and the subsequent fracture test is conducted at low temperatures ( - 75℃ and -40℃) with a high strength steel of 780 MPa class. It is shown that the pre-loading apparently elevates the critical load and critical CTOD at the onset of brittle fracture initiation. This is explained in terms of the effect of a compressive stress field near the crack tip. This paper employs the Weibull stress fracture criterion to evaluate the brittle fracture resistance of the pre-loaded specimen. The assertion is that the critical Weibull stress at brittle fracture initiation is a material property independent of test conditions with and without pre-loading. Using the Weibull stress fracture criterion, the critical CTOD of the pre-loaded specimen can be predicted from fracture test results of the specimen without pre-loading.