Abstract
Abstract In fracture toughness testing of welds, weld residual stress often makes it difficult to obtain a straight precrack front. Therefore, BS 7448-2, Fracture Mechanics Toughness Tests. Method for Determination of KIc, Critical CTOD and Critical J Values of Welds in Metallic Materials, and ISO 15653, Metallic Materials – Method of Test for the Determination of Quasistatic Fracture Toughness of Welds, recommend techniques for modifying weld residual stress to achieve a straight precrack front. BS 7448-2 prescribes three techniques: local compression, reverse bending, and a stepwise high stress ratio (R-ratio) technique. However, in ISO 15653, which was newly published in 2010, the reverse bending technique was rejected because detailed conditions for obtaining a reliable effect were not provided. In the revision of ISO 15653 in 2018, the reverse bending technique was revived with a proposal of appropriate conditions. The present paper reviews the conditions of reverse bending proposed in the revision of ISO 15653, together with the technical background. The effectiveness of the proposed reverse bending conditions is demonstrated experimentally by precracking in weld specimens with a thickness of 127 mm (5 inches). The effects of the two other techniques, i.e., the local compression and stepwise high R-ratio techniques, are also examined, and the effects of each technique on crack front straightness and the required fatigue cycles to finalize precracking are discussed.
Published Version
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