Reverse bend experiments on the base plate and discussion of the appropriate amount of reverse bending for precrack straightness (Effect of the reverse bend process on the CTOD toughness evaluation and understanding of its mechanisms)

Tomoya Kawabata; Hoichi Kitano; Takumi Ozawa; Yoshiki Mikami

doi:10.1016/j.tafmec.2025.104869

論文 Reverse bend experiments on the base plate and discussion of the appropriate amount of reverse bending for precrack straightness (Effect of the reverse bend process on the CTOD toughness evaluation and understanding of its mechanisms)

Tomoya Kawabata ; Hoichi Kitano (National Institute for Materials Science) ; Takumi Ozawa ; Yoshiki Mikami

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Tomoya Kawabata, Hoichi Kitano, Takumi Ozawa, Yoshiki Mikami. Reverse bend experiments on the base plate and discussion of the appropriate amount of reverse bending for precrack straightness (Effect of the reverse bend process on the CTOD toughness evaluation and understanding of its mechanisms). Theoretical and Applied Fracture Mechanics. 2025, 137 (), 104869.

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(abstract)

Measurements of the critical value of the crack-tip opening displacement (CTOD) of welded joints often suffer from weld residual stresses, which prevent the introduction of a straight precrack front. In this study, the effects of reverse bending, a proven method for straightening the crack front shape, on evaluations of the critical CTOD are investigated. To compare the differences in the evaluation results, the authors used a base plate without residual stress inside the material for their experiments. Five different reverse bending treatments were applied to a 50 mm thick base metal, and the effects of reverse bending were evaluated via CTOD tests at low temperatures. Additionally, numerical simulations were carried out via the finite element method to exclude the effects of a0/W and af, which cannot be unified in the experiments, and to understand the mechanism. After reverse bending and unloading, the tensile residual stress is distributed at the notch edge, and a high stress intensity at the fatigue crack tip during CTOD testing can be expected. In addition, when the amount of reverse bending is increased to Lr = 1.35, the compressive residual stress distribution in front of the specimen expands, and the P–Vg curve clearly decreases, which may impair the precrack shape flatness. Therefore, the controlled range of Lr should be at least less than 1.35.

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