溶接残留応力場におけるき裂伝播経路の数値予測とぜい性破壊挙動に関する考察

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It is well known that welding lines are the critical parts of structures in relation to the initiation and propagation of brittle fracture. The evaluation of fracture toughness of weldment is usually performed by applying conventional fracture mechanics. This ap-proach, however, faces difficulty, when fracture near the welding line form unstably curved crack paths due to the welding residual stresses and material inhomogeneities. In the present paper the computational crack path prediction, which has been proposed by the present authors, is applied to understand the fracture behavior near the weldment. For this purpose the computer code is modified to include the procedure of releasing the welding residual stresses with increasing crack length. The step-by-step stress analyses are carried out in order to advance the crack tip along the appropriate path, where a first order perturbation solution of a curved crack is combined with the fracture path criterion of local symmetry. Since material inhomogeneity along the welding line is disregarded in the present analysis, fracture paths are affected only by the distribution of welding residual stresses. Numerical simulations are performed for various types of fracture in weldments. In case of a brittle crack normally intersecting a welding line, a straight crack extension is initially expected under the influence of tensile residual stress parallel to the welding line. When the crack extends further into the compressive residual stress field, it sometimes changes its direction parallel to the welding line resulting its arrest due to the rapid decrease of K_I. In case of a crack approaching a welding line with a small acute angle, the compressive residual stress causes crack branching being parallel to the welding line, and the crack may not intersect the welding line. These numerical results are in extremely good agreement with actual crack paths observed in brittle fracture experiments. Investigations are also made for the brittle fracture propagating along the welding line. The results of the numerical simulations show that if the magnitude of the applied tensile stress acting normal to the initial crack direction is small compared with that of the welding residual stress, the brittle crack may form curved extension and propagate from the welding line to the base metal.
社団法人日本船舶海洋工学会の論文

溶接残留応力場におけるき裂伝播経路の数値予測とぜい性破壊挙動に関する考察

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