11. On the Correlation between Charpy Impact Value and Fracture Toughness of Welded Joint with Angular Distortion and Misalignment

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Generally there may be the possibility that brittle fracture would start from a welded joint of steel structures, because of some weld errors such as angular distortion and misalignment, some defects such as weld cracking or fatigue crack, and low toughness of welded fusion line. In order to prevent structures from brittle fracture, it is necessary to have enough knowledge about brittle fracture initiating property of welded fusion line which is superposed some weld errors and defects, and to obtain reasonable requirement of toughness for welded steel structures. In this study, brittle fracture test of so-called large scale tensile specimens with angular distortion, misalignment and surface notch was conducted with 8000 ton and 2000 ton test rigs using welded joints of 25, 50 and 75 mm thick mild steel, 50, 60 and 80 kg/mm^2 tensile strength steels. The surface crack of this type of specimen is exposed under the superimposed condition of tensile stress and bending stress. A general approximate formula of stress intensity factor for such a semi-elliptical surface crack was derived from Irwin's solution and Kobayashi's numerical results. This formula was also proved to explain the results of simple tensile and pure bending tests. Furthermore, the bending stress behavior of the tensile specimen with angular distortion and misalignment was analyzed, and a general solution was obtained for the bending stress under elastic end condition. Using these formulae, the critical stress intensity factor for brittle fracture initiation of such a specimen can be evaluated reasonably. In order to evaluate the brittle fracture characteristics of steel structures with a quality control test, an investigation was done on the relation between the critical stress intensity factor of the large scale test and the absorbed energy of Charpy test. Then, modifying Hagiwara's correlation formula between critical COD and Charpy impact energy, a statistical correlation formula was obtained. As a result, it is possible to assess the welded steel structures against brittle fracture initiation by means of fracture mechanics approach using the result of Charpy test which is one of quality control tests.
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11. On the Correlation between Charpy Impact Value and Fracture Toughness of Welded Joint with Angular Distortion and Misalignment

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