| Budget Amount *help |
¥9,200,000 (Direct Cost: ¥8,300,000、Indirect Cost: ¥900,000)
Fiscal Year 2007: ¥3,900,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥900,000)
Fiscal Year 2006: ¥5,300,000 (Direct Cost: ¥5,300,000)
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| Research Abstract |
In order to assess the extremely low cycle fatigue strength of welded joints, the strain at weld toe where cracks usually initiates (local strain), should be estimated. For obtaining the local strain by FEA, the use of very fine elements is inevitable to simulate the accurate weld toe shape. It is not practical, however, to use fine mesh in engineering practice. Therefore in this study, the correlation between the load strain at the weld toe and the nominal strain of the member, which can be obtained by beam model conventionally used in design phase, was established. Namely, the strain ranges computed with fine mesh model taking into account the weld toe profile were correlated to the strains obtained with the 1mm mesh size model, which does not model the weld toe profile. The strain by three-dimensional FE analysis with 1mm mesh size model was correlated with the strain by beam element model. Based on these results, the relationship between the kcal strain range and the nominal strain range was established. Finally, the extremely low cycle fatigue assessment method based on the nominal strain was proposed. In the method, the nominal strain obtained by beam analysis can be converted to the local stain with the established correlation. Then, the extremely low cycle fatigue life can be evaluated by using the proposed fatigue strength curves and Miner's linear cumulative damage rule. In order to vat the proposed assessment method, steel pier specimens were fabricated and subjected to large cyclic deformations. After the test, it was indicated that correlation between the test results and the lives estimated by proposed approach was good enough, and the proposed assessment method can be used to predict the fatigue life of the pier
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