溶接継手部の疲労き裂伝播シミュレーション解析
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概要
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Recently, the fatigue design taking stress concentration due to welding bead into account have been applied to LNG carriers and offshore structures. In case of adopting this design criteria, the deviation of stress concentration factor at weld toe plays an important role. And the deviation of this stress concentration factor is usually larger than that of fatigue fracture life. This is because that fatigue crack propagation life does not largely deviate by the irregularity of stress concentration factor due to welding bead. Generally, on the fracture mechanics approach for fatigue crack propagation, a simple calculation model of stress intensity factor is used, and the fatigue strength is calculated by deterministic approach. The approach of this paper is as follows; Applying of probabilistic approach (Monte Carlo method) for fracture mechanics, the fatigue crack propagation behavior of multi-cracks under irregular stress field of welded joints is numerically simulated. Using this developed computer simulating system, the fatigue tests of welded joints can be numerically carried out. As the results of numerical fatigue tests for non-load-carrying fillet welded joints of aluminum alloy. 5083-O, the following conclusions are obtained. a) The fatigue lives by numerical analysis are in approximate agreement with experimental data. In this analysis, the practical statistical parameters from measured weld bead shape data to calculate stress concentration factor, the available experimental data of fatigue crack initiation life for smooth specimens and available material constants are used. b) Though the calculated deviation of fatigue crack initiation life is comparatively large, the standard deviations of fatigue fracture life are small as 0.064-0.101. These values are almost same as experimental data of 0.07. c) Comparing to conventional fatigue crack propagation approach with assumption of calculating model of single crack under uniform stress field, this approach can reasonably simulate the fatigue behavior of multi-cracks at each stage of crack initiation, crack propagation and crack coalescence. The fatigue crack coalescence make fatigue crack propagation life shorten.
- 社団法人日本船舶海洋工学会の論文
- 1985-08-24
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