| Summary: | 碩士 === 國立成功大學 === 土木工程學系碩博士班 === 95 === This study is to determine the mixed mode stress intensity factors (SIFs), KI and KII, of load-carrying fillet welded cruciform joints numerically and experimentally by Least-Squares Method, and the SIF results were normalized to magnification factors showing how the geometric dimensional parameters of the fillet welded cruciform joints affect SIFs. In numerical part of the study, numerous numerical examples of various geometric dimensional parameters were analyzed and the SIF results were employed to develop the regression formulas of KI and KII for the cruciform joints. In experimental part of this study, a total of fifteen cruciform joint specimens were tested and analyzed in the digital-camera experiment. The test results showed that the proposed experimental method was able to give satisfactory SIF evaluation for the load-carrying fillet welded cruciform joints, and verified the SIF formula for cruciform joints adopted in British Standard PD-6493 and results of numerical simulation at the same time.
In summary, numerical and experimental results show that the decreasing crack length in the un-penetrated area of a cruciform joint leads to the decreasing KI and KII values for the crack tip, and the decreasing fillet weld leg size for the cruciform joints generates the higher KI value. In fact, the experimental method presented can be applied to determine the SIF of any detail with surface crack where the Irwin’s series solution for crack-tip displacement fields is valid. Due to its simplicity and portability, the experimental method presented is applicable to field measurement of SIFs directly from a detail of interest at the site, which is very useful for fatigue evaluation of details in structures like steel bridges or offshore structures.
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