小口径配管ソケット溶接継手の疲労特性 : 破壊力学的検討と寿命評価マップの作成

概要

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The fatigue properties of socket-weld-jointed pipes have not yet been investigated in detail. The fatigue limit and failure mode of socket-weld-jointed pipe specimens were revealed in a previous study. To extrapolate the very long fatigue lives which cannot be obtained experimentally, we analyzed the fatigue lives of socket-weld-jointed pipes using fracture mechanics. The results obtained are summarized as follows. (1) In most weld joints, the slit was formed between pipe and socket, and behaved like a crack. The stress intensity factors (K) of these slit like cracks were analyzed using the FEM. This crack is subjected to mixed mode I-II loading. K_θ had a maximum value in a direction at an angle of about 65 degrees to the axial direction. (2) About half of the weld joints had weld defects 0.5〜1.5mm high. This crack is subjected almost to mode I loading. (3) The propagation path angles were predicted to be 65〜85 degrees using the maximum principal stress criterion. This value is in good agreement with the experimental results. (4) The fatigue crack propagation lives were calculated using the da/dN-ΔK relation. The S-N diagram theoretically was compared with the test results. They were in good agreement. (5) For pipe maintenance, a map that could be used to evaluate the fatigue life from the stress and weld defect size was constructed.
社団法人日本機械学会の論文
1998-02-25