溶接によりき裂部近傍がうける熱ひずみ履歴と残留応力・残留ひずみ

概要

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In the welded joint having a pre-existing defect, the crack tip is subjected to thermal-strain and stress cycles by successive welding. Hot straining embrittlement and residual stress due to successive welding will influence the brittle fracture initiation of weldment. Two-dimensional finite element method analyse are carried out for obtaining therm*^1 stress-strain cycles during welding and distribution of residual stresses-strains near the tip of a pre-existing crack. Appreciable difference in residual stress distribution is not observed between Before-Weld-Notch (BWN) and After-Weld-Notch (AWN) specimens. Much difference in the residual equivalent plastic strain is observed between BWN and AWN specimen. In BWN-specimen, there is a large concentration of plastic strain near crack tip during welding. This hot-straining causes considerable decrease in fracture toughness. In the welded joint of steel, the residual stress-strain distributions near crack tip is decided by the parameter T^c_<max/>/σ_<Y0> where T^c_<max> is the maximum heating temperature at the crack tip and _<Y0> is the yield stress of materials at room temperature. The conventional formulae on residual stress distribution and residual equivalent plastic strain in the vicinity of a pre-existing crack are shown using the parameter T^c_<max>/_<Y0>.
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