続. 低温環境中における繰返し荷重下の鋼材の安全性評価

概要

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Fracture toughness tests and fatigue tests on welds of steels (ship structural steel and pressure vessel steel) were carried out in order to investigate the mechanisms and factors to govern the brittle fracture initiation during the fatigue crack propagation at low temperatures. The welding residual stress was released and its distribution was altered according to the fatigue crack propagation. Although, if the effect of the residual stress was taken into consideration, the fatigue fracture toughness K_<fc> was estimated as equivalent as the monotonic loading fracture toughness K_c which were obtained under the same loading rate(K^^・=dK/dt). Thus, the fatigue fracture toughness can be obtained from the monotonic loading fracture toughness if it were known as a function of the loading rate and the distribution of released residual stress were also as a function of the crack length. The safety assessment of a large component in a structure will be also estimated from the knowledge of the monotonic loading fracture toughness under given service conditions (temperature and loading rate), since the alternation of residual stress may be negligible in a large welded component due to the fatigue crack propagation.
社団法人日本船舶海洋工学会の論文