溶接継手の疲労寿命に及ぼす荷重履歴の影響

概要

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There are some ships of which stress states at fatigue crack initiation spots are affected by cargo loading conditions. For example, at a bilge knuckle part of a double hull tanker, the mean stress is tensile on a full load condition while compressive in ballast. In this paper, the fatigue crack initiation life in weldment under the wave induced cyclic loading with the change of mean stress due to the cargo loading condition was studied based on the following fatigue test results. ·Fatigue test with the applied (nominal) minimum stress set to zero. ·Fatigue test with the applied (nominal) maximum stress set to zero. ·Fatigue test applying two loading blocks alternately. The applied (nominal) maximum stress of a loading block was set to 170 MPa, and the minimum stress of the other block was set to -170 MPa. The effect of load history on the fatigue crack initiation life of a welded joint was discussed, and the followings were obtained as the main conclusions. (1) In the compressive loading block following the tensile loading block, the fatigue damage is very small and negligible. (2) The effect of the loading history above-mentioned can be well explained using the equivalent stress, in which the change of the residual stress at the crack initiation spot is taken into consideration.
社団法人日本船舶海洋工学会の論文