Influence of residual stress relief on fatigue crack growth rate in welding residual stress field.

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  • 溶接残留応力場での疲労き裂成長速度に及ぼす残留応力緩和の影響
  • ヨウセツ ザンリュウ オウリョクバ デ ノ ヒロウ キレツ セイチョウ ソクド

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It is well known that the welded residual stress has marked influence on fatigue crack growth rate in welding structure. In particular, because the tensile residual stress may accelerate the fatigue crack growth rate, it is important to develope the method of residual stress-relief. We have succeeded in relief of residual stress up to about 80% by using a method of mechanical stress relief which was the slow preloading of welded joint. The effects of residual stress relieved, stress ratio and preloadingg on fatigue crack growth rate in welded joints were investigated in associated with crack closure phenomenon. The results obtained are summarized as follows.<br>(1) For the tensile residual stress fields after preloading, the fatigue crack growth rate was accelerated by the tensile residual stress relieved even if the stress ratio was low. Then, the fatigue crack growth rate accelerated was not changed regardless of the strength of residual stress fields and stress ratio.<br>(2) For the compressive residual stress fields after preloading, the fatigue crack growth rate was considerably lower than that of base metal. After the crack arrested as the stress intensity range approached the threshold for crack growth, the fatigue crack growth rate increased with increasing stress intensity range and stress ratio.<br>(3) The preloading scarecely resulted in the change of crack growth rate in the tensile residual stress field but markedly accelerated the rate in the compressive residual stress field.<br>(4) It became clear that the effects of welding residual stress, stress ratio and preloading on fatigue crack growth rate in welding residual stress fields can be explained by the effective stress intensity range defined from both the welding residual stress- and plastic- induced crack closure.

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