Abstract
In order to assess the thermal fatigue caused by the local temperature fluctuation, it is important to evaluate the stress gradient in the thickness direction in addition to the stress on the surface. In this study, the stress distribution in the depth direction was investigated for various constraint conditions in order to predict the crack initiation and growth behaviors. Not only a sinusoidal but also a trapezoidal fluid temperature fluctuation was analyzed. It was shown that the stress range on the surface caused by the trapezoidal fluid temperature fluctuation could be more than aEΔT/(1-v) for low frequency condition without the membrane constraint, and it could be 2 aEΔT/(1-v) at the maximum. The SIF was derived by the weight function method using the evaluated stress distribution. It was shown that, even under the thermal stress fluctuation, the crack can penetrates the wall thickness without the threshold SIF ΔK_<th> for crack arrest. If the ΔK_<th> was considered, the crack may stop growing under a sinusoidal fluid temperature fluctuation without the membrane constraint. The reason for the arrest of crack growth at the mixing tee and the crack penetration at the branched elbow was reasonably explained from the analyzed results.
