減肉を有するエルボ配管の低サイクル疲労強度に関する考究

概要

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Low cycle fatigue tests and finite element analysis were conducted using 100A elbow specimens made of STPT 410 steel with local wall thinning in order to investigate the influences of local wall thinning on the low cycle fatigue behavior of elbows with internal pressure. Local wall thinning was machined on the inside of the elbow and was prepared at extrados, crown and intrados. The parameters of the wall thinning were same (eroded ratio=0.5, eroded angle=180 degrees and eroded length=100mm) in the all test cases. The elbow specimens were subjected to the prescribed cyclic in-plane bending displacement with constant internal pressure of 0 to 12 MPa. Also, low cycle fatigue tests using sound elbows were carried out for comparison. Low cycle fatigue life of wall thinned elbows was not so different regardless of location of wall thinning. Low cycle fatigue strength of the elbow specimens were beneath the best fit fatigue curve and its reason can be explained by combining the equivalent strain range and cumulated damage theory, considering reduction of ductility under multi-axial stress state.