Failure mechanism of a thermocouple well caused by flow-induced vibration (2) interaction between flow-induced vibration and fatigue crack growth in a thermocouple well

摘要

In the preceding paper a simplified master diagram on the relationship between a reduced velocity Vr(=V/fD) and a reduced displacement amplitude y/D is investigated for the in-line oscillation mode of thermocouple well. Based on this diagram, high cycle fatigue failure process of a thermocouple well; crack initiation, crack growth/arrest, and final stage of fracture, is evaluated in this paper.The strain amplitude at the root between thin and thick well tubes can be analytically estimated considering the sharp notch effect, and the crack initiation life can be evaluated using a fatigue curve. After short crack growth the crack front line canmove as a long crack. Both of natural frequency and damping constant are changed, and crack growth reduces the displacement amplitude. As the results crack arrest and delayed failure, which are peculiar in flow-induced vibration, can occur in athermometer.