Direct damage evaluation method for thermal fatigue based on power spectrum density functions

Sakai, Shinsuke*; Honda, Kei*; Okajima, Satoshi*; Izumi, Satoshi*; Kasahara, Naoto

At an incomplete mixing area of high and low temperature fluids, fluid temperature fluctuation often occurs. It induces cyclic thermal stresses in the wall, which may result in fatigue crack initiation. Kasahara et al. proposed the thermal fatigue evaluation method based on power spectrum density (PSD). This method generalizes the evaluation procedure by preparing PSD charts of fluid and frequency transfer functions of stress for various kinds of plant components. From design point of view, however, this method is too complicated due to the inverse Fourier transform and wave decomposition procedures named Rain Flow Cycle Counting (RFC). In this paper, simplified damage evaluation method for thermal fatigue is proposed by directly evaluating fatigue damage from PSD of stress.