New Numerical Analysis Method for Creep Lifetime of Gas Turbine Materials by Using the Discrete Cosine Transform

Recently the Discrete Cosine Transform has begun to be used to express coefficients of creep equations using the power law or the exponential law such as Bailey-Norton law and Modified θ Projection. In addition, the Discrete Cosine Transform has begun to be used to express creep equation itself. The author has already found that the Discrete Cosine Transform can express the temperature and stress dependence property of the coefficients of the creep equations at the same time by the two-dimensional Discrete Cosine Transform using 8 × 8 discrete signals. Furthermore, the author has already found that the Discrete Cosine Transform can fit measured creep strain values very well from the primary creep region to the tertiary creep region using 8 discrete signals and it can estimate creep strain values between the measured points by interpolation very well. An amazing point of these results is that the Discrete Cosine Transform can go through all the measured points and the values from the interpolation are quite reasonable. Moreover, the author has already found that the Discrete Cosine Transform can fit 40-year long term creep curve and anomalous high temperature creep curves very well. These results have never been obtained before. In the 40-year long term creep data analysis, the Discrete Cosine Transfrom was able to fit the 40-year creep curve from the primary creep region to the tertiary creep region very well using 41 discrete signals. In the anomalous high temperature creep data anlysis, the Discrete Cosine Transform was able to fit the anomalous creep curves very well using 22 discrete signals even though the curves drew any swell. However we have not known if the Discrete Cosine Transform can predict the long term creep curve by using the short term creep data yet. Therefore as a next stage, the author tried to esimate the long term creep curve from the short term creep data of gasturbine materials by extrapolation using the Discrete Cosine Transform. In ASME 2020 Turbo Expo, the author is planning to report the results of the above research on the prediction of the long term creep curve by using the Discrete Cosine Transfrom. Specifically the author is going to explain the prediction method using the numerical anlysis method by utilizing the Fourier Transform Coefficients and others. By using this method, we can obtain both interpolation values and extrapolation values from the short term creep data. This method will advance the world of the computational anlysis such as FEM and so on.