Creep-Rupture Reliability Analysis

A probablistic approach to the correlation and extrapolation of creep–rupture data is presented. Time–temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson–Miller and on the Manson–Haferd parameters, but it can be applied to any of the TTP’s. A method is developed for evaluating material dependent constants for TTP’s. It is shown that “optimized” constants can provide a significant improvement in the correlation of the data, thereby reducing modeling error. Attempts were made to quantify the performance of the proposed method in predicting long-term behavior. Bias and uncertainty in predicting long-term behavior from short-term tests were derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state-of-the-art reliability methods to the design of components under creep.