A Remaining Life Prediction Method on the Basis of Micro-Crack Initiation and Growth Behavior under Creep-Fatigue in Plain Specimen of 316 Stainless Steel

Abstract

To assure high-temperature component safety and reliability, a life prediction method has been developed. The method is based on the micro-crack growth rate and the microcrack distribution.
Strain controlled low-cycle fatigue tests were carried out on the plain specimens of SUS 316 at 923K in air and the initiation and growth behavior of surface micro-cracks were observed.
The results obtained are summarized below.
(1) The creep-fatigue life is governed by micro-crack growth.
(2) A linear relationship is observed between the logarithms of main surface crack length and the life ratio, N/N_f, for various strain loading conditions.
(3) The distribution of micro-crack length obeys the Weibull distribution.
Moreover, the maximum crack length in an area larger than the sample area can be estimated with a help of the statistics of extremes. Therefore, the remaining life of high-temperature components may be accurately predicted by measuring the distribution of surface micro-crack length in critical parts.