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摘要
A unified classical maximum likelihood approach for estimating P-S-N curves of the three commonly used fatigue stress-life relations, namely three parameter, Langer and Basquin, is presented by extrapolating the classical maximum likelihood method to the Langer relation. This approach is applied to deal with the S-N data obtained from a so-called maximum likelihood method-fatigue test. In the test, a group of specimens are tested at a so-called reference load, which is specially taken care of by practice, and residual specimens are individually fatigued at different loads. The approach takes a basis of the local statistical parameters of the logarithms of fatigue lives at the reference load. According to an assumption that the material constants in each relation are concurrently in same probabilistic level, the curves is described by a general form of mean and standard deviation curves of the logarithm of fatigue life, in which four material constants are at most contained. The constants in the curves are estimated by a mathematical programming method to be in agreement with the maximum likelihood principle. Availability of the approach has been indicated by an analysis of the S-N data of 45# carbon stell-notched specimens (kt = 2.0) subjected to fully reversed axial loads. The analysis reveals that an appropriate relation should be determined by comparing the fit, the fitted error and the safety in practice, of the three relations. The fit is best for three-parameter relation, slightly inferior for the Langer one and poor for the Basquin. Considering the fitted error and the safety in practice, the Basquin one is not an appropriate relation for the data. In addition, classical maximum likelihood method-based predictions might be affected by the local statistical characteristics of test data at the reference load to be non-conservatively. To avoid the affects, an improved method, which could reduce the affects to a maximum, should be worthily explored.
- 出版日期2001
