New advances of the strain-based fatigue reliability theory and methods

作者：Zhao Yongxiang; Yang Bing; Zhang Weihua

来源：Journal of Mechanical Strength, 2005, 27(5): 604-611.

New advances are introduced in fatigue test method, assessment curves, and fatigue damage mechanism dealing the strain-based fatigue reliability theories and methods. From saving cost, a so-called general maximum likelihood test method is newly presented with a few of specimens to obtain the data for assessing the material random fatigue properties. The random cyclic stress-strain responses are found and its probabilistic model is established. At the same time, a new probabilistic model of random cyclic strain-life relations is also developed. These probabilistic models should be appropriately estimated by a so-called general maximum likelihood method in which both probabilistic effects of the scattered regularities of test data and the sampling size are taken into account on a sense of entire test data. From considerations of the random stress-strain relations deriving into a random cyclic strain load and the random strain-life relations reflecting the material cyclic strain strength, a cyclic strain load-strength interference model is derived to perform the reliability analysis under a constant cyclic straining. Combining the Kecocioglu s recurrence formula, the reliability analysis under conditions of variable cyclic strain amplitudes and spectrum can be made. These indicate that a new systematic reliability theory has been established. Further, a so-called effectively short fatigue crack criterion is applied to represent the fatigue damage mechanism. It is revealed that the intrinsic cause of random fatigue properties is the difference of the microstructural conditions in the initial zone and then the zones ahead of the dominant effectively fatigue crack, which result in the specimen failure. The three random relations of fatigue crack growth rates, cyclic stress/strain-lives, and cyclic stress-strains are relatively random relations. The fatigue damage is involving a process involving from an initial chaotic state, to an independent random state, and then to historically related random state.

• 出版日期2005