| It is the main work to predict fatigue life in Damage Tolerance Analysis. Usually the fatigue damage accumulation theory and the fracture theory are used in the fatigue crack initiation life estimation and the fatigue crack propagation life estimation respectively. As the estimated fatigue lives can not interlinked harmoniously, it is inconvenient to calculate the frill fatigue life. Thus, it is an important item in the study of fatigue to develop fatigue full-life estimation methodology which calculates the fatigue crack initiation life and crack propagation life with a uniform theory.Firstly, some analyses of the fatigue crack propagation characteristics and key influence factors are done in this paper. An equation is established which correlates the fatigue crack-closure factor U and the crack propagation parameter C(R). A numerical method is also developed to determine the crack propagation parameter C(R). Based on these work, the crack growth rate equation is establised under spectrum loading conditions, in which the detain factor in the equivalent damage model is introduced. The application of this equation shows that it is efficient to predict fatigue life.Secondly, the initial fatigue integral length is introducd in the stress-intensity factor equation, then the stress-intensity factor range t~K is used as the crack propagation parameter. A small crack growth rate equation is established refering to the small crack closure size-effect. The study of the initial fatigue integral length shows that it can be used as a constant which only refers to material, specimen shape and stress-concentration factor Kt.Finally, the full-life fatigue crack growth rate equations are established under constant amplitude loading or spectrum loading conditions. Fatigue lives were calculated using these equations. Results from the tests and analyses agreed well. Thus, an efficient analysis methodology for predicting fatigue full lives is presented in this paper. |
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