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Fretting fatigue is an important fatigue failure mechanism iu aircraft structures, such as mechanically fastened lap joint components. It i s well known that multiple site fatigue crracking was originated from fretting damages especially in aging aircrafts and these premature crackings due to the fretting threaten aircraft safety which was certified by the damage tolerant fail safe concept. Fretting damages are related with partial microslip at contact surfaces which are nominally-clamped and subjected to oscillatory loads. Xn this investigatioa a series of experimental tests were carried out to observe the crack initiation and propagation behaviors and the effects of related fretting parameters on fatigue life in Al%OU-T351 pfate. And elasto-plastic contact stress analyses were also performed to assess the stress and strain fields in the subsurface during fretting contact. Contact pressure and tangential farce were reveaIed as important parameters in determining crack initiation and propagation life. The strain-life and Smith-Watson-Topper(SWT) models sere evaluated to predict crack initiation life and to compare with test results. It turned out that the maximum strain amplitude at the contact interface was a predominant parameter for fretting crack initiation and the short crack propagation life became more important, when the contact pressure became higher.

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The simulated load spectrum is constituted for the automobile muffler structure using probabilistic random process with the measured load data. By applying obtained spectrum load and evaluating residual strength degradation and failure probability, its fatigue life is assessed on the basis of two parameter Weibull distribution. To determine the required strength degradation model parameters, experimental tests of fatigue life are also performed on the welded specimens with same condition as real muffler structure, and the result of specimen tests are processed using the maximum likelihood method.

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