A method for fatigue based reliability when the loading of a component is unknown

When the loading of a component is unknown, it is not possible to perform fatigue evaluation without some additional knowledge of the applied loading. A model is presented which considers problems of this type. In this situation, the components will have experienced some degree of fatigue damage during operation. However, the loading during use is unknown, and thus direct calculation of the remaining service life is not possible without additional data. The use of components removed from service to conduct fatigue tests can provide the required test data. The test data contains additional information associated with the loading which can be used to determine the residual fatigue damage resistance of the components. Comparing the residual fatigue damage resistance of the tested components with the fatigue damage resistance of new components can make it possible to, indirectly, describe the fatigue damage accumulation which has occurred in the components during the time in service. Thus, the fatigue damage accumulated in the components can be determined by additional fatigue tests, in spite of the absence of direct knowledge of applied service loading. The fatigue evaluation of untested components can be performed using the probabilistic fatigue model which is presented in this paper. The model is demonstrated by performing an evaluation of compressor blades for which the applied loading is unknown. The calculated results are shown to be close to the statistical results obtained in-service for the blades. (C) 1999 Elsevier Science Ltd. All rights reserved.