Because of the complex nature of the fatigue process, it is only recently that reasonably effective analysis procedures for predicting finite-fatigue life for simple notched coupons have evolved. One of the more vexing problems in adapting these procedures to making life predictions for complex components and structures is that of the multiplicity of crack initiation sites and mechanisms which determine the fatigue life of such structures. It has been observed that which of the many potential initiation sites and mechanisms controls failure depends on the service environment and the magnitude and character of the service loading. The present paper critically examines available technology for fatigue analysis of complex structures in which the multiplicity of initiation sites and mechanisms control the structure’s life. It was concluded after this critique that those techniques most likely to yield accurate predictions were based on the critical location concept. Thereafter, the complexities in the use of this concept in fatigue analysis of components and structures were detailed and the concept illustrated by its application to the fatigue analysis of a component configuration which simulates a joint in an airframe. Finally, the use of the critical location concept as an aid to understanding the mechanisms of fatigue improvement fasteners was discussed.

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