The stress field near a contact edge in fretting fatigue tests depends on the deformation type at the contact edge. During one cycle of loading in a fretting fatigue test, nine types of the stress field, among which six are independent, can possibly exist. In this study, the detailed forms of the singular stress variation range near the contact edge, i.e., the differences of singular stress fields corresponding to the maximum and the minimum loads, have been theoretically analyzed. The theoretical results were compared with numerical results obtained by the boundary element analysis. It was found that the singular order of the stress field obtained by the theoretical solutiong agrees well with the numerical results. It should be noted that the stress variation range presents different singular behavior for different deformation types. Therefore, the fatigue strength evaluation should be carried out in a manner corresponding to the stress variation range type. It was found that a fretting fatigue crack was initiated in the maximum shear stress range direction, and then kinked into the maximum tangential stress range direction following the initiation stage of the crack.

der mixed mode condition, and its growth behavior can be well characterized by using the parameter △Ki=△, which corresponds to the energy release rate. It is also found that the crack propagation resistance decreases with increasing of the porosity of the top ceramic coating. The crack propagation resistance at elevated temperature becomes lower compared to that at room temperature.

A theoretical method for estimating the elastic-plastic stress singularity at the interface edge of bonded power-law materials is proposed, based on the iterative approach developed in this study, It is found than the elastic-plastic stress singularity depends on the bonding angle and the larger hardening exponent the stress singularity becomes. Moreover, the elastic plastic stress singularity disappears when the bonding angle is smaller than 45

The problem studied in this paper is that of a coated semi-infinite plane subjected to a concentrated force in the upper thin layer (or film). The elastic properties of the coating material are different from those of the substrate, and a perfect bond is assumed between the two materials. The exact solutions of stress functions in a series form are obtained by the method of image. The terms in series form of the stress functions correspond to the image points from the lower order to the higher. The recurrence relations of the stress functions are given, i.e., the stress functions corresponding to the higher order image points are determined by the lower ones. Hence, from the original stress functions for an infinite plane subjected to a concentrated force, the explicit formulas of all terms of the stress function series can be derived. Also, through comparisons between the theoretical results and the numerical results by FEM, it is verified that the convergence rate of the solutions is very rapid, In most practical cases only the first several image points are sufficient to ensure the accuracy of the solution.

A large number of research works have been devoted to fretting fatigue from both mechanical and metallurgical viewpoints. In the present paper, fracture mechanical approaches for evaluating fretting fatigue life and strength have been briefly reviewed. Furthermore, a new approach based on a singular stress field near the contact edge and on fracture mechanics has been proposed. The directions of crack initiation and propagation as well as fretting fatigue life, which have coincided with the experimental results, could be estimated according to the new approach, in which singular stress near the contact edge and mixed mode crack growth have been taken into consideration. In the application of the new method to predict the fretting fatigue behavior, there are still several problems to be clarified, which have also been discussed in detail.