Fretting fatigue in a spherical contact

Abstract

This article describes different types of tests in fretting fatigue and different geometries for use in testing, comparing mainly cylindrical and spherical contacts and their corresponding advantages and disadvantages. Practical differences can be observed between these two types of tests regarding the alignment of the pads, the level of the loads to be applied, the rigidity in the test rig, the shape of the crack, the localization of the point of initiation of the crack, etc. The loads applied in spherical contact and stress distribution beneath the contact zone are described. As this stress state is multiaxial and non-proportional, the appropriate multiaxial criteria are needed in order to characterize the stress field. An equivalent stress is derived from the criteria and later related to the initiation of the crack. At the same time, with the use of the calculated stresses, a semi-analytical approach using a weight function is described for the determination of the stress intensity factor. The results of a series of fretting fatigue tests have been analysed. The initiation site, the orientation of the crack and, for the tests that did not fail, the length of the crack have been studied using a multiaxial fatigue criterion and linear elastic fracture mechanics (LEFM).