Cyclic variations in friction forces and contact stresses during fretting fatigue

This paper analyses the cyclic variation in friction forces and contact stresses during fretting fatigue tests. The analysis is applied to uniaxial test specimens under cyclic loading and the action of a spherical fretting pad subjected to constant normal loading. Specifically, friction forces and stresses involved in partial slip and small amplitude global sliding between the surfaces in contact are examined. To calculate this variation of forces and stresses, the Mindlin and Deresiewicz [R.D. Mindlin, H. Dersiewicz, Elastic spheres in contact under varying oblique forces, J. Appl. Mech., 75 (1953) 327-344.] analysis of the friction forces under varying oblique forces and the explicit equations for the elastic stresses beneath a spherical contact proposed by Hamilton [G.M. Hamilton, Explicit equations for the stresses beneath a sliding spherical contact, Proc. I. Mech. E., 197C (1983) 53-59.] have been used. The variation of the stresses shows two characteristics not analysed previously. One is the out of phase variation of some components of the stress tensor at the contact surface and close below it, even when the fluctuating external loads are in phase. In situations of small amplitude global sliding between the contact surfaces, it is also shown that the amplitude of the equivalent Mises stress close to the contact surface decreases with increasing sliding amplitude. These phenomena may influence the fatigue behaviour of the element concerned and should therefore be considered in examining criteria for damage under fretting fatigue. (C) 1998 Elsevier Science S.A. All rights reserved.