Fretting fatigue strength of specimens subjected to combined axial and transversal loading

The theoretical and experimental considerations presented in this paper refer to flat specimens, with a special bridge clamped to their surfaces, subjected to axial cyclic loading, transversal clamping load, and a friction force appearing on contacting surfaces. The theoretical analysis shows that the highest tensile stress exists at the edge of the bridge along with the maximum level of an elastic strain energy. The fatigue experiments and the metallographic examinations of the specimens proved the theoretical assumption that the fatigue crack propagates in such a direction, that the total strain energy decrease, caused by the crack growth, is maximum. The main crack, which is responsible for the final fracture of the specimen, originates from the edge of the bridge, propagates initially at a 45° angle to the surface and, while growing, gradually becomes perpendicular to the surface. The paper also presents a theoretical approach to the conditions of development of short fatigue cracks remaining in the area of residual stresses appearing as the result of clamping pressure. The linear theory of fracture mechanics has been applied to calculate the range of the stress intensity factor in the specimen and the fretting fatigue limit of the junction. The result of the experiments conducted with carbon steel are generally in good agreement with the calculations.