Finite Element Analysis On Fretting Fatigue Contacting Stresses

Fretting damage is one of the most common damages in engineering. The initiation and growth of the crack at the contact areas can be accelerated quickly due to fretting damage, which reduces the fatigue strength and even causes security accidents.Finite element analysis software ANSYS was used to calculate the distribution of the stress on the contact surfaces of the cylindrical fretting pad model and flat fretting pad model. The influences of the vertical pressure, cyclic loading and the friction coefficient on the distribution of the stress on the contact surfaces and the effect of the contact stress on the initiation of fretting fatigue cracks were studied. The work and conclusions are as follows:1. The finite element model of the cylindrical fretting pad was established by ANSYS. The distribution of fretting contact stress was calculated. Compare with the Hertz contact theory calculated results, the errors are at 10% or less, which guaranteed ANSYS to fretting fatigue contact analysis feasible.2. As the vertical pressure increases, the surface tensile stress decreases, the maximum tensile stress increases, the compressive stress increases, and the shear stress at sticking zones decreases while increases at sliding zone. With the increase of cyclic loading, the tensile stress becomes larger, the compressive stress remains unchanged and the shear stress becomes larger at sticking zone, but basically unchanged at sliding zone. At sticking zone, the tensile stress decreases with the increase of friction coefficient, but increases at sliding zone. The friction coefficient has no influence on the compressive stress. The shear stress at sticking zone decreases with the increase of coefficient, however, at sliding zone it will increases.3. Three different fretting pad models were studied in the paper. It is found that under the same load conditions, the influences of micro-movements will decrease with the increase of the radius for cylindrical fretting pad model, and that a bigger stress mutation will occur at contact edge for flat fretting pad model.4. The distribution of shear stress formula was gotten through the curve fitting of the shear stress of sticking zone.5. MSR parameter and SSI parameter were used to predict crack initiation characteristics on a cylindrical fretting pad model with its radius 50mm. It is found that the crack initiation location is related to the shear stress increase and shear strain increase on contact areas, and that shear stress under the maximum cyclic loading will crack along 45°direction.6. The initiation of the fretting fatigue crack is mainly due to the effects of tensile stress on contact areas. The initiation of the crack is most likely to come up at the area of the maximum tensile stress, and the larger the maximum tensile stress is, the more easily the crack initiates.