| Fretting fatigue leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Since fatigue life reduction caused by fretting fatigue occurs in various mechanical components, such as bolted connections and blade/disk dovetail joints etc., fretting fatigue is regarded as an important issue in the design of aerospace structures. Consequently, a number of studies have been performed to predict the behavior of fretting fatigue. However, while many studies have evaluated fretting fatigue behavior under elastic deformation conditions, few studies have focused on fretting fatigue behavior under elastic-plastic deformation conditions. Due to the fact that plastic deformation is an integral part of crack nucleation, the role of plastic deformation in crack initiation should be considered, especially when a large plastic zone is presented. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity.; Experimental tests were performed using pad configurations involving elastic-plastic deformations. A total of eight different configurations of fretting pads were used for this dissertation. Five of the eight geometries were intended to generate the elastic deformation, i.e. 50.8 mm, 101.6 mm and 304.8 mm radius pads with normal contact load of 1.334 N, 2.224, and 4.003 kN respectively and two flat with rounded edge pads with normal contact load of 1.334 and 4.003 kN. In order to replicate the elastic-plastic deformation conditions, the smaller radii of the cylindrical pads, i.e. 5.08 mm radius pads, and flat pad type3 (FP3) with smaller edge radius, were included in this study. Two different contact loads were applied with the 5.08 mm radius cylindrical pad, i.e. 1.334 and 1.779 kN, while one contact load was applied with the flat pad type3, i.e. 4.003 kN. The crack initiation location was found near the trailing edge under both elastic and elastic-plastic fretting fatigue conditions. The crack initiation orientation was also measured and found to have similar angles for all pad configurations involving both elastic and elastic-plastic deformation.; In order to calculate stress distributions under elastic-plastic fretting fatigue conditions, finite element analysis (FEA) was also performed. In order to obtain accurate stress and strain results, the mesh size was determined through comparison with FEA and analytical solution, i.e. Ruiz Program. The applied loading conditions obtained during experimental works were utilized in the FEA. (Abstract shortened by UMI.)... |
