Fretting Fatigue Behavior of Shot-Peened IN 100

The fretting fatigue behavior of shot-peened of IN 100 was investigated in this study. S-N curves were obtained for two different shot-peened intensities (7A and 12A) and were compared to those of unpeened specimens. Stress relaxation behavior under fretting fatigue was also investigated after their measurements were obtained using the Xray diffraction method. The crack initiation location and the crack angle orientation along the surface were determined using optical and scanning electron microscopy (SEM). Cracks initiated near the trailing edge and on the contact surface for both 7A and 12A shot-peened specimens. Finite element analysis was performed using commercially available software, ABAQUS, to obtain contact region state variables such as stress, strain and displacement. These state variables were needed for the computation of fretting fatigue parameters, such as stress range, effective stress, shear stress range (SSR) and modified shear stress range (MSSR), which were further analyzed. It was found that there was relaxation of residual compressive stress during fretting fatigue up to a certain depth. The effects of shot-peening were negated relatively early in the fretting fatigue life. There was little difference in fretting fatigue life between the two intensities of shotpeening, but there was an improvement in relation to unpeened specimens. Also, the MSSR parameter, a critical plane based fatigue parameter, was effective in characterizing the fretting fatigue behavior in terms of fatigue life, crack initiation location and orientation. However, it is not applicable to both shot-peened and unpeened cases simultaneously to yield a single trend. This may be due to the peened specimens having been plastically-deformed on the surface and the unpeened specimens remain unchanged, and hence they were two different types of material which did not to act the same way under fretting fatigue conditions.