The Evolution of Surface Damage in Press-Fitted Shaft According to the Bending Stress

Abstract

Fretting damage is a critical problem to prevent failure of press-fitted shaft such as the rotor of a steam turbine, railway axles or coupling. To clarify the characteristics of surface damage due to fretting in press-fitted shaft, experimental methods were applied to small-scale specimen with different bending load conditions. Fatigue tests and interrupted fatigue tests of press-fitted specimen were carried out by using a rotate bending fatigue test machine. Macroscopic and microscopic characteristics were examined using scanning electron microscope (SEM), optical microscope or profilometer. It is found that small fatigue cracks are nucleated early in life regardless of bending stress, and thus the most portion of fatigue life on press fits can be considered to be crack propagation process. Most of surface cracks are initiated near the contact edge, and multiple cracks are nucleated and interconnected. Furthermore, the fretting wear rates at the contact edge increase rapidly at the initial stage of total fatigue life. It is thus suggested that the fatigue crack nucleation and propagation process is strongly related to the evolution of surface profile by fretting wear in press fits.