The transient tribo-dynamics and wear model are coupled to study the mixed lubrication-wear behavior during start-up. The coupled numerical model involves the film thickness equation with wear depth and a time-varying wear coefficient to account for the impact of transient mixed lubrication behavior on wear. In this study, the evolution of wear and mixed lubrication performance distribution over time is predicted, and the impact of acceleration mode, acceleration time, external load, lubricant viscosity, and start-up time on the numerical predictions is evaluated. The findings demonstrate that wear behavior, particularly in the analysis of the effects of acceleration mode and acceleration time, has a significant impact on the evaluation of the bearing-rotor system's start-up performance and even changes the determination of optimal parameters. Furthermore, the parametric study demonstrates that wear and mixed lubrication performance are sensitive to the external load and lubricant viscosity. Finally, studies on the effect of start-up times show that proper wear geometry promotes hydrodynamic effects, but severely worn bearing surfaces have a negative effect on start-up.
Rolling bearings operating in harsh environments are extremely exposed to the risk of exogenous dust or wear debris particles, so there is a strong need to investigate the effects of particulate contamination on bearing operation and to identify problems early. The lubricated oil containing silica particles of various sizes and concentrations are prepared and introduced into thrust ball bearings to replicate the severe operating conditions. Vibration and acoustic emission (AE) signals were measured by accelerometer and AE sensor in a thrust ball bearing test rig. The experimental bearing raceway was observed by scanning electron microscope (SEM) and confocal laser scanning microscopy, and the evolution of the surface topography was analyzed to probe the wear mechanism. The results show that the most severe wear areas occur at the bottom of the bearing raceway, and its degree of wear is significantly influenced by the size and concentration of the silica particles. As the experimental time increases, the raceway surface undergoes an accelerated wear process originating from slight dimples, which leads to bearing failure. Furthermore, the introduction of particles into the lubricant increases surface root mean square (RMS) roughness, vibration and acoustic emission for different experimental durations. The vibration and AE signals are affected by a combination of solid particles and surface wear. The measured monitoring results can provide valuable information about the damage morphologies and subsequently about the state of the bearing during operation.
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