The friction characteristic of a journal bearing with dimpled bushings manufactured using the machining and the chemical etching techniques is investigated. A series of experimental results is presented to examine the effect of dimples on the Stribeck curve. Load, oil type, dimple size, depth and shape are varied to explore their influence on the friction characteristics. It is shown that with proper dimensions of dimples, the friction performance of journal bearings can be improved, particularly for light oils. The results reveal that in mixed lubrication regime, the so-called secondary lubrication effect in the dimpled area is the main mechanism responsible for improvement of performance. Experimental results also indicate that a bushing with etched dimples over the entire circumference offer a better frictional performance than a bushing with dimples etched on half of its circumference.

The Stribeck curve plays an important role in identifying boundary, mixed, elastohydrodynamic, and hydrodynamic lubrication regimes. Recent advances in elastohydrodynamic lubrication together with rough surface interaction have made it possible to develop a methodology for predicting the trend of the Stribeck curve. In this paper, we report the results of a series of experiments performed on a journal bearing together with a theoretical prediction of the Stribeck-type behavior. Various loads and oil temperatures are considered. The comparison between the experimental results with a mixed elastohydrodynamic lubrication model for line contacts is indicative of good agreement.

A series of experimental results is presented to explore the frictional characteristics of a grease-lubricated journal bearing. Load, grease type, and bushing material are varied to examine their effects on the friction coefficient. The results attest to the existence of distinctive regimes in grease lubrication akin to the oil-lubricated Stribeck curve. A mixed elastohydrodynamic lubrication model for line contacts is employed to estimate the coefficient of friction in mixed lubrication regime. The simulation results capture the basic characteristics of mixed lubrication.

A distinctive behavior of an oil-lubricated journal bearing undergoing oscillatory motion is the evolution of friction hysteresis as it traverses from boundary, to mixed, and to hydrodynamic regime. In this paper, the results of a series of experiments are reported to examine the effects of load, with or without oil, oil type, oil inlet temperature, and oscillating frequency on the friction hysteresis. Three types of hysteresis loop were found. The inertia of the lubricant flow contributes to the friction hysteresis.

A series of experiments was performed to study the behavior of grease-lubricated journal bearings. The results reveal that an oscillatory bearing undergoes a transition from boundary, to mixed, and to hydrodynamic regime. Another distinct feature is friction hysteresis that occurs as a result of oscillation. In this paper, we examine the effect of load, oscillating frequency, and lubricant on the friction hysteresis loop.