Investigation on Acoustic Emission Characteristics of Lubricating Grease in Hydrodynamic Lubrication Regime

Traditional methods for monitoring lubrication and wear typically rely on indirect indicators such as temperature changes, vibration, or lubricant contamination. However, these approaches have limitations in that they are unable to provide real-time, direct insights into the micro-scale interactions occurring between frictional interfaces. This paper aims to explore the mechanisms and characteristics of acoustic emission (AE) signals generated by lubricants, particularly greases, in hydrodynamic lubrication (HL) regime, thereby enabling early detection of surface wear and degradation in mechanical systems. Based on the fundamental theory of elastic deformation strain energy release from micro-asperities, a model for AE signals of lubricants in HL regime was established. Experimental studies using a rheometer platform were conducted on lubricants to compare their flow properties and related friction signals. The results indicate that both lubricating greases and oils share similar characteristics, where shear rate and lubricant viscosity are significant factors affecting AE signals. These findings provide essential references for monitoring the lubrication state of friction pairs and the health condition of lubricants, especially in detecting early surface wear.