Modelling of acoustic emission generated in spur gear pair and rolling element bearing

Abstract

Gears and bearings are the most important components which are widely used in various applications such as automobiles, industrial machines, power plants, etc. The failure of these components is one of the most frequent causes of the machine breakdown. Hence, health monitoring or fault diagnosis of gearboxes and bearings is an important aspect to prevent unwanted shutdowns/catastrophic failures of the machines in advance and to ensure reliability and low operating cost. Various techniques like vibration monitoring, acoustic measurements, thermography, ultrasonic testing, acoustic emission (AE), and wear debris analysis etc. are used for condition monitoring of gearboxes and bearings. AE is a very effective technique for the health monitoring and diagnostics of rotating machine components. Several experimental investigations have been found in the literature which show the effectiveness of AE in identifying the fault/defect in gears and bearings. The literature reviewed has revealed that gear operating parameters as well as bearing operating parameters such as speed, load, specific film thickness of lubrication, and temperature strongly influence the AE energy during the operation of gears and bearings. It has also been identified that the presence of the defect on the gear tooth and bearing elements as well as defect size strongly affects to the AE level. Furthermore, it has been concluded in the experimental studies that asperity contact is a potential source of AE generation during the operation of gears and bearings. A fine correlation between asperities contact and AE value has been reported. But, there is no theoretical or mathematical model available to comprehend the physical mechanism of AE generated during the gear and bearing operation. In this thesis, the theoretical or mathematical models are developed for spur gear pair and rolling element bearing for healthy as well as defected condition by using approaches of contact mechanics and linear elastic fracture mechanics. These mathematical models correlate the energy of AE to operational parameters of gears and bearings as well as parameters related to defect. The mathematical models are developed for AE generated in healthy spur gear pair, spur gear pair with crack, spur gear pair with pitting. The mathematical models are also developed for AE generated in rolling element bearing in healthy as well as defected condition i.e. defect on inner-race, outer-race, and rolling element. The developed models were validated on the basis of experimental studies and satisfactory results have been observed. It shows the potential of the developed models to perceive the AE generated during the gear and bearing operation which is the significant factor in the condition monitoring of spur gear and rolling element bearing. Keywords: Acoustic emission; gear; bearing; modelling; asperity contact; gear operating parameters; bearing operating parameters; friction; load sharing factor; lubrication; dynamic factor; crack; crack propagation; fracture; stress intensity; defect; surface topography; pitting; protrusion contact.