Dynamics of a rigid shaft supported by angular contact ball bearings and experimental analysis of ball bearing faults

DYNAMICS OF A RIGID SHAFT SUPPORTED BY ANGULAR CONTACTBALL BEARINGS AND EXPERIMENTAL ANALYSIS OF BALL BEARINGFAULTS(Ph.D. Thesis)Tuncay KARAÇAYGAZİ UNIVERSITYINSTITUTE OF SCIENCE AND TECHNOLOGYJuly 2006ABSTRACTThe dynamic analysis of ball bearings are based upon the alteration ofthe forces due to the elastic deformation of a rolling element betweenthe inner and the outer rings in one full revolution with the cage. Hencethe resulting force will vary in amplitude and direction consideringthere is more than one rolling elements within a ball bearing. Weight ofthe shaft and external forces are compensated with the elasticdeformation between the inner, outer and rolling elements matchingsurfaces. Nonlinear characteristics of contact mechanics will furthercomplicate the behavior. In this study a rigid shaft supported by a pairof angular contact ball bearing is modeled in five degrees of freedomand nonlinear equations of motion are obtained. First, vibrationcharacteristics of shaft supported by healthy ball bearings areinvestigated, and then model is developed to investigate effects ofouter, inner and rolling element localized defects and distributeddefects such as off-sized ball and unbalance. In order to analyzedynamic response of the shaft-bearing system, equations of motion aresolved for different shaft rotation speed and results are presented intime, frequency and time/frequency domains all. Simulation resultsindicate that ball bearing faults can be effectively pointed out usingvibration analysis. Thus in the second part of this study a test rig wasset up and made run until it partly fails. Vibration signals acquiredduring experiment are analyzed with time, frequency andtime/frequency signal processing techniques and failure mechanismsof ball bearings are investigated. The wavelet analysis is found to beone of the effective techniques for fault diagnosis of ball bearing andthe application of wavelet with time and frequency domain techniquesis further increased the performance of the technique.Science Code : 914.1.003Key Words : Bearings, vibrations, shaft dynamics, predictivemaintanancePage Number : 192Adviser : Prof. Dr. Nizami AKTÜRK