Includes a title page in Arabic

Thesis (Ph.D.) Doctoral Egypt - Japan University of Science and Technology (E - JUST) - School of Innovative Design Engineering - Industrial and Manufacturing Engineering Department 2024

.Rolling element bearings (REBS) are essential components in rotating machinery , providing support and minimizing friction between moving and stationary parts Despite their widespread use , REBs are susceptible to failure due to localized defects and skidding damage , which can significantly reduce their lifespan and performance Rolling contact fatigue, electric erosion, and plastic deformation lead to the formation of localized defects on REB surfaces , such as spalls, dents, or bumps These defects increase vibration levels and compromise machinery reliability , potentially leading to severe damage or catastrophic failures if undetected early Moreover , skidding damage is considered one of the leading causes of wear mechanisms in REBS , and it accelerates the presence of localized defects. Despite extensive research on the investigation of REB dynamic behavior , the combined effect of different defect types on bearing vibrations has been relatively understudied Also , only a few REBS dynamic models considered cage flexibility , and a little effort was focused on the effect of lubricant types on the REB Skidding behavior In this study, a 6-DOF dynamic model is developed to investigate the vibration characteristics of REB with a multipoint defect comprising a dent and bump on its raceway surface The model considers various factors such as time-varying contact forces due to defects , lubricant film damping , bearing preload , and the inertia effect of rolling elements Additionally , the impact of lubricant characteristics on REB skidding is explored at different speed states using an improved nonlinear skidding dynamic model The model incorporates time-varying traction coefficient , cage flexibility , and cage pocket clearance The tested lubricants are lithium grease (LGT2), compound calcium sulfonate (CCS) grease , and 4109 Chinese aviation oil The simulation results indicate that vibration patterns are significantly affected by defect type , size , and angle between defects In addition , it highlights the challenge of predicting bearing defect parameters solely from acceleration signal analysis , emphasizing the need for jerk signal analysis Furthermore , simulation results indicate that lubricant properties significantly affect REB dynamic performance , influencing cage slip ratio , roller - raceway sliding velocity , and cage-roller impact force Notably , CCS grease exhibits superior efficiency across all operating conditions , attributed to its structural strength , shear stability , and high oil release rate This study provides valuable insights for enhancing the stability , reliability , and safety of rotating machinery by facilitating early fault detection and diagnosis of REBs Additionally , it underscores the importance of selecting appropriate lubricants tailored to specific operating conditions

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