Journal of Mechanical Science and Technology 33 (5) (2019) 1~6 www.springerlink.com/content/1738-494x(Print)/1976-3824(Online) DOI 10.1007/s12206-019-0406-y Effect of clearances in rolling element bearings on their dynamic performance, quality and operating life † Mostafa Yakout 1,* , M. G. A. Nassef 2 and Soheir Backar 2 1 Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada 2 Production Engineering Department, Alexandria University, Alexandria, 21544, Egypt (Manuscript Received August 19, 2018; Revised November 6, 2018; Accepted January 15, 2019) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract The performance of rolling element bearings is one of the machine quality measures in industry. The fatigue life and performance of rolling element bearings depends mainly on the dynamic characteristics of those bearings. This paper studied the effect of the internal radial clearance on the damping characteristics, natural modes of vibration, and fatigue life of rolling element bearings. Vibration modal analysis was performed on rolling bearings of the same size and type to measure their dynamic characteristics. These dynamic character- istics include the natural frequency of the first mode of vibration, damping, and amplitude of frequency response function at resonance. The internal radial clearances of these bearings were measured. A statistical analysis was performed to study the correlation between the internal radial clearance and the dynamic characteristics of rolling bearings. It was found that the damping ratio of the bearing assembly increased by reducing the internal radial clearance of the bearing. Similarly, rolling bearings that have large internal clearances showed short predicted fatigue life. It is concluded that the dynamic characteristics, and consequently the dynamic performance, of rolling bear- ings are significantly affected by the internal radial clearance. Keywords: Modal analysis; Internal radial clearance; Bearing life; Dynamic load rating; Dynamic characteristics ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction The performance of various machinery systems depends mainly on the dynamic characteristics of the rotating compo- nents (e.g., rolling element bearings), because most of those systems are subjected to dynamic cyclic loads while providing a relative rotational motion. The selection of rolling bearings is one of the challenges in many applications, especially cer- tain critical applications in the aerospace industry that require high performance [1-3]. According to the literature, rolling bearings of the same type and size do not exhibit the same performance under similar operating conditions. Manufactur- ing and assembly errors, which are the main source of error in rolling bearings, have a strong influence on the fatigue life of rolling bearings [4-9]. The internal radial clearance affects the load distribution, and consequently the fatigue life of rolling bearings. Zero radial clearance bearings generally have the highest fatigue life. The fatigue life of rolling bearings de- creases by increasing the internal radial clearance [10-13]. The performance and life of rolling element bearings are affected by damping and stiffness of bearing assembly [13]. Although the bearing manufacturers provide a formula to calculate the fatigue life of rolling bearings, predicting the actual fatigue life of those bearings is still one of the main challenges in bearing research [14-17]. The Lundberg-Palmgren life theory provides the same fatigue life index for bearings of the same size and type. However, the dynamic response of rolling bear- ings is affected by any variations in lubrication, clearances, and any other assembly error [16-24]. Experimental modal analysis has been recently used for determining the dynamic characteristics of complex structures and for predicting the fatigue life of single components and assembly structures [9, 25-34]. Previous research stated that these dynamic character- istics act as the deoxyribonucleic acid (DNA) characteristics of rolling element bearings, and represent a quality tool for predicting the performance and operating life of those bear- ings [9, 15, 27, 35]. Since the internal radial clearance has a strong influence on the fatigue life of rolling bearings [20], it is potentially expected that the internal clearance affects the dynamic characteristics of rolling bearings. It has been re- ported that the estimated bearing life can be enhanced by re- ducing the internal clearance. This estimated bearing life con- siders the rolling element size and static load (Stribeck factor) parameters only [20]. Also, the bearing life and dynamic load rating are affected by any variations in the dynamic character- * Corresponding author. Tel.: +1 905 979 4509 E-mail address: mohamemy@mcmaster.ca; yakout_mostafa@yahoo.com † Recommended by Associate Editor Gyuhae Park © KSME & Springer 2019