J Fail. Anal. and Preven. (2011)11: 158-166 DOI10.1007/11668-0109422-z TECHNICAL ARTICLE-PEER-REVIEWED Fatigue Failure Analysis of a Grease-Lubricated Roller bearing from an electric motor Zhi-Qiang Yu. Zhen-Guo Yang Submitted: 16 August 2010/in revised form: 30 November 2010/ Published online: 22 December 2010 C ASM International 2010 Abstract The grease-lubricated roller bearing of an elec- a roller bearing [1-4], failures of lubricating grease may be tric motor that drove a supply blower suddenly failed during the predominant cause of failure. The failed greases gen- operation. In order to identify the causes of the failure, a erally suffered from physical, chemical, and thermal variety of characterizations were carried out. The failed degradations during bearing operation [5-8], and the deg- surfaces of the bearing were observed visually and micro- radation brought about the loss of lubricating capacities, copically, and the characteristics of the lubricating grease especially under high temperatures and high velocity con were also investigated. Results showed that the surface of the ditions. Physical changes are commonly involved with the inner ring of the bearing contained contact fatigue damage, increase of oil separation, the loss of thickener structure, ind was covered with a multitude of debris and contact and the reduction of base oil content [9]. Chemical changes fatigue pits. What's more, the lubricating grease was sub- are mainly due to oxidation of base oil and thickener and jected to severe thermally induced degradation due to high loss of antioxidant additives, which will consequently service temperature, which consequently resulted in the increase the amount of acidic species and high-viscosity decrease of the lubricating capacity of the grease. Thus, the products. Komatsuzaki et al. [10] showed that the loss of lubricant film in the roller/raceway contacts was not formed base oil was generally caused by the evaporation of volatile effectively and the lubrication of the roller bearing was poor. oxidation products and was the predominant factor con- As a result, serious local wear as well as contact fatigue trolling the lubrication life of grease in cylindrical roller damage were brought about on the roller and raceway and the bearings wear finally led to the failure of the bearing most common failure event that results fror lubricating greases in rolling-element bearings is surface Keywords Bearing failure. Contact fatigue damage contact fatigue [11]. According to this failure mode, cracks Greases lubrication Lubricant degradation usually initiate at or near the contact surfaces, and subse quently form microscopic pits, which will then act as the stress concentration sites for further damages 3, 11] during Introduction continuing bearing operation. What's more, such stress concentration sites on the contact surfaces interact with Roller bearings are significant components of supply other pre-existing defects ing handling damage blower motors and play a critical role in normal operation surface inclusions, and dents to formed solid particles of the blower, although many factors can lead to failures of entrapped in the lubrication fluid [3]. These particles will accelerate the initiation of cracks and promote additional This article will present a failure analysis of one grease lubricated bearing that was sealed at the driving end of a Z.-Q.Yu()·Z.G.Yang Department of Materials Science, Fudan University, supply blower motor that had a rotation speed of 990 r/min Shanghai China in the electric power unit. The bearing was a cylindrical e-mail:yuzhiqiang@fudan.edu.cn roller bearing with 18 rolling elements. The face materialTECHNICAL ARTICLE—PEER-REVIEWED Fatigue Failure Analysis of a Grease-Lubricated Roller Bearing from an Electric Motor Zhi-Qiang Yu · Zhen-Guo Yang Submitted: 16 August 2010 / in revised form: 30 November 2010 / Published online: 22 December 2010 © ASM International 2010 Abstract The grease-lubricated roller bearing of an elec￾tric motor that drove a supply blower suddenly failed during operation. In order to identify the causes of the failure, a variety of characterizations were carried out. The failed surfaces of the bearing were observed visually and micro￾scopically, and the characteristics of the lubricating grease were also investigated. Results showed that the surface of the inner ring of the bearing contained contact fatigue damage, and was covered with a multitude of debris and contact fatigue pits. What’s more, the lubricating grease was sub￾jected to severe thermally induced degradation due to high service temperature, which consequently resulted in the decrease of the lubricating capacity of the grease. Thus, the lubricant film in the roller/raceway contacts was not formed effectively and the lubrication of the roller bearing was poor. As a result, serious local wear as well as contact fatigue damage were brought about on the roller and raceway and the wear finally led to the failure of the bearing. Keywords Bearing failure · Contact fatigue damage · Greases lubrication · Lubricant degradation Introduction Roller bearings are significant components of supply blower motors and play a critical role in normal operation of the blower, although many factors can lead to failures of a roller bearing [1–4], failures of lubricating grease may be the predominant cause of failure. The failed greases gen￾erally suffered from physical, chemical, and thermal degradations during bearing operation [5–8], and the deg￾radation brought about the loss of lubricating capacities, especially under high temperatures and high velocity con￾ditions. Physical changes are commonly involved with the increase of oil separation, the loss of thickener structure, and the reduction of base oil content [9]. Chemical changes are mainly due to oxidation of base oil and thickener and loss of antioxidant additives, which will consequently increase the amount of acidic species and high-viscosity products. Komatsuzaki et al. [10] showed that the loss of base oil was generally caused by the evaporation of volatile oxidation products and was the predominant factor con￾trolling the lubrication life of grease in cylindrical roller bearings. The most common failure event that results from failed lubricating greases in rolling-element bearings is surface contact fatigue [11]. According to this failure mode, cracks usually initiate at or near the contact surfaces, and subse￾quently form microscopic pits, which will then act as the stress concentration sites for further damages [3, 11] during continuing bearing operation. What’s more, such stress concentration sites on the contact surfaces interact with other pre-existing defects including handling damage, surface inclusions, and dents to formed solid particles entrapped in the lubrication fluid [3]. These particles will accelerate the initiation of cracks and promote additional debris production [12]. This article will present a failure analysis of one grease￾lubricated bearing that was sealed at the driving end of a supply blower motor that had a rotation speed of 990 r/min in the electric power unit. The bearing was a cylindrical roller bearing with 18 rolling elements. The face material Z.-Q. Yu (&) · Z.-G. Yang Department of Materials Science, Fudan University, Shanghai, China e-mail: yuzhiqiang@fudan.edu.cn 123 J Fail. Anal. and Preven. (2011) 11:158–166 DOI 10.1007/s11668-010-9422-z