In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings were investigated. The fatigue life of the untreated and UNSM-treated needle roller bearings was evaluated using a roller fatigue tester at various contact stress levels, under oil lubrication conditions. It was found that the fatigue life of the UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with the untreated one. The results of the surface roughness and surface hardness of the needle roller bearings before and after UNSM technology were compared and discussed in order to understand the role of UNSM technology in improving fatigue life. It was found that the application of UNSM technology to the needle roller bearings can improve their fatigue life by reducing the friction coefficient and increasing the wear resistance, which may be attributed to the reduction in surface roughness from 0.50 µm to 0.15 µm and also the increase in surface hardness from 58 HRC to 62 HRC.
Slim bearings are used widely in aircrafts, robots, wind turbines, and industrial machineries, where their size and weight are very important for the performance of a system. The common materials of slim bearings for robots and industrial machineries are based on SAE52110 bearing steel, and special heat treatment and a super polishing process are used and adapted to improve the rolling contact fatigue (RCF) strength of bearings. The improvement in RCF strength, depending on contact stress, surface hardness, and the friction behavior before and after ultrasonic nanocrystalline surface modification (UNSM) treatment was validated. Simple analysis shows that these improvements can reduce the size and weight of slim bearings down to about 3.40–21.25% and 14.3–26.05%, respectively. Hence, this UNSM technology is an opportunity to implement cost-saving and energy consuming super-polishing, a heat treatment process, and to reduce the size and weight of slim bearings.
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