The rolling contact (RC) fatigue test rig was developed specifically for rapid and inexpensive evaluation of materials and processes for rolling element bearing applications. The simple geometry of the test specimen, a cylindrical bar, makes it ideal for evaluating new materials where only limited quantities of the material may initially be available and also permits precise control of the mechanical and thermal processing of the test specimen.

Contact fatigue failure is a common problem experienced in many applications such as bearings, gears, and railway tracks. In recent years, research companies have developed finishing processes that aim to improve components' contact fatigue life. Preliminary rolling contact fatigue tests have shown that superfinishing processes could potentially improve a component's contact fatigue life by 300 %. However, before these technologies can move from the laboratories to industrial platforms, more tests are needed to verify the claim. The objective of the work herein is to discuss the completion and verification of a sliding-rolling contact fatigue (S-RCF) test rig. This project is funded by the U.S. Army to assess the real benefit of superfinishing on the contact fatigue life of gears used in helicopter transmission boxes. The proposed tester design uses three rollers around a specimen, a hydraulic loading mechanism, and two servo motors. This configuration of the S-RCF tester allows for shorter testing time, more flexible testing parameters such as any combination of slide-roll ratio between the surfaces, any operating speed, and dry or lubricated testing conditions. Failure is detected with a state-of-the-art eddy current crack detection system, which can also be used to monitor and investigate crack growth for different materials, levels of superfinish, and operating conditions. Preliminary tests on a common gear material (AISI 8620 steel) were performed to assess the mechanical limits as well as the control software performance. This paper presents the detailed development and validation of the tester. It discusses issues involved with servo controllers, electronic gear ratio, and their ability to provide precise speed and slip ratios.

In order to gain detailed insight into the processes taking place during rolling contact fatigue (RCF) and rolling contact wear, the test machine used must be closely controllable and offer comprehensive data collection facilities. This paper describes a machine that has been developed to offer these facilities over a wide range of test conditions, and that has the facility for the early detection of cracks by an eddy current method.

The proceedings of a November 1996 conference in New Orleans, update previous information and present new materials and processing relating to steel for the anti-friction bearing industry. Among other subjects, they cover steel cleanliness and measuring methods, bearing fatigue life, advanced steel

Few rolling bearing users realize that the fundamentals of bearing life predictions are based on experimental data derived under conditions very different from the ones generally used in RCF testing today. The basic life formulas derived in the 1940s largely were based on tests run on steel with very different characteristics than the materials used to produce bearing components today. Still, the fundamental life calculations are based on the (C/P)n concept, which was experimentally derived by Lundberg and Palmgren (Lundberg, G. and Palmgren, A., "Dynamic Capacity of Rolling Bearings," Acta Polytech. Scand., Mech. Eng. Ser., Volume 1, No. 3, 1947), even if the basic equation has been expanded and adjusted to reflect the lives recorded for modern bearings and to incorporate the concept of a fatigue limit (Ioannides, E., Bergling, G., and Gabelli, A., "An Analytical Formulation for the Life of Rolling Bearings," Acta Polytech. Scand., Mech. Eng. Ser., Volume 137, 1999, pp. 9-12, 21-24). In an attempt to better understand the premature and unpredictable failures that sometimes occur in certain industrial applications today, the test procedures used by Lundberg and Palmgren have been revisited, and data have been derived that might contribute to an understanding of the short lives sometimes experienced in certain industrial bearing applications. Based on this test procedure, a better understanding of the development of micro-crack associated plastic deformations at non-metallic inclusions also has been gained. The propensity of different non-metallic inclusions to drive the formation and growth of micro-cracks has been studied in detail, and this knowledge has been used to develop steel that is less prone to butterfly development and micro-crack growth under very high contact stress conditions. Today's bearing life prediction models presume that the Palmgren-Miner rule of accumulated damage is globally applicable. Experimental data questioning this assumption are presented.