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.

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.

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.