Date of Award

8-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Abstract

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 which aim to improve a component's contact fatigue life. One such process has been patented by REM Chemicals in Texas. Preliminary contact fatigue tests have shown that this superfinishing process could potentially improve a component’s contact fatigue life by 300%. Before this technology can move from the laboratory to an industrial platform, more tests are needed to verify the claim. To the best of the author’s knowledge, no standard process or test machine exists to assess the fatigue endurance of superfinished contacting surfaces.

The objective of this thesis is to discuss the completion and verification of a sliding-rolling contact fatigue (S-RCF) test rig. A majority of the development and fabrication was performed by a group of students at the University of North Dakota before May 2007. After this, completion of the tester was finished by the graduate student of this thesis. Unlike other contact fatigue testers built for specific purposes, the proposed tester allows for more flexible testing parameters such as any combination of slide-roll ratio between the surfaces, any operating speed and dry or lubricated testing. For failure detection, the proposed tester is equipped with a state-of-the-art eddy current crack detection system. However, it can be easily modified to use ultrasonic or vibration based crack detection devices. The eddy current crack detection system can also be used to monitor and investigate crack growth for different materials, levels of superfinish and operating conditions.

Three preliminary tests on a common gear material (A1S1 8620 steel) were performed mechanical limits as well as the software performance of the tester. Two of the 8620 specimens exhibited signs of failure during testing, while one specimen was suspended after running for several days. While the last specimen was being tested, a shaft broke and further testing could not be performed. The tester failure was caused due to poor manufacturing of the shafts and a slight misalignment of the rollers.

During the three tests, the various systems of the S-RCF tester were left running for several days and only minor problems were found. These problems were either inconsequential or fixed. Several Matlab scripts were developed and modified to control the tester and analyze the data online and offline.

The S-RCF tester has a few components that need to be fixed before further testing can be performed. Two options exist to continue testing. The first option is to repair the current S-RCF tester and continue testing. The second option is to design a second generation machine with several upgrades and improvements. Either option will provide the University of North Dakota's Engineered Surfaces Center the ability to test and compare the fatigue endurance for different surface finishes.

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