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1915 |
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Design and Testing of a Tribometer for In Situ Microscopy |
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Other: Precision Assembly |
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A tribological contact can be a severe environment for even the most robust material. High localized pressures and temperatures at asperity peaks can lead to a wide variety of wear regimes and chemical events that ultimately lead to the failure of a bearing surface.
Wear rates can be measured in a variety of ways. Mass measurements can be taken before and after tests to provide an average wear rate provided that the materials of interest do not uptake or outgas in the test environment. A wide range of commercially available profilometers, interferometers, and optical and electron microscopes can be used to geometrically characterize material loss once a test is complete.
It can also be desirable to have real-time wear measurements to observe initial run-in periods or sudden catastrophic failures. One approach is to monitor the relative normal displacement between two surfaces, then calculate a wear rate from knowledge of the contact geometry. This can be troublesome if both components of the contact are simultaneously wearing. Chemical events can also be monitored in real time through the use of in-situ spectroscopy [1].
Given these requirements, we have developed a tribometer that is easily adapted for use under multiple microscopes. When chemical bond changes are of interest, a Raman/Fourier Transform Infrared (FTIR) spectroscopy unit can be used to observe the contact through a transparent ball on flat contact. If wear evolution is a concern, a scanning white light interferometer (SWLI) can be used to monitor the wear of specific regions after each pass rather than at the end of the test. Optical microscopy can be applied to visually inspect the counterface for wear or wear debris during testing. Additionally, Polyetheretherketone (PEEK) insulators can be added to allow electrical contact resistance testing.
The tribometer makes use of a lead screw and servo-motor driven stage to overcome frictional forces and generate relative motion. Rotary encoder feedback and data acquisition hardware and software are used to ensure translational repeatability. The normal load is set at the beginning of a test with a manual vertical stage. Normal and friction loads are resolved and monitored using a six degree-of-freedom load cell. A parallelogram-type leaf spring flexure design helps maintain alignment of the contact as the species wear.
1. Wahl, K.J., Dunn, D.N., and Singer, I.L., Wear, 230 (1999) 175-183. |
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