Browsing by Author "Weick, Brian L."

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    Effects of fiber type on the tribological behavior of polyamide composites
    Weick, Brian L. (Virginia Tech, 1993)
    An experimental and analytical study of the tribological behavior of polymer composites is presented. Glass, aramid, and carbon fiber-filled polyamide (Nylon 6,6) composites serve as models for understanding friction and wear processes encountered when polymer composites are used in tribological applications. Experimental results not only include measurements of friction and wear, but surface temperatures produced by frictional processes during oscillating contact experiments. Since an optically flat, transparent sapphire disk is used as the oscillating countersurface, surface temperatures can be measured directly at the interface using an infrared microscope. Experimental results show that the presence of fibers in the polyamide matrix lowers wear, friction, and surface temperature when compared with the unfilled polymer. Rationale for this improved tribological behavior is presented and discussed. Fiber-type is shown to have a direct influence on the tribological behavior of the polymer composite, and the chemical behavior at and near the interface is shown to be significant by examining worn and transferred material through surface analytical techniques. In particular, evidence is presented for the tribochemical degradation of intramolecular bonds in the polyamide macromolecule. Measurements of surface temperatures are compared with theoretical predictions using models for the real area(s) of contact, and results from “scanning” experiments are also presented in which the infrared microscope is used to measure surface temperatures at possible real areas of contact within the apparent contact region. Instantaneous measurements of surface temperature and friction over a single cycle of motion are also presented which allows for the performance of a frequency domain analysis. This technique not only shows the frequency content of the friction and surface temperature signals, but it also shows correlations between these two parameters. The role of intermolecular attractions in frictional processes is addressed, and evidence for relatively strong intermolecular attractions between the polyamide surface and sapphire disk is discussed.
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    Infrared measurements of surface temperatures during oscillating/fretting contact with ceramics
    Weick, Brian L. (Virginia Tech, 1990)
    Surface temperatures generated by friction during osculating/fretting contact were measured using an infrared microscope coupled to a digital data acquisition system developed at Virginia Polytechnic Institute and State University. The contact geometry consisted of a stationary test specimen loaded against a vibrating sapphire disk driven by an electromagnetic shaker. Ceramic materials including zirconium oxide, sapphire, aluminum oxide, and tungsten carbide were used as test specimens since they are inert in air, and generate high surface temperatures when used in the oscillating contact system. Instantaneous fluctuations in surface temperature over a single cycle were measured and recorded. This information was compared with instantaneous friction force and velocity data. The friction force data was measured using semiconductor strain gages connected to a new octagonal ring designed specifically for this research. Zirconium oxide-on-sapphire experiments were performed at various loads, frequencies, and amplitudes. The resulting temperature rises, friction coefficients, heat generation rates, and wear scar sizes were compared. Surface temperature rises were measured as a function of position within the contact region. From this data, and scanning electron micrographs of the wear scars, inferences were made about the size, location, and distribution of real contact areas. Experimental measurements were compared with theoretical predictions obtained using a new numerical model developed by B. Vick and S. J. Foo.