Browsing by Subject "Tribology"

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    Investigation of Asphalt Mixtures Compaction Using a Novel Approach Based on Tribology
    (Center for Transportation Studies, University of Minnesota, 2020-12) Yan, Tianhao; Turos, Mugurel; Kumar, Ravi; Marasteanu, Mihai
    Compaction is one of the most important factors that affects the durability of asphalt pavements. Many studies have been focused on developing methods to improve compaction. Previously, the authors found that the addition of small percentages of Graphite Nanoplatelets (GNPs) significantly increase the compactability of asphalt mixture. Traditional viscosity test results show that the increase in compactability is not a result of viscosity reduction, which implies that other mechanisms are responsible for the increase in compactability of GNP modified mixtures. This study investigates the lubricating behavior of the binder. A new test method, referred to as a tribological test, is conducted to evaluate the lubricating behavior of binders modified with different percentages of GNP (0%, 3%, and 6%). To better simulate the roughness of the aggregate surface, the tribological fixture is modified using textured contact surfaces instead of smooth ones. The results of rough surface tribological tests show that the addition of GNPs increases the lubrication behavior of the thin film binder between rough surfaces. It is hypothesized that the increase in compactability can be attributed to the increase in the lubricating behavior of the binder due to the addition of GNP.
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    Lubricity of biomedical conduits
    (2013-12) Turner, Thomas James
    The research is motivated by the need to explore the inputs and mechanisms responsible for the creation of beneficial tribological coatings on medical grade silicone rubber tubing and how to quantify them. Despite the fact that biomedical conduits are routinely made lubricious by a host of different methods, there is an insufficiency in the present state of knowledge with regard to how to precisely quantify conduit bore lubricity. Test methods, newly invented, to characterize tubing bore lubricity are described in detail with greater emphasis on the extraction of coefficients of friction relative to historical testing methods. A new invention for characterizing the lubricity of biomedical conduits makes use of a pressure cuff or air-bladder to compress a plasma-treated silicone tubing sample onto a friction element. The instrument setup is a metal sliding-friction-element/silicone- tubing system. The tubing is stationary while the friction element that has been inserted into the tubing bore is pulled. The tubing is held in place with a known and regulated pressure, which allows the normal force pressing on the sliding component to be known. The pull force (tangential force) is registered and recorded using a commercial pull-test frame. Knowing the normal and tangential forces means that the coefficient of friction for the system can be extracted using this instrument.The running-in behavior observed during biomedical conduit friction assessment is quantified and a hypothesis regarding its source is set forth. The theme of the hypothesis is that material related to the constituents of silicone rubber is taken up by the friction element (coil, in this case) over several test cycles and thereby alters the system until it stabilizes. Subsequently, the coil becomes equilibrated with the chemical makeup of its environment, and this is why the resistance force stabilizes. The results of extensive experimentation showed that pristine coils displayed markedly more running-in phenomenon when compared to either an exercised coil or a stored-in-silicone tubing coil.The outcome of the thesis is a thorough understanding of tubing bore lubricity quantification.