Doctor of Philosophy (PhD)
This dissertation is devoted to a theoretical and experimental study of the granular contact lubrication, both. The theory is based on the kinetic of the granular material where the granules interact with each other and with the boundary surfaces through instantaneous, binary collisions, characterized by a constant coefficient of restitution. Specifically this study focuses on granular lubrication in Couette flows. A series of simulations is reported and the results show good agreement with several published papers. Also, a theory that ties the true temperature to the grain mobility is developed. The true temperature of a granular material depends on the balance between the source of energy and the dissipation of energy due to inelastic collisions. In treating rapid shearing regime the collision is generally considered to be instantaneous. However, in a dense regime and at relatively small sliding speeds, the contact time between the granules is larger than the time between collisions and thus the friction between the granules starts to play an important role. Therefore, the effect of enduring contact becomes dominant over that of the kinetic and collisional stresses. The enduring contact between granules is into consideration by making use of Coulomb friction model. The results reveal that the enduring contact is a strong function of the solid volume fraction and its effect tends to dominate the solution at relatively small sliding speeds. A series of experimental investigations is presented that demonstrate the lift phenomenon observed in an annular shear cell apparatus. The effects of the friction coefficient and the surface roughness are expressed as a function of the rotational speed and the applied load. The theoretical results and the experimental measurements are compared. The results of experiments provide a unique quantitative evidence for the measure of the phenomenon of the lift. Furthermore, a series of experimental investigation on the nature of stick-slip associated with granular materials sheared at low speeds is demonstrated. The results reveal the occurrence of stick-slip at low speed. The behavior of the stick-slip is similar to the results presented by several researchers interested in physics and geology fields.
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El Kholy, Karim, "Granular Contact Lubrication: Theory and Experiment" (2007). LSU Doctoral Dissertations. 1718.