ASMEparticle - W. Gregory Sawyer Department of Mechanical...

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W. Gregory Sawyer Department of Mechanical Engineering, University of Florida, Gainesville, FL 32611 John A. Tichy Department of Mechanical Engineering, Aeronautical Engineering, and Mechanics, Rensselaer Polytechnic Institute, Troy, NY 12180 Lubrication With Granular Flow: Continuum Theory, Particle Simulations, Comparison With Experiment Studies of particle flows have followed three parallel paths: (1) experiment, (2) analysis based on the assumption of a continuum, and (3) direct particle simulation. In this paper, we perform continuum and particle analyses and compare them to each other, and to previously reported experiments. Both the particle simulations and the continuum model over-predict the experimental normal load and shear force, however, the trends and orders-of-magnitude are in agreement. The modeling approaches are based on first prin- ciples, and do not rely on curve fitting to obtain effective properties of the mixture such as viscosity or conductivity. @ DOI: 10.1115/1.1353178 # Introduction Over recent years there has been increasing interest in the pos- sible use of granular or powder mixtures as a means of applying solid lubrication. At temperatures greater than 500°C, conven- tional liquid lubricants cannot be applied and powder lubrication may be an attractive alternative. There are a number of other tribological applications in which particulate two-phase flow may play a role. The process of chemical-mechanical polishing ~ CMP ! , which is a subject of intense interest in electronics manufacturing to attain a high degree of planarity on silicon wafers, involves the thin film flow of a slurry of particles ~ Ali et al. @ 1 # and Tichy et al. @ 2 #! . The process of debris analysis for bearing diagnostics re- quires knowledge of such flows, Cho and Tichy @ 3 # . Particulate debris migration associated with lysis ~ an inflammatory bone re- action ! in artificial joint prostheses is a cause of failure, Poggie et al. @ 4 # . Our present study is concerned with the flow of non- deforming granules without a carrier fluid, and, thus, strictly speaking, would apply directly only to the powder lubrication case mentioned. However, this works study can form a basis for exten- sions to the true two-phase flow case. In this paper, we compare results of both continuum modeling and particle dynamic calculations to our existing experimental re- sults, Yu et al. @ 5 # and Yu and Tichy @ 6 # . Two modes operation are observed in the experimental shear cells. At low speeds, there are strong and long-lasting contact forces between the highly compacted beads and the surfaces. At some increased critical speed ~ in our apparatus at 100 s 2 1 ! , the upper surface lifts off as the beads mean free path increases due to increased agitation. We call this a transition to granular collision lubrication. The former regime could be called granular contact lubrication. If granular contact lubrication exists in a bearing, the global friction forces are due to persistent rubbing interactions within the ensemble of particles. The normal forces are carried by elastic or plastic com- pression of the particles in contact. If collision lubrication exists,
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ASMEparticle - W. Gregory Sawyer Department of Mechanical...

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