Coefficient of friction of binary granular mixtures in contact with a smooth wall. Part B. Micro-structural model describing the effects of packing fraction and load distribution on the wall friction of smooth, elastic spheres

A micro-structural model is developed capable of predicting the magnitude o f the wall, friction coefficient of an assembly of smooth particles in cont act with a smooth wall surface. The model is based on the Adhesion Theory o f Friction of Bowden and Tabor (1964, Friction and Lubrication of Solids, P art-II. London: Oxford up.) and represents an extension to binary mixtures of an earlier model proposed by Tuzun, Adams and Briscoe (1988, Chemical En gineering Science, 43, 1083) for assemblies of mono-sized particles. A fini te element computer code is used to investigate the load distribution betwe en different size particles in contact with a flat wall under the action of a compressive load acting on a static assembly. A micro-structural model i s proposed limited to the maximum packing fraction of the binary mixtures w here negligible re-arrangement of particulate assembly is allowed to occur during sliding next to a flat wall surface. The proposed micro-structural m odel predicts the variation of the wall friction coefficient with normal lo ad as a function of the particle contact density and the load distribution between the coarse and fine particles at the maximum possible packing fract ion. These predictions are compared with the results of the direct shear bo x experiments described in Part A of this series of papers (Abou-Chakra gr Tuzun, 1999, Chemical Engineering Science). Encouraging agreement is report ed between theory and experiment. (C) 1999 Elsevier Science Ltd. All rights reserved.