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

Abstract

A micro-structural model is developed capable of predicting the magnitude of the wall friction coefficient of an assembly of smooth particles in contact with a smooth wall surface. The model is based on the Adhesion Theory of Friction of Bowden and Tabor (1964), Friction and Lubrication of Solids, Part-II. London: Oxford up.) and represents an extension to binary mixtures of an earlier model proposed by Tüzün, Adams and Briscoe ( 1988, Chemical Engineering Science, 43, 1083 ) for assemblies of mono-sized particles. A finite element computer code is used to investigate the load distribution between 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 is proposed limited to the maximum packing fraction of the binary mixtures where negligible re-arrangement of particulate assembly is allowed to occur during sliding next to a flat wall surface. The proposed micro-structural model predicts the variation of the wall friction coefficient with normal load as a function of the particle contact density and the load distribution between the coarse and fine particles at the maximum possible packing fraction. These predictions are compared with the results of the direct shear box experiments described in Part A of this series of papers (Abou-Chakra & Tüzün, 1999, Chemical Engineering Science). Encouraging agreement is reported between theory and experiment.