A single-particle friction cell for measuring contact frictional properties of granular materials

Abstract

A novel shear cell has been developed which allows for simultaneous measurements of the contact stresses and surface displacements during the sliding motion of a single particle against either another particle or a substrate representing a wall surface. Internal and wall friction behaviour of particles down to 500 μm in size were quantified by inducing relative displacements of contact surfaces over a range of 30 μm in steps of 0.1 μm, while measuring the resulting normal and shear forces at the contact to an accuracy of 0.01 N. Experiments were performed to determine the normal and tangential compliance of the test materials during the micro-slip of contact surfaces, leading to the gross sliding limit of friction. The results are compared with predictions based on the Theory of Elastic Contacts. Significant non-elastic behaviour is found to result during tangential loading of the contact region at high normal loads even when the normal load compliance is perfectly elastic. This result is believed to have important implications in the flow simulations of granular materials based on contact mechanics. Further tests were performed to quantify the normal load dependence of the internal and wall friction coefficients measured at the gross sliding limit. These measurements are interpreted using the Adhesion Model of Friction.