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Granular Matter (2015) 17:95110 DOI 10.1007/s10035-014-0526-0
ORIGINAL PAPER
Laboratory observations of frictional sliding of individual contacts in geologic materials
David M. Cole
Received: 6 June 2014 / Published online: 21 November 2014 Springer-Verlag Berlin Heidelberg (Outside the USA) 2014
Abstract This paper gives the results of grain-to-grain sliding friction experiments on several naturally occurring geologic materials and two manufactured materials. The materials include quartz sands with mean grain size dave ranging from 0.14 to 3mm, crushed and ball milled gneiss with dave = 14 20 mm, magnesite (limestone) with dave =
2 mm, and Caicos ooids with dave = 0.44mm. The reference
materials include manufactured glass beads (dave = 0.30
and 1.0mm) and spheres of a synthetic material (Delrin, dave = 19.05 and 5.08mm). The experiments involved nor
mal loads FN that ranged from 0.46 to 20N, depending on material, and the subsequent application of an increasing shear force at a loading rate of 1Ns1. This work contributes to the goal of providing high-delity contact models for use in discrete element simulations of naturally occur-ring granular materials. The results presented here provide a picture of shear force-displacement behavior up to and through the onset of macroscopic sliding. For natural materials with relatively rough surfaces, the coefcient of friction ranged from 0.1 to 0.9 at normal force levels FN < 10 N, but tended to converge to a narrower range (0.240.62) at higher FN levels. Grains with low surface roughness (glass beads, synthetic material and the 3-mm-diameter sand), on the other hand, exhibited a trend of decreasing with increasing FN , with terminal values in the range of 0.10.2 for 10 FN 20 N. This behavior is explained in terms of the
relationship between the normal force and the true area of contact. Additionally, observations of free sliding observed under cyclic shear loading are reported.
D. M. Cole (B)
Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, 72 Lyme Rd., Hanover, NH 03755, USA e-mail: [email protected]
Keywords Contact mechanics Friction Experiments
Granular media Coefcient of friction
1 Introduction
A number of problems dealing with the mechanics of granular geologic materials are being addressed with the discrete element modeling (DEM) method. Of particular interest to the present effort are engineering problems such as tire-soil...