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Volume 37, Issue 6 (November 2014)
The Development of a New Micro-Mechanical Inter-Particle Loading Apparatus
(Received 13 October 2012; accepted 22 August 2014)
Published Online: 13 October 2014
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The inter-particle coefficient of friction comprises an essential input parameter in computer codes that utilize the discrete element method. This paper describes the main features of a custom-built apparatus of a new generation, capable of performing inter-particle shearing tests at very small displacements on the order of tens to hundreds of microns and measuring the frictional forces developed at the contacts of coarse-grained particles of sand to gravel size. Linear, micro-stepping motors are used for the inter-particle shearing tests of a displacement-controlled type and the application of the vertical confinement of a force-controlled type at the particle contacts. The apparatus is designed to work at very small confining forces, in general between 1 and 20 N, and utilizes a system of bearings of small friction, which can be calibrated following simple procedures. The experiments are controlled and monitored through a computer code developed for the apparatus. The signal conditioning and data-logging systems were optimized to give the minimum environmental and electrical noise in the experimental data. The particles tested must have a relatively convex shape and be fairly symmetrical about the axis of shearing to avoid significant lateral forces in the out-of-plane horizontal direction during sliding, and, in general, the size of particles is limited from about 0.50 to 5.0 mm. Tests on reference particles composed of chrome steel balls and quartz particles demonstrated high repeatability of the results and agreement with the literature data. The experimentally derived horizontal force–displacement data showed that the stiffness of the apparatus is sufficiently high to prevent significant stick-slip phenomena, allowing a stable sliding.
Lecturer, School of Civil and Environmental Engineering, University of New South Wales, Sydney,
Chair Professor, Dept. of Civil and Architectural Engineering, City Univ. of Hong Kong, Hong Kong,
Stock #: GTJ20120187
Title The Development of a New Micro-Mechanical Inter-Particle Loading Apparatus