The development of a new micro-mechanical inter-particle loading apparatus

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Original languageEnglish
Journal / PublicationGeotechnical Testing Journal
Issue number6
Online published2014
Publication statusPublished - Nov 2014


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, 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.

Research Area(s)

  • Bearing balls, Calibration, Experimental micro-mechanics, Inter-particle coefficient of friction, Linear bearing, Linear stepping-motor, Nonconforming surfaces, Quartz particles, Stick-slip, Stiffness