Goniometer for determining the interparticles friction

Abstract

Tests for measuring friction between partícles were carriede out as basic research to throw light on the internal friction mechanism of granular materials. For this purpose a new apparatus, the friction goniometer, was developed.  With this apparatus, used to measure directly the friction angle at the contact between two particles a constant intensity force is applied, whose obliquity angle is made to increase up to the occurrence of sliding between particles. The maximum value of this obliquity gives the friction angle.  Contact surfaces of particles are tested in their natural form, without any grinding operation to make them flat. The apparatus was designed to measure the friction angle at a given particles only along one direction of this contact; therefore it does not allow easy determination of the anisotropy of a contact as concerns friction. Thus this is a unidirectional goniometer. The main causes for systematic errors are analysed, and ways to correct them are presented. Advantages of multidirectional goniometer are pointed out, in what concerns both avoidance of systematic errors and studies of anisotropic frictions. Results are given of tests on particles of quartziferous gravei, crushed limestone, and gabbrodioritic crushed stone. Comments are made on the results, and further research is referred to.