Analysis of modern methods for determining the dynamic friction of bulk materials

Abstract

The coefficient of dynamic friction is investigated in widespread gravitational flows of granular materials of numerous technological processes. The calculation of dynamic friction is necessary in the study of shear flows, the behavior of the sediment layer on an inclined plane, tracking the sticking motion, damping friction in structural dynamics and sliding resistance. The friction coefficients of particles against each other depends on many factors (a set of physical and mechanical properties of particles, chemical and fractional composition, the presence of a lubricant, oxide films, moisture and other conditions, such as volume, angle and height of falling particles), each of which separately difficult to count. The experimental determinations of the value of the coefficient of internal friction during pressing are the most reliable; however, such methods are not applicable in the course of analyzing mixtures in the mining and metallurgical industries due to the fact that bulk materials of this type are characterized by gross porosity and are prone to breaking during similar experiments. To obtain reliable results of mathematical and computer simulations, there is a need to evaluate the mechanics of flow of granular materials or bulk solids. There is a shortage of ways to predict these patterns, that require understanding and conducting extensive basic research. At present, several models are used to describe the connected state of materials (soils, sands, granules and powders): soil mechanics, hydromechanical (continuum mechanics), continuity hypothesis (phenomenological model). All existing methods are based on the average value of the characteristics of a large number of particles and can not be used to describe models with high fractional void volume, and as a result, do not describe each discrete particle in the composition of the flow of bulk materials. This article provides an overview of existing methods for assessing the dynamic friction of solids, their applicability in various situations, as well as the development trends of this scientific field.