Test Apparatus for Determining the Particle-to-Particle Friction Coefficient

Granular materials usually require the design of specialised equipment for their processing and transport. Nowadays, equipment design increasingly relies on modelling techniques to support decision-making during the design process. The Discrete Element Method (DEM) is a numerical technique that enables the prediction of forces and displacements acting on individual particles. The design of ship loaders, dumpers, screw conveyors, conveyor belts, moving floors, bucket elevators, truck feeders, hoppers, and silos can all benefit from DEM-based predictions of particle behaviour. To develop DEM models able to accurately predict the particle behaviour, it is essential to characterise the material by determining its physical and mechanical properties. Key parameters include particle density, elastic modulus, Poisson’s ratio, particle-to-wall friction, and particle-to-particle friction. In this research, a methodology is proposed for determining the particle-to-particle friction coefficient. For this purpose, a test apparatus was designed and constructed to perform direct measurements of sliding angles. The proposed method yielded an average particle-to-particle friction coefficient of μ = 0.62, based on twelve independent sliding-angle tests. The measurements showed an overall relative standard deviation of 3.4%, indicating good repeatability and demonstrating that the developed apparatus provides reliable and consistent friction values for granular particles. The primary aim of the study was to validate the test method. Hand-made clay samples were produced, arranging the particles in different configurations and placing them in various orientations on the apparatus. The results confirm that the proposed method is suitable for determining representative particle-scale friction parameters, offering a simple and repeatable approach that can support DEM calibration and enhance the predictive capability of granular flow simulations.