Calibration of the discrete element method using an annular ring shear tester

The discrete element method (DEM) has become the method of choice to model bulk material flow behaviour. DEM models can be accurate and of value to industry only if the parameter values are carefully calibrated. Various calibration techniques and experiments exist such as the angle of repose, draw down tests and direct shear tests. The annular ring shear tester (Schulze tester) is often used to determine the flow properties of powders and fine granular materials. In this paper it was used to calibrate the DEM parameters for relatively large corn grains (9 mm in size). Two custom built shear cells were used for this purpose. One cell was manufactured from steel with a major and minor diameter of 260 mm and 138 mm respectively and the other cell was manufactured from clear acrylic with a major and minor diameter of 240 mm and 110 mm respectively. The particle-wall coefficient of friction was changed in the steel cell by adding sandpaper to the cylindrical walls. The aim of this was to eliminate or reduce particle-wall sliding which is an unknown in the DEM model. The results showed that DEM accurately modelled the particle-wall interface with and without sandpaper. The transparent cell and PIV was used to observe the movement of the particles during shear and to compare the performance of the shape approximations, namely multi-sphere particles (where the number of spheres per particle was varied) and faceted particles. Results showed no significant difference in the bulk shear behaviour of the various shapes tested.