Distinct element analysis of attrition of granular solids under shear deformation

Abstract

The attrition of spherical particles in a periodic cell under shear straining is analysed by distinct element method (DEM). The damage mechanisms of surface wear and fragmentation are under consideration. The side crushing strength (SCS) of single particles is used as the criterion for fragmentation. For surface damage, the abrasive wear by the formation of lateral cracks during shearing is calculated using a model of chipping for the semi-brittle failure mode. The contributions to attrition by surface wear and particle fragmentation are therefore decoupled and quantified. The simulation results are then compared with the experimental data reported previously. The contribution of fragmentation to the overall attrition is found to be dominant over the full range of strains tested in this work in agreement with the experimental data. The extent of attrition predicted by the simulations compares generally well with the experimental data except at the lowest normal stress and at high shear strains. For the former, the reason for the poor agreement is unclear. For the latter, the difference is attributed to the presence of fragments and debris as they affect the contact force distribution and this feature has not been simulated. The parametric sensitivity analyses indicate that the simulation results are sensitive to particle properties such as Young's modulus and the coefficient of friction. Therefore, careful material characterisation is necessary in order to get reliable predictions. The effect of the shear strain rate on particle breakage has also been examined by simulation. The results indicate that the rate of attrition is not sensitive to strain rates normally used for shear cell tests, i.e., of order of 1 s - 1 .