Three-dimensional discrete element modelling of tillage: Determination of a suitable contact model and parameters for a cohesionless soil

Accurate modelling of soil-implement interaction is vital to optimise the design of tillage implements. Discrete element modelling (DEM) is a numerical method used for modelling the mechanical behaviour of granular materials. When DEM is used for tillage the soil is assumed to consist of distinct particles with the interactions between the particles controlled by contact models that are governed by physical laws. In previous three-dimensional (3D) DEM tillage studies the soil particles were assumed as having elastic contacts and the plastic deformation behaviour of the soil particles was not taken into account. Using EDEM software, a non-linear elastic contact model was compared with a linear hysteretic spring contact model that considers the plasticity of the soil. The DEM parameters required to run the simulations were determined from angle of repose and penetration tests, matching the simulation results to test results using a modelled spherical particle with radii of 10 mm. The simulation results of both the non-linear elastic and linear hysteretic spring (plastic) contact models were compared with experimental results from a sweep tillage tool. An improved correlation was obtained between the measured draft and vertical force results using the linear hysteretic spring (plastic) contact model. Further simulations using the linear hysteretic spring (plastic) model showed there was a quadratically increasing trend with particle size from 4 to 10 mm for the parameters of coefficient of restitution of soil-soil, friction of soil-soil and integration time step.