Three-dimensional discrete element modelling (DEM) of tillage: Accounting for soil cohesion and adhesion

• Cohesion and adhesion can be directly added to the normal contact forces in HSCM.
• The proposed model has good potential to accurately model tillage forces.
• Different soil and operating conditions can also be modelled using proposed model.

Recent studies have shown that the discrete element modelling (DEM) can effectively be used to model the soil-tool interaction if both an appropriate contact model and DEM parameters are used. Ucgul, M., Fielke J.M and Saunders, C. (2014a) Biosystems Engineering. 121: 105–117 showed that hysteretic spring contact model (HSCM) can give accurate predictions of draft and vertical forces for a range of sweep tillage tool geometries operating in a cohesionless soil. In this study a linear adhesion/cohesion model was integrated with the HSCM to model the cohesive behaviour of soil and its interaction with a tillage tool. The proposed contact model was validated with the direct shear tests performed and further validation was achieved via DEM simulation of the interaction between soil and tillage tool tests. The results showed that the suggested contact model can be used to predict both tillage draft and vertical tillage forces for varying speed, operating depth, moisture content and compaction levels. The results also showed that the DEM parameters determined in our earlier paper can be directly used in the suggested model without further re-calibration. It was observed that the soil bulk density has a significant effect on the predicted tillage forces and when the measured wet bulk density was used in the simulations a good correlation with measured forces was able to be achieved. Thus, the method presented has good potential to accurately model tillage forces in a range of soil and operating conditions.