Investigation of the predictability of mouldboard plough draught from soil mechanical strength (cone index vs. shear strength) using finite element modelling

Abstract

Prediction models for draught of tillage implements using soil variables which can be readily measured in the field are important tools in agricultural machinery management. In our previous study, a regression model for draught of a cylindrical mouldboard plough as a function of soil water content, bulk density, ploughing depth and speed was developed using a finite element (FEM) model. This study aims to investigate whether the soil physical properties could be replaced by soil strength variables including cone index (CI) or shear strength (SS) measured by cone penetrometer and shear vane, respectively. Cone penetration and shear vane tests were simulated using FEM in the soils for which the mouldboard plough draught was obtained from the mouldboard plough-soil interaction model. A 0.3 m ploughing layer was simulated either homogeneous or non-homogeneous. CI and SS, averaged over the ploughing layer, were used as soil strength variables. The best model for mouldboard draught was obtained as a function of SS, ploughing depth and speed with R2 = 0.87 and RMSE = 0.79 kN. Validation of the model with a set of experimental data reported in the literature showed that the predicted draught force lies within bounds of ± 18 % of the measured values with R2 of 0.84. The draught model could be employed with a shear vane or a combined vane-cone instrument to predict the mouldboard plough draught.