In the first part of this research, the interactions of a dual sideway-share subsurface tillage implement with soil were modeled by discrete element method (DEM) and eva‎luated in an indoor linear soil bin. In soil bin experiments, soil cutting resistance and soil disturbance characteristics resulting from the tillage tool operating at 0.25 m s-1 and 150 mm cutting depth, were measured. Spherical particles with Hertz-Mindlin contact model and parallel bond between particles were used to simulate agricultural soil aggregates and their cohesive behaviors. Sensitivity analysis was performed to identify the most sensitive parameters of the model that need to be calibrated. With sensitivity analyses, particle stiffness, bond properties and particle-particle coefficient of rolling friction were determined as the most important parameters for calibration. The angle of repose test was employed to calibrate the coefficient of rolling friction. The calibration of bond stiffness was performed through comparing the draft forces of a simple soil engaging tool simulated with DEM and those estimated with an analytical tillage modeling results using a trial-and-error method. The ratio of soil bin measured vertical force to draft force was used in calibration of the most sensitive model parameter, namely, particle shear modulus. Its calibrated value for a sandy clay loam soil was 50 MPa. The calibrated model was validated using the soil forces as well as the soil disturbance characteristics of the tool measured in the soil bin. When comparing the model to the experimental results, the relative error was -2.0% for the average draft force, 2.5% for the average vertical force, -7.7% for the average rupture distance, and 11.7% for the average disturbed area. Therefore, good correlations were achieved between the soil mechanical behaviors obtained by the experiments and the DEM simulations. It can be concluded that in DEM simulations of some tillage tools such as subsurface tillage implement, accurate predictions of the vertical forces as well as the draft forces, could be achieved by calibrating the particle shear modulus using the ratio of vertical force to the draft force applied to the tool. Therefore, in the second part of this research, the discrete element method simulations were used to determine the optimal tool geometry. Simulation of tillage tool-soil interactions provides opportunities to accelerate new equipment design and eva‎luate its performance. The dual bent blade subsurface tillage implement which its performance has been eva‎luated in the field, is a new conservation tillage tool deserving its soil cutting efficiency to be improved by optimizing its geometry using DEM modeling. In order to achieve this objective, the effect of share size (5.9, 7.6, 11.3, 16.8, 22.6 and 28.2 cm), rake angle (7.5°, 15°, 25°, 30°, 35° and 40°), tilt angle (10°, 20°, 25°, 30°, 35° and 40°), and shank rake angle (45°, 60°, 75°, 90° and 97.5°) of the tool plowing at 150 mm depth, on soil cutting forces and soil disturbance characteristics were investigated using the validated DEM model developed in part 1 of this study. Results showed that the draft and vertical forces increased with increasing share size, while the specific resistance (SR) decreased. With increasing share rake angle, the draft force, SR, upward vertical force and the degree of soil pulverization increased. The minimum SR of the tool was at the tilt angle of 20°.

عباس همت

علي اسحق بيگي، عليرضا باغبانان، غلامحسين شاهقلي

مرتضي صادقي، مرتضي نادري بلداجي، محمود بهينا