Calibration of rototilled soil block discrete element parameters after rotary tillage in rape planting by machinery

This study sought to construct and empirically validate a discrete element method (DEM) particle model representing post-tillage soil blocks. This model was developed to facilitate a detailed examination of granular movement and contact mechanics during the shaping process of planting chambers for rape plants. The research specifically targeted the sticky, cohesive soil prevalent in rice paddy fields of the middle and lower Yangtze River region. Simulations were conducted using EDEM software to improve the accuracy with which soil-tool interactions are predicted for the design and optimization of mechanical transplanters. The physical and bonding parameters of the sticky soil were calibrated using the Hertz-Mindlin with Johnson-Kendall-Roberts (JKR) contact model and Hertz-Mindlin with Bonding contact model. A particle replacement method was adopted to create a discrete element model of cohesive soil aggregates with different shapes and sizes after rotary tillage. The accumulation angle of soil aggregates was used as the evaluation index in both the simulation and physical experiments. Design-Expert software was used to design a four-factor, three-level simulation experiment to identify the optimal parameter combinations for the physical and mechanical properties of the sticky soil and the JKR contact model, which comprised a soil-soil static friction coefficient of 0.32, soil-soil rolling friction coefficient of 0.10, soil-steel static friction coefficient of 0.51, and surface energy of soil for the JKR model of 5.50 J/m². Next, the steepest climbing test and Box-Behnken orthogonal combination test were then used to narrow down the range of values for the significant factors and identify the optimal parameter combinations for the bonding contact model parameters, which included a bonding bond normal contact stiffness of 2.1×10⁶ N/m, a bonding bond tangential contact stiffness of 2.2×10⁶ N/m, a normal ultimate stress of 0.55 MPa, a tangential ultimate stress of 0.55 MPa, and a bonding radius of 12 mm. Field experiments were conducted using a flat box device to measure the soil evenness and firmness after ridge formation and compaction by a rotary tiller. The results of these experiments were compared with the discrete element simulation optimization results. The relative errors between the field test results and the simulation test results for soil flatness and compaction were 10.7% and 9.8%, respectively, which indicated good accuracy of the parameters calibrated and optimized by EDEM discrete element simulation software. Overall, this research can provide a reference for understanding the working mechanism and optimizing the parameters of soil touching components in rape transplanting equipment.