Viscoelastoplastic bonded DEM–FEM simulation with hybrid calibration for optimized no-till rotary blades under wheat–maize rotation stubble conditions

Abstract Traditional rigid discrete element method (DEM) models cannot accurately describe the viscoelastoplastic deformation and fracture of wheat stubble under mechanical loading. To overcome this drawback, this study establishes a bonded viscoelastoplastic DEM framework by combining the Hertz-Mindlin with Bonding V2 model and JKR cohesion theory. Systematic laboratory tests were conducted to quantify the mechanical and interfacial properties of wheat stubble. The measured tensile strength, shear strength and shear modulus were 4.82 × 10 6 Pa, 4.72 × 10 6 Pa and 1.0 × 10 7 Pa, respectively. Collision, friction and pull-out tests were further performed to acquire interaction parameters for stubble-stubble, stubble-steel and stubble-soil contact pairs. A hybrid calibration approach integrating the steepest ascent method, Box-Behnken design and response surface methodology was adopted to optimize critical bonding parameters: critical normal stress of 3.10 × 10 10 Pa, critical tangential stress of 3.01 × 10 6 Pa and bond radius of 0.77 mm. The calibrated model achieved a relative error of merely 3.4% in shear force prediction. A coupled DEM-FEM model was validated via soil bin tests and field trials in Henan Province. In soil bin experiments, the relative errors of cutter shaft torque and seed-zone stubble clearance rate were 4.27% and 2.74%, with simulated values of 130.97 N m and 72.34% against measured data of 136.81 N m and 70.41%. Field tests produced an average cutter shaft torque of 167.32 N m and a seed-zone stubble clearance rate of 78.34%, showing good consistency with numerical and soil bin results. The proposed deformable stubble model effectively improves the prediction accuracy of DEM for no-tillage seeding scenarios. This work not only provides a theoretical basis and reliable technical tool for the structural optimization and energy-saving parameter design of conservation tillage machinery, but also offers practical solutions to residue-induced operational problems in the Huang-Huai-Hai agricultural region.