Modeling Shearing and Bending Behavior of Kiwifruit Branches Using the Discrete Element Method

Returning pruned branches into the field is a key procedure in kiwifruit cultivation. It utilizes discarded branches and aids in orchard management. Shearing and bending behaviors dominate the mechanized process of branch return; however, current research lacks appropriate modeling methods for these processes. In this study, we developed a discrete element method (DEM) model to simulate the shearing and bending behaviors of kiwifruit branches. Initially, laboratory experiments determined the shear strength and elastic modulus of branch samples to be 31.38 MPa and 1.21 GPa, respectively. An annular kiwifruit branch DEM model was constructed. A Plackett-Burman design test identified significant influencing factors: effective modulus of bond, bond cohesion, effective modulus between ball and wall, and the normal-to-shear stiffness ratio. Utilizing the response surface method, we derived relationships between DEM parameters and mechanical responses. Optimal parameter combinations were found: an effective modulus of bond at 2.2 x 109 Pa, bond cohesion at 2.56 x 108 Pa, effective modulus between ball and wall at 1.27 x 108 Pa, and a normal-to-shear stiffness ratio of 1.16. Finally, simulations of the shearing and bending processes were conducted. The optimal parameter combination was verified with a relative error of 4.5%. Displacement-force curves showed general consistency, indicating reliability in the modeling approach.