Discrete element modeling and physical experiment research on the biomechanical properties of cotton stalk

The biomechanical properties of cotton stalk (CS) play an important role in the development of uprooting, crushing, and processing machinery, as well as in the comprehensive utilization of biomass resources. Establishing a discrete element model that can accurately reflect the biomechanical properties of CS can serve as a basis for the simulation of related operating machinery, including uprooting and processing machinery. In this study, a discrete element model of CS was developed using a combination of discrete element modeling and mechanical experimental tests. Eleven initial factors (including six contact and five bonding parameters) were screened using the Plackett–Burman design. The effects of these factors on the compression force–deformation (F–x) curve were investigated using the steepest climb test design. A second-order regression model of the compressive peak force (FC) and bonding parameters was established using the central composite design method, and the bonding parameters of the CS model were calibrated. Based on the results, the optimal combination of the bonding parameters was determined: a normal stiffness per unit area of 9.72 × 109 N·m−3, shear stiffness per unit area of 9.38 × 109 N·m−3, critical normal stress of 8.43 × 109 Pa, and bonded disc radius of 0.66 mm. Compared with the compressive experimental results, the deviation of FC was only 1.1 %, the F–x curve trend was consistent, and the error in the slope of the fitted equation for the elastic deformation stage was 0.7 %. Compared with the bending experimental results, the error in the peak bending force was 2.53 %. The results showed that the established discrete element model can be used to accurately simulate the compression of CS and that the method of calibrating the parameters for accuracy is reasonable. These results are important for studying the biomechanical properties of CS and optimizing the mechanisms whereby cotton stalks are uprooted and crushed.