Calibration of physical and mechanical property parameters of broccoli seedling stalks

This study focuses on the problem of clamping damage during the mechanised transplanting of broccoli seedlings. Based on the physical and mechanical properties of broccoli seedlings, a bonding V2 particle adhesion model was constructed using the discrete element method to accurately simulate the mechanical behaviour of broccoli seedlings during mechanised transplanting. Six contact parameters and five adhesion parameters were selected using a Plackett-Burman(PB) experimental design, and the steepest ascent design was used to explore the effect of these parameters on the shear force and thus approximate the optimal parameter region. A quadratic model for the shear force and bonding parameters was established using a Box-Behnken Design(BBD) experiment, and the bonding parameters in the bonding V2 model were calibrated. The optimal bonding parameters determined were: normal and tangential contact stiffnesses of 2.014 × 109 N∙m− 3 and 1.00 × 109 N∙m− 3 respectively, critical normal and tangential stresses of 1.00 × 106 Pa, and a bond radius of 0.435 mm. Model validation was conducted using clamping deformation tests under practical clamping forces of 10–20 N on young ‘Yanxiu’ broccoli seedlings (30–40 days) with a stalk moisture content of 75.27–78.73% and a stalk diameter of 5.5 ± 0.05 mm. The relative errors between simulated and measured deformation were 8.57%, 11.63%, and 8.93% at clamping forces of 10, 15, and 20 N, respectively, supporting the rationality of the calibration method and parameter values within the validated conditions. The proposed workflow can be transferred to other vegetable seedlings; however, the calibrated parameter set is specific to the tested cultivar, moisture content, geometry, and loading range and should be recalibrated when these conditions change. The results provide a practical reference for designing clamping structures for mechanised transplanting of broccoli seedlings.