Calibration of discrete element parameters in wheat-corn farming straw mixed soil returning mode

In response to protective tillage model of straw mixed soil returning to the fields in the Jianghuai and Huanghuai regions, where wheat-corn are harvested twice a year, lack of accurate material contact parameters in wheat straw-soil mixed seedbed hinders research on interaction between key components, seeds, fertilizers, and mixed seedbeds in the precision sowing process of mechanized corn, thereby restricting optimization and improvement of machinery．A combination of physics and EDEM discrete element method was adopted to study interaction between non continuous wheat straw and soil mixture．Bonding V2 bonding model was used to build flexible wheat straw segments "elemental particles", and the Hertz-Mindlin with JKR model was selected to calibrate parameters of soil with certain humidity．Firstly, stacking angle of wheat straw and soil seedbed mixture was taken as response value by using a circular bucket to lift．Plackett-Burman screening test and steepest climbing test were used to sort and shorten optimal range of significant influencing factors from large to small, respectively．A second-order regression model for significant influencing factors and stacking angle was constructed using Box-Behnken experiments．Response surface analysis was performed on interaction terms of significant factors．Design-Expert software was used to optimize model and measured stacking angle was 39.94 ° as the target response value．Results showed that surface energy of soil JKR was 0.500, dynamic friction coefficient of soil-straw was 0.0658, surface energy of soil-straw JKR was 0.262, and dynamic friction coefficient of soil-soil was 0.155, simulation validation error was 1.08%, indicating reliability of calibrated contact model parameters．This study could provide a reference and theoretical basis for study of interaction between mixed seedbeds and precision seeding equipment under wheat jade conservation tillage model．