Distribution and formation mechanisms of maize kernel damage types during threshing based on discrete element modelling

• Threshing gap significantly affects kernel damage by altering threshing patterns. • Crown damage (32.89%) and broken kernels (28.89%) are predominant damage types. • DEM simulation revealed mechanism of each damage type under different parameters. • Optimal threshing occurs when gap matches ear diameter using rubbing pattern. Kernel mechanical damage during maize threshing accelerates mould development and quality degradation, particularly under suboptimal threshing parameters. This study investigated damage type distribution patterns and formation mechanisms through bench experiments and discrete element method (DEM) simulation. A single longitudinal axial-flow rasp bar threshing cylinder was operated at cylinder speeds of 300 to 500 r min⁻¹ and threshing gaps of 35 to 65 mm. Results demonstrated that threshing parameters significantly influenced kernel damage rates and type composition, with threshing gap as the primary determinant. When threshing gaps matched ear diameter, rubbing threshing predominated with minimal damage; gap deviations induced impact-compression threshing and severe kernel damage. DEM analysis suggested that excessive impact forces were the primary cause of kernel breakage, whilst prolonged ear residence time in the threshing chamber led to increased pericarp damage and kernel cracking. Model reliability was validated through comparison of axial distribution characteristics of threshed kernels between simulation and bench experiments (r > 0.985, p < 0.001; RMSE < 2.5%). This study provides differentiated parameter control strategies based on kernel damage distribution, enabling more targeted parameter control to minimise kernel damage.