Low-damage cutting mechanism and optimisation experiments of operating parameters of Caragana korshinskii Kom. Stems based on discrete element method

The unclear dynamic coupling mechanisms among operational parameters during Caragana korshinskii Kom. (CK) harvesting operations lead to suboptimal stubble flatness of cut stems, impairing perennial CK regrowth capacity and causing significant biomass resource waste. This necessitates theoretical exploration of low-damage cutting mechanics for CK stems to optimize harvesting parameters. We established a mathematical model for cutting stems with a circular cutter. Through theoretical analysis, it was determined that the feed speed (V_f), rotational speed (R_ω), and cutting angle (θ_c) of the cutter are important factors affecting the CK stem cross-section flatness (q_c) after CK cutting. Numerical simulation experiment results indicated that q_c exhibits a ‘low–high-low’ characteristic as V_f, R_ω, and θ_c increase. When the values of these parameters are small, the bending angle of the stem (α) is large, the quantity of high-speed particles (β) is high, the stem cross-section manifests defects including bumps, depressions, and splits. Concurrently, the number of broken bonds in the stem model (M) reached higher values, leading to a reduction in q_c. As the values of these parameters increase, the cutter cutting trajectory becomes smoother, α and β decrease, and these characteristics reduce the cutter’s disturbance and damage to the stem, causing M to decrease and q_c to increase. When the parameter values continue to increase, α, β, and M increase, and q_c decreases. The optimum operating parameters were determined using the Box-Behnken design test, when V_f = 3.14 km·h⁻¹, R_ω = 995.92 r·min⁻¹, and θ_c = 10.0°, α and β decreased by 1.62 %–30.31 % and 3.85 %–37.73 %, M decreased by 1.08 %–15.10 %, and q_c increased by 0.40 %–17.20 %. The field experiments verified the results of the numerical simulation, in which the residual stubble levelling was 91.2 %, with an error of 1.5 % compared to the results of numerical simulation experiments. Simultaneously, the missed cutting rate was 7.5 %, which met the agronomic requirements for CK harvesting. This work advances stem-cutter interaction theory and informs high-efficiency CK harvester development.