Objective To reveal the influence mechanism of soil moisture content on the mobility performance of agricultural tracked chassis, and clarify the mutation threshold of critical performance indexes.

Method This study established a soil-track interaction model via discrete element method-multibody dynamics (DEM-MBD) coupling simulation using a generic agricultural tracked chassis. Soil-DEM parameters were calibrated using an pile angle test. Simulations were conducted for soils with moisture contents (ω) of 5%, 10%, 15%, and 20% to analyze the dynamic responses of vehicle speed, sinkage, axial offset displacement, traction, drive torque and attitude angles (pitch angle and roll angle) during traversal.

Result The chassis traveled stably on low-moisture (≤15%) surfaces, with an average speed of 0.85 to 0.88 m·s⁻¹ and a coefficient of variation (CV) ≤ 1.09%; At higher moisture content (20%), speed decayed to 0.61 m·s⁻¹ and the CV rose sharply to 7.90%, with 15% moisture content identified as the stability threshold. For moisture contents from 5% to 15%, steady-state sinkage increased gradually from 70 mm to 150 mm; for 15% to 20% it rose sharply to 370 mm. Axial offset displacement remained < 200 mm when moisture was ≤ 10%, at 15% it spiked, and at 20% excessive sinkage caused the offset to drop to 118 mm. Traction decreased linearly with increasing moisture content, while drive torque increased nonlinearly. High-moisture soils exhibited rheological softening and enhanced slippage, requiring larger torque to overcome resistance. Pitch angle and roll angel responded with a “disturbance-equilibrium-restabilization” pattern, with 15% marking an attitude-transition threshold and 20% corresponding to narrowed attitude fluctuations.

Conclusion This study quantitatively analyzes the critical threshold of soil moisture content and the nonlinear response mechanism of undercarriage performance, providing a theoretical support for the adaptive design of tracked undercarriages and the optimization of field operations.