Spherocylinder-Based Discrete Element Modeling and Dense Compression Simulation of Rice Straw in a Baler

Producing high-density rice straw bales requires a model that captures the anisotropic deformation and breakage of fresh straw during compression. We therefore developed and calibrated a spherocylinder-based discrete element model for rice straw baling. The model represents hollow elliptical cross-sections, distinct stem and node structures, and anisotropic bonding, and its mechanical and breakage responses were evaluated before its application to compression baling device optimization. Calibration via single-factor, Plackett–Burman, steepest ascent, and Box–Behnken experiments using the angle of repose as the target identifies three key parameters: straw–straw rolling friction (0.593), straw–steel rolling friction (0.188), and node Poisson’s ratio (0.411). The calibrated model reproduced the measured angle of repose with a relative difference of 0.39% and reproduced the compression and shear responses within 10% error. Compared with a multi-sphere model, the spherocylinder model reduces the particle count by 90.25%, simulation time by 72.52%, and memory usage by 89.83%. Adams–EDEM co-simulation reproduced the progressive deformation and localized breakage observed during baling, without excessive pulverization. Simulations across different tapered opening angles identified a balanced density–torque configuration, which was validated by field trials with a relative density error of 1.23%. These results demonstrate the model’s accuracy, efficiency, and practicality for simulating rice straw in compression molding machinery.