Discrete element modelling and simulation parameters calibration for the compacted straw cube

The compacted straw cube (CSC) is the structural unit of a rectangular straw bale. A rectangular straw bale can be regarded as an ordered assembly of several CSCs constrained by strings. Straw bale is the object of mechanical operation in the straw collection, storage, management, and terminal utilisation. As a basis for studying the mechanics of rectangular straw bales, it remains a challenge to establish the CSC discrete element model incorporating the elastic, plastic, and viscous mechanical characteristics of the flexible straw and calibrate its simulation parameters. An original method of CSC discrete element modelling and simulation parameters calibration based on EDEM software was proposed. The CSC model was developed by performing virtual uniaxial compression tests with thousands of flexible straw stems using Edinburgh elasto-plastic adhesion (EEPA) as the contact model between straw stems. With compressive stress σ10 as the response value, the discrete element parameters of the CSC model were determined by the Plackett-Burman design test, the steepest climb test, and the Box-Behnken design test. The results showed that the relative error of the simulated compressive stresses σ10 was 1.04% for the 120 mm thickness of CSC. The relative errors of the CSC with 180 and 240 mm thicknesses were 3.89% and 2.6%, respectively, which validated that the model and parameters were reliable. The proposed method provides a new perspective for analysing the interaction mechanism between straw bales and mechanical components, which is significant for the development of straw management and utilisation equipment.