Wheat straw direct shear simulation using discrete element method of fibrous bonded model

A discrete element method (DEM) calibration for a flexible wheat straw model for simulating direct shear test of wheat straw was investigated. The calibration process uses DEM simulated Design of Experiment (DOE) of a three-point bending test, DEM parameters initialised from previous cantilever beam test, and uniaxial compression test of wheat straw. Wheat straw samples from physiologically matured Winter wheat straw (Triticum aestivum) material were used to estimate shape of a flexible wheat straw model and to obtain material testing data. Using the DEM simulated DOE of a three-point bending test, a regression meta-model was established between particle contact Young's modulus, and bond Young's modulus and Poisson's ratio. An optimisation procedure that minimised a global error relative to the test data was utilised to determine the DEM parameters of particle contact Young's modulus, bond Young's modulus, and Poisson's ratio. From the three-point bending test of wheat straw (length of 55 mm, a diameter of 2.81 mm, and a thickness of 0.35 mm), and DOE based optimisation procedure, the DEM predicted Young's modulus of flexible wheat straw at a percent relative error (RE) of 3.11% compared to test data. Using the optimised DEM parameters of the flexible wheat straw model, the direct shear box test was simulated using the flexible fibre DEM model, as a validation experiment. DEM successfully simulated the direct shear behaviour of wheat straw from the ASTM laboratory direct shear box test, predicting wheat straw angle of internal friction (RE of 1.67%) and apparent cohesion close to zero.