The Calibration of Microscopic Parameters for the 3D Finite-Discrete Element Method.

The microscopic parameters in the numerical method have an important influence on the results and computational efficiency of the models. The existing calibration methods of microscopic parameters in the finite-discrete element method (FDEM) are based on two-dimensional (2D) FDEM model, and there is a lack of calibration methods for microscopic parameters suitable for three-dimensional (3D) FDEM model. Therefore, this paper proposes a fast and convenient calibration method for the microscopic parameters of the 3D FDEM model. First, a tangential contact force calculation algorithm based on the total normal force is proposed and verified by the slider model. Subsequently, assuming that the penalty parameter of the solid element is equal to the penalty parameter of the joint element, the relationship between the normal penalty parameter and the tangential penalty parameter, and the relationship between the normal penalty parameter and the Young's modulus are studied using several numerical models. Moreover, the tensile strength and crack propagation path of the Brazilian disc model under different fracture energy parameter combinations are studied, and the fracture energy parameters are calibrated. Then, the triaxial compression model under different confining pressures is used to calibrate the cohesion c and the internal friction angle φ. In addition, the effects of loading rate, mesh size and time step on the model strength and calculation time are considered, respectively. Finally, the numerical simulation of dynamic Brazilian splitting test is carried out to verify the reliability of the parameter calibration method proposed in this paper. Although the calibration method of microscopic parameters is not unique, the microscopic parameter calibration method has important reference significance and is conducive to the application of 3D FDEM model. Highlights: A tangential contact force calculation algorithm based on the total normal contact force is proposed and verified by the slider model. The tangential penalty parameter in the 3D FDEM model needs to be greater than the normal penalty parameter, and the threshold of the normal penalty parameter is 50 times Young 's modulus. The tensile strength of the Brazilian disc model always begins to converge when the fracture energy GII is equal to 10GI, and the crack propagation path is along the central diameter direction. [ABSTRACT FROM AUTHOR]