| In analyzing the problem of strain localization of granular materials,the discrete elementmethod and the Cosserat continuum finite element method are often used.In order to make full use of the advantages of the two methods,the two-scale simulation of the discrete element-Cosserat continuum model can be performed.In this process,we first need to determine the initial parameters required for the discrete element model,and then obtain Cosserat continuum parameters by characterizing the RVE-analysis.These parameters were introduced into the Cosserat continuum finite element model,and the comparative analysis of experimental,discrete element and finite element numerical results was comparative analyzed.A simple device was used to calibrate the coefficient of restitution between the particles and the boundary surface material,and the rationality of the device was verified by comparing the measurement results and the theoretical values of the collision recovery coefficient between the glass beads and the glass plate.The effects of drop height,particle size,and collision material on the restitution coefficient of glass beads were studied.Further,the method of measuring the coefficient of restitution was extended to rock and soil granular materials,and the restitution coefficients of coral sand and Fujian standard sand relative to glass plates,glass plates,and rubber membrane composites were measured.Then the friction coefficient between the discrete particles and the boundary surface material was measured.The boundary surface included the rubber membrane,filter paper,etc,while the particle materials involved were glass beads and Fujian standard sand.For particle aggregates with different particle sizes and regular shapes,a method is adopted in which a continuum material is used as a slider to slowly slide on the particles.The effects of the contact area,slider sliding speed,particle size,and particle compactness on the friction coefficient were analyzed.The friction coefficient between glass beads,Fujian standard sand and rubber membrane,and filter paper was measured,and the influence of irregular particle size on the friction coefficient was explored.Using the calibrated 2mm glass bead parameters,a 3-axis analog scale is simulated,and the simulation results are compared with the conventional triaxial test to verify the rationalityof the calibration parameters.Then,during the numerical simulation of the plane strain test,the influence of particle size effect on the simulation results was analyzed.Through the study of the size effect in the numerical simulation process,the influence of the particle size on the numerical simulation results is obtained.Using the rule of the axial stress peak with the particle size,the difference between the simulation result and the test result is the same as the test particle size.This verifies the rationality of the numerical simulation and the necessity of the size effect study.In this paper,the selection of representation elements in plane strain model is studied.According to the relationship between the parameters in the discrete element model,the Cosserat continuum parameters are derived,and the Cosserat continuum stress and strain tensor in the discrete particle model are solved,and then the law of the dilatancy coefficient and the friction coefficient with the bias strain is obtained.Using the obtained parameters,the finite element analysis of the plane strain test was performed.The results were compared with the results of the discrete element analysis and the experimental results to prove the effectiveness of the two-scale simulation.Finally,the 3D discrete element model was used to analyze the influence of the proportion of impurity particles incorporated into the slope on the slope stability,explore the effect of the length of the pile in the gravel pile model,the ratio of the particles' modulus of elasticity in the pile and the surrounding particles on the bearing capacity of the gravel pile... |
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