The Simulation Of Granular Materiais's Strain Localization Based On Experiment And DEM And FEM By Macro-Mocro Two Scale Method

Soil particulate material's discreteness determines its specificity. Continuum theory can not truly reflect the mechanical properties and failure mechanism of soil material,but discrete element method can compensate for this defect. It can truly be effectively simulated soil conta ct force and displacement information of particulate material, but due to the large number of particulate material, and the huge number of components of interest led to a very large amount of calculation. Also, because of the classical continuum theory does not take into account the particulate material's rolling, so that part of the numerical calculation can not go on, it can not truly reflect the change in the displacement process of particulate material that is localized strain and strain softening. The Cosserat continuum theory introduces The rotational degree of freedom and couple stress,they are better able to corresponding to result of calculate value by discrete element method, can make up the classical continuum theory. In addition, Cosserat continuum theory also proposed a "scale parameter " concept,it has a huge advance in treating particulate material having a microstructure dimensions. In this paper,we combine Cosserat continuum theory and discrete element method and finite element method to study soil particulate material's numerical simulation based on two-scale in two-dimensional and three-dimensional. The main work is as follows:We choose a more reasonable model which consider particles scrolling mechanism by discrete element method, compile discrete element program to establish a two-dimensional biaxial compression test model by Fortran.calculates each particle contact force, contact torque and displacement and corner, and other information, then calculates the particulate material's stress and strain.A X-shaped shear zone can be clearly observed in effective strain diagram and body strain diagram of the model, this shows that the softening process of particulate material under pressure to consider rolling mechanism simulation of 2D strain is reasonable.We take a characterizing element as intermediate scale of micro to macro by two-scale theory.We get the characterizing element's stress and strain by particles'contact information,then get the dilatancy coefficient - effective strain curves and the coefficient of friction - Effective strain curve. Select the same parameters with discrete element model to simulate by finite element model, compare simulation results. Establish finite element model similar to the discrete element model to do finite element simulation. From the corner cloud, effective strain diagram and body strain diagram of finite element model,we can observe a shear zone the sameas the two-dimensional discrete element simulation. This shows that the discrete element-Cosserat continuum finite element analysis method for two-scale two-dimensional compression process particulate material strain softening question is valid.Use the obtained experimental data of sand sample by new plane strain gauges. By analyzing the big difference between the principal stress - axial strain figure of sand sample,we can get that shear band dominates in the compression. Select the appropriate characterization to obtain the sample's characterization yuan dilatancy coefficient-effective strain curves and the coefficient of friction - effective strain curve and establish a finite element calculation model to do FEM.Then compare to discrete element numerical calculation in two-dimensional space.Considering the practical engineering problems are in three-dimensional space,use discrete element method to compile program based on three-dimension by Fortran compiler, establish a biaxial compression test model, give displacement loading to it.Use the same method as the case of two-dimensional to analys every real-time particle's contact force, displacement and other information. Obtain a sample location map, Figure corner map, volumetric strain cloud map, effective strain cloud map and axial stress-strain curve of the sample. By analyzing we obtained that multiscale theory can combine the advantages of discrete element and Cosserat continuum theory, it can better solve problems that discrete element method can not.