Elastic-plastic Deformable Contact Model Of DEM Based On Nano-indentation Test

The granular materials is one of the most common material forms in daily life, itcan’t be studied on by the traditional continuum theories because of its own uniquecharacteristics. Discrete element method is an effective method to deal with thenumerical calculation of the non-continuum material. Compared with finite elementmethod it has irreplaceable advantages on analyzing motion state of a large number ofparticles. The contact model is the most important part of the discrete element method,Motion state of particle is depended on the contact force calculated by the contactmodel. Plastic deformation of particles is inevitable in the real processes, due to thelarge contact pressure. However, it is usually not considered in most of the existingdiscrete element method (DEM) analysis.Firstly, the load-displacement curves obtained by results of FEM simulations ofthe nano-indentation tests is fitted by appropriate models. The load and unload fittingparameters are affected by many factors such as the angle of the indenter and thefriction. The results show that the frictions between the indenter and materials have littleor no influence on the value of the fitting parameters but the fitting parameters aredirectly determined by the angle of the indenter.Secondly, the contact process between polygon particles is studied under thequasi-static assumption. The loading and unloading stiffness is given to every vertex ofthe polygon particles which is calculated by the load-displacement curves. The contactforce among the granular materials can be got from the stiffness and the overlapbetween particles. Plastic deformation and residual deformation during the contactprocess can be described by the variation of the vertices’ radius value.Finally, the software of discrete element method was programed by using the Clanguage and Java language. The collision course between the polygon particle withinitial velocity and the rigid wall is simulated by discrete element method and finiteelement method. Compared with the linear viscoelastic models, the results indicated thatmore accurate contact force and the contact time can be obtained with this elastic-plasticmodel, meanwhile elastic-plastic and residual deformation of the particles can bepresented effectively. The simulation model is simple and the computational cost isreduced by this model compared to finite element method.