A Study On Force Propagation And Tuning Mechanical Response In Static Granular Materials

Granular material usually exhibits some essential features,which present fundamental difficulties and great challenges in quantitatively modeling and simulating their macroscopic behaviors.Among these problems,the stress propagation in granular material under an external localized load has attracted much attention in recent years.In a granular material,the forces between internal particles,transmitted from one particle to the next via their contacts,may commonly form an inhomogeneous contact network at a meso-scopic scale,which carries most of external loads by way of force chains,while whole system may exhibit some localized deformation features at a macroscopic scale.This discrete nature commonly induces the occurrence of anisotropic force chains and spatially inhomogeneous stress distribution,which may lead to a difficult to describe mechanical properties of granular material using conventional continuum theories.The mechanical response of granular system under local external loading is a fundamental problem in researching field of granular materials.The macroscopic mechanical response of the particulate matter is mainly determined by contact force and contact network on the microscopic scale.Therefore,in order to understand the macroscopic mechanical response of granular material,it is a very important and effective approach to study and analyze the contact force propagation.In this paper,the discrete element method is used to study the stress transmission and mechanical response characteristics of granular material under the localized concentrated force.At first,a 2D composite granular layers composed by particles with variable stiffness is proposed,and the effect of stiffness ratio between component particles on mechanical response is mainly considered.The results show that the decrease of stiffness ratio broadens the linear range of mechanical response and enhances the elasticity of the response in a composite granular system,showing a role similar with the friction in a monodisperse granular packings.Furthermore,a phase diagram for the crossover between a single-peaked and a double-peaked response is proposed,in which the critical stiffness ratio corresponding to the occurrence of the crossover decreases with the magnitude of external loading and increases with the friction.Finally,the microscopic mechanism of the crossover of the response is further discussed based on changes in contact network and force network.Secondly,a variety of particle composite models were established on the basis of the two composite models.The main factors influencing the mechanical response in the composite model were the difference in the stiffness between the two kinds of particles.It meant the greater the difference in stiffness,the greater the impact of chain transfer.The influence of the disorder degree of the particles was also studied,and the disorder degree would be affected by the linear range and the critical load of the system.They were all decreased with the increasing of the degree of disorder.Finally,an new approach by adding hard particle channel to tune the mechanical response of granular slab applied by an external loading is put forward,and the dependence of tunable range for the external loading and effective region placing the channel on the channel mode,position and its comprising granular layers is mainly considered.From sets of numerical results,we find that the existence of hard particle channel can lead to a transition of the response into a single-peaked feature when the response of corresponding monodisperes system is double-peaked,but it works just when the position of this channel locates within a central small range of total layer depth.Outside this range,the variation of the response induced by the existence of the hard particle channel is not qualitative but just quantitative.