Discrete Modeling Of The Creeping Characteristics Of Dense Granular Materials

Granular materials are commonly encountered in both nature and various industrial processes.Thoroughly understanding the complex flow and mechanical behavior of granular materials is obviously meaningful to the design,optimization and scale-up of the equipment for handling granular materials.It has been reported that the mechanical response of dense granular materials presents remarkable spatial correlations,designated by the factor that the rheological behavior of local region can be significantly influenced by the mechanical disturbance originated from other region.How to characterize and reflect such spatial correlation is exactly the kernel of various rheological constitutive laws of dense granular materials reported in literature.In this work the mechanical failure processes of granular material under different shear loading conditions are simulated through performing two dimensional Discrete Element Method(DEM)simulations.The possible mechanisms of the influences of mechanical disturbance on the failure process are then discussed.The main contents and conclusions of this work are as follow:(1)In chapter 2,the mechanical responses of granular material sheared by a constantly moving wall are simulated.The simulation results indicate that particles outside the shear band present creeping movement parallel to the shear direction rather than in absolute stagnant state.The classical μ(I)model can describe the effective frictional coefficient of granular particles in the rapid flowing zone.Nevertheless,for granular particles in the creeping zone,their effective frictional coefficients are not solely decided by the inertial number I.analyses indicate that,by including the influence of particle fluctuation motion,the corrected μ(I)model can successfully describe the effective frictional coefficient of granular materials in different flowing zones.(2)In chapter 3,the stick-slip phenomena are investigated.The stick-slip motion is realized through moving the free end of virtual spring which another end is attached to the upper shear wall.The simulation results show that the transition from stick state to slip state is accomplished by the strengthening of heterogeneous stress distribution,the decrease of contact number and the weakening of the mechanical support from the weak contacts to strong contacts.In stick stage,imposing mechanical disturbance will trigger the occurrence of slip event.The awaiting time of slip event increases with the decreases of the amplitude and frequency of the disturbance.Analyses reveal that the creep motion of particles induced by the mechanical disturbance,which subsequently leads to the weakening of the geometrical support from the weak contacts to strong contacts,might be responsible for the advance of slip event.(3)In chapter 4,the stick-slip phenomena occurred inside granular material are modeled through simulating the motion of an inside intruder which is dragged by a virtual spring.It is found that,with the stretching of the spring,notable stress concentration appears in the region in front of the intruder.At the same time,the geometrical stability of the contact network in front of the intruder decreases.These two subsequently lead to the occurrence of slip event.The occurrence of slip event can be promoted by impose mechanical disturbance on the intruder.Such result can be ascribed to the promotion of the formation of strong force chain and the weakening of the geometrical support from the weak contacts to strong contacts.