Discrete Element Simulations Of The Intensity And Sound Velocity Of The Shear Particle System Under Different Contact Models

During the sheared process of a granular system,the change of the shear stress or the perturbations generated by the acoustic wave will cause instability.The solid-liquid transformation is similar to the triggering of earthquake caused by the instability of the fault gouge.The study on the variation in shear stress and acoustic propagation properties of quasi-static granular system is of great significance for understanding the formations of earthquake and avalanche.In this paper,the properties of shear curves under different contact models and the change of sound velocity are studied by the discrete element method,in order to provide a reference for understanding earthquake and avalanche from the point of view of granular matter.Different contact models have significant influences on the shear curves,and this paper focuses on the rolling resistance model between particles.On the one hand,the normal and tangential contact models are relatively mature,on the other hand,the commonly used rolling resistance models are various and some of them are of contradictory,how to introduce the rolling resistance correctly is an unresolved problem.In this thesis,the rolling resistance model for circular particles is generalized to simulate non-circular particle system,and compared the simulation results with five rolling resistance models commonly used in other literatures.After the analysis of the results,the suitable rolling resistance model is identified by the rate independence,and the rolling velocity of the model satisfies the objectivity.The shear and dilatancy curves at different rates are coincident,and the simulation results under different normal stresses with different friction coefficients are consistent with experiments.The rolling resistance given in this paper is also appropriate for different normal and tangential contact models.On the basis of the correct contact model,the propagation of sound waves in the simple shear flow of spherical particles is simulated.The shear and compressional waveforms are obtained,and the relationship between acoustic velocity and shear displacement are calculated.The simulation results show that the shear band is different from the fluid,and the shear wave can pass through it,furthermore,the velocity is proportional to the 1/6 power of the normal stress.The simulation results are consistent with the experiments.The results of this paper are helpful to understand the physical mechanisms of natural disasters such as earthquake and avalanche,which are triggered by the instabilities because of the variation in shear strength or acoustic perturbation.