Analysis Of The Formation Of Shear Band In Granular Bodies Based On Particle Discrete Element Method

Granular materials are widely found in nature,and their physical properties are complex and varied.Using discrete element method to study its mechanical behavior has become a hot issue in scientific research nowadays.The formation and development of the shear band is one of the main realization forms of mechanical behavior of particulate matter.Studying the formation of shear bands can well reveal the intrinsic mechanism of action of macroscopic mechanical properties of granular materials.In order to get more detailed particle data information.This paper builds and develops a particle discrete element triaxial compression model based on the open source discrete element system.Combined with laboratory experiments,the mechanical behavior of the meso-level particles was statistically analyzed,and the deformation properties of the granular shear band at the macroscopic scale were revealed.The main conclusions of the study are as follows:(1)Numerical implementation methods for collision detection,interaction and kinematic variables between spherical particles are studied.The stress,displacement,and rotation between particles are described in detail.Based on the characteristics of rolling contact between particles,a discrete element numerical model which can control initial gradation and porosity is established by using a contact model considering particle rolling effect.(2)The generation and loading methods of the model are introduced in detail,and the influence of the mesoscopic parameters such as Poisson's ratio,friction angle and elastic modulus on the numerical model is analyzed.The numerical model was verified by laboratory tests with different gradations and porosity,and the test results were in good agreement.Numerical results show that: Under quasi-static loading conditions,various material parameters will have an important impact on the deformation and load bearing strength of the specimen.The uneven coefficient and porosity have a significant effect on the peak strength of sand.Sand with a dense and uneven coefficient of unevenness increases its shear strength.(3)From the point of view of the microscopic level.The large amount of data generated by discrete element numerical simulation is imported into the visualization software to analyze the generation and physical characteristics of the sample shear band.The three-dimensional force chain of the particle visually represents the internal mechanical structure of the sample during compression.The displacement vector clearly shows the internal particle migration route.The strain diagram clearly shows the formation of the shear band and its characteristic parameters,including position,thickness,inclination,etc.Based on these studies,statistical methods were used to analyze the displacement,velocity,rotation angle and coordination number of particles at different positions to study the difference in the motion law of the particles inside and outside the shear band.The effects of gradation and porosity on the motion parameters of the particles inside and outside the shear band were further analyzed.