Dem Investigation Of Influence Of Particle Breakage And Shape On The Mechanical Behaviors Of Granular Materials

Granular materials are composed of a large amount of discrete particles,and exist widely in many fields,such as geological disaster,geotechnical engineering,chemical engineering,environmental engineering and transportation etc.The macroscopic mechanical behavior of granular materials depends on microscopic factors,such as particle breakage,shape,size distribution,arrangement and material properties etc.The discrete element method(DEM)establishs the numerical model based on the discrete feature of granular materials.DEM treats granular materials as assemblies of discrete particle elements,and provides an effective approach to research mechanical behaviors of granular materials from the microscopic view.This thesis investigates the effect of particle breakage and shape on the macro-and micro-mechanical behavior of granular materials based on DEM.The concrete research content is as follows:Firstly,considering that the irregular shape of particle resists particle rolling,a contact model incorporating particle rolling is implemented based on traditional DEM.The rolling resistance between the contact particles is typically used in DEM as an alternative way to consider the effect of irregular particle shape.Particle breakage is simulated by replacing crushed particles with several fragments.A particle failure criterion based on the Weibull statistical theory and a failure model in which the fragment size distribution satisfies the fractal theory are predefined.The effects of particle rolling and particle breakge on the evolution of anisotropy of granular materials are investigated using numerical biaxial compression tests.It has been observed that the rolling resistance enhances the geometrical and mechanical anisotropies,but does not appear to affect the relative weight of different anisotropies in contributing to the shear strength.Particle breakage decreases the anisotropies and also changes the relative weight of the different anisotropies in contributing to the shear strength.Secondly,irregular particles are modelling by clumped particles.For different clumped particles,the relationship of their shape feature and the rolling friction in the rolling friction model is established based on the energy dissipation of rolling.Two sets of samples,composed of clumped particles and circular particles with rolling resistance,are tested.The stress-strain relations and the evolutions of anisotropies of these samples are compared to examine the validity of employing rolling resistance to mimic the effect of particle shape.It has been found that the validity of employing rolling resistance to model the effect of shape depends on the roundness of irregular particles.This approach is less effective for irregular particles with low roundness,but more effective for irregular particles with high roundness.Finally,the 3D numerical agglomerates composed of bonded elementary balls are used to model crushable particles.The breakage behavior of granular materials under true triaxial stress conditions is investigated by DEM numerical simulation.The breakage mechanism of granular materials under different stress paths is investigated through analysing the evolution of particle size distribution and relative breakage.The quantitative comparison of the numerical results,including particle fracture strength,stress-strain relation and the relative breakage,with the experimental results verifies the correctness of numerical results.The numerical results show that the intermediate principal stress ratio has significant effects on the shear strength,dilatancy and evolution of particle breakage of crushable granular materials.The relative breakage increases with the increasing confining pressure and strain,but its increment declines gradually,which implies the existence of the optimum distribution of granular materials.The relationship between particle breakage and total input energy during tests is found to conform to a unique hyperbolic correlation.