Numerical Investigation Of Particle Crushing Behavior Bv Discrete Element Method

Granular materials are commonly encountered in nature and a variety of industrial processes.Granular particles will break when the external load acting on it is larger than its critical value.The fragmentation of particles will obviously influence the pressure drop across the whole assembly and also the thermal-mechanical properties of the system.Thus,accurately predicting the breakage of particles is obviously useful to the better controlment and optimization of any equipment related to the handling of granular material.Experimentally,the failure strength of granular particle is usually obtained through performing uniaxial compressive test.Nevertheless,inside real granular assembly,a given particle might interact with several neighbor particles at the same time,and the spatial arrangement of contacting neighbor particles varies from particle to particle.It thus raises an important question:can the results obtained from uniaxial compressive test be used to other loading condition,i.e.,is there a unique particle breakage criterion that can be applied to any loading condition?Targeting at this question,in this work the breaking behavior of granular particle is investigated by performing three-dimensional Discrete Element Method(DEM)simulations.In chapter two,the DEM contact model used in this work is introduced.And the possible influences of loading rate and also the size of sample on the predicted variation of stress are discussed.Based on the simulation results,proper loading rate and sample size is then identified.In chapter three,the possible influences of bond property setting are investigated by modeling the mechanical responses of rectangular samples under tensile and compressive loadings.It is found that,for given brittle material,there only exist one tensile/shear bond strength setting that can ensure both the predicted tensile strength and compressive strength are in quantitatively agreement with experimental data.The simulation results indicate that the failure of samples under tensile loading is dictated by the nucleation of crack,whereas for compressive loading it is linked to the coalescence of cracks.By monitoring the time sequence of bond breakage and its failure mode,it is found that for tensile loading the dominate failure mode of bond is tensile fracture,whereas for compressive loading it is shear fracture.For the conditions considered in this work,the simulation results show that the influence of the distribution of bond strength on the compressive fracture strength of sample is minor,whereas for tensile fracture strength,it depends on the type of distribution.In chapter four,the crushing behavior of spherical aggregating under different loading configurations is investigated by performing both particle loading tests and wall loading tests.The simulation results are then used to evaluate the applicability of five particle breakage criteria reported in literature:major principal stress criterion,maximum tensile stress criterion,mean principal stress criterion,the octahedral shear stress criterion and maximum contact force criterion.The simulation results indicate that only the maximum contact force at crushing keeps nearly constant with the number variation of loading contact.Nevertheless,for given loading contact number,the obtained maximum contact forces at crushing show clear dispersion.The uniaxial,biaxial and triaxial wall loading tests demonstrate that the dispersion of the maximum contact force is minor for given loading configuration,and the maximum contact force does vary with loading contact number.All these simulation results suggest that,when using the above mentioned criteria to evaluate the breakage of particle,the influences of the number and also the spatial arrangement of loading contacts should be taken into account.In chapter five,a brief summary of this work is presented and the possible future works are addressed.