Study On Rock Modeling Method In EDEM And Simulation On Rock Static-dynamic Characteristics

With the development of computer technology,the numerical simulation technology has become an important technical means in studying the rock fragmentation process and its regularity.Discrete element method is one of the important tools for simulating the process of rock mechanics.By establishing the correct discrete element model of the rock,which is similar in mechanical properties to the real rock,and conduct many of simulation experiments,a large amount of valuable experimental data can be obtained.The mechanical properties of the rock model are determined by the particle parameters,the bonding bond parameters,and the contact parameters.The influence of each parameter on the rock model’s mechanical properties is different,and the rock’s mechanical properties and fracture form are comprehensive manifestation of many mechanical parameters of rock.Therefore,if a kind of discrete element model which is consistent with the compressive strength,tensile strength,elastic modulus and Poisson’s ratio of real rocks,it will lay the foundation for the simulation study of complex rock mechanical processes under different kind of loads.In this paper,based on the Hertz-Mindlin with bonding（HMB）contact model in EDEM software,the relationship between the parameters of the HMB and the rock model’s mechanical properties were studied,and a method for constructing the HMB rock model was summarizes.The rock model established by this method has almost the same mechanical properties with the real rock,such as compressive strength,tensile strength,elastic modulus and Poisson’s ratio.With the HMB rock model,the static and dynamic characteristics of rock,and the relationship between crushing energy consumption and impact velocity in impact crusher were simulated.The main results are as follows:（1）According to the algorithm of the HMB contact model in the EDEM software and the different ways of tensile fracture of the bonds,the concepts of Strength Fracture Criterion（SFC）and Geometric Fracture Criterion（GFC）are suggested.The bond fractures follow the SFC is called"strong bond",and follow GFC is called"weak bond".（2）The concept of the“Fully Weak Bond HMB Rock Model”（FWBRM）is suggested,and the calculation formula of the critical contact radius coefficient for FWBRM is derived.The uniaxial compression and uniaxial tensile simulation tests with FWBRM were conducted,the relationship between the particle contact radius coefficientαand the compressive strengthσ_c,tensile strengthσ_tof the rock sample was studied.A method of construction HMB rock model which has high-pressure tensile strength ratio was established.（3）On the basis of the HMB rock model with high-pressure tensile strength ratio,the relationship of four rock mechanical parameters such as compressive and tensile strength,elastic modulus and Poisson’s ratio and the contact radius coefficient and bonding bond parameters in the HMB model were investigated.The mathematical model between the four rock mechanics parameters,the parameters of HMB rock model were established,and HMB rock model modeling steps were also summarized（4）The sandstone and granite HMB models were established and simulated.The results show that the elastic modulus,Poisson’s ratio,compressive strength and tensile strength of the HMB rock model are good agreement with the target values,and the dynamic fracture characteristics under high strain rate loads is almost consistent with the experimental results of the literature.It is proved that the HMB rock model established can be applied to both rock statics and dynamics research.（5）Analyzing the HMB contact model algorithm,bond fracture characteristics and rock crushing forms,two quantitative evaluation indexes to analyzing HMB rock model’s degree of damage and fracture were put forward.That is damage degree index and broken degree index.The damage and fracture evolution process of the rock sample during uniaxial compression simulation test was analyzed with the two indicators.The results show that the process can be divide into four stage,that are initial compaction stage,the compaction damage stage,radial expansion stage and macroscopic crushing stage.（6）The sandstone HMB model was simulated under dynamic tensile and dynamic compression loads.The result shows that both the compressive and tensile strengths of HMB specimens have strain rate correlation.When the strain rate is less than140s^-1,the dynamic compressive strength changes very small,and if strain rate is greater than140s^-1,the dynamic tensile strength increases with a power function law and the power exponent is 0.35.For dynamic tensile strength,when the strain rate is less than 40s^-1,dynamic tensile strength changes very small,and if strain rate is greater than 40s^-1,the dynamic tensile strength increases with a power function law and the power exponent is1/3.（7）A three-dimensional model of the impact crusher was established,and the impact-counterattack simulation experiment was carried out using the sandstone HMB model.The contact length between the particles in the rock HMB model before and after impacting was analyzed,and the simulation results were also quantitative analyzed.Result shows that when the rock is crushed under impact load,the fracture form mainly determined by the force transmission path.The initial damage has little effect on rock fracture.（8）According to the broken degree index,damage degree index and input power,the broken specific energy consumption and the broken damage specific energy consumption are defined,and the fracture and damage degree of the rock under the two loads of impact and counterattack were analyzed.The result shows that when the rotor speed is 600 rpm（impact velocity 25.12m/s）,the impact crusher has both higher productivity and lower specific energy consumption.