Dynamic Failure Simulations Of Brittle Material Based On Discrete Element Method

The mechanical behavior of quartz glass material under dynamic load is simulated by using discrete element method(DEM).Based on the flat-jointed bond model of two dimensional,the microscopic mechanical parameters of the quartz glass model were determined by comparing the standard uniaxial compressive/tensile and three-point bending numerical test results with the experimental results.Using these material parameters:1.The numerical simulation reproduces the process of fragmentation during impact compression of quartz glass block under SHPB,validating the strain rate effect of quartz glass,and analyzes the different failure modes of quartz glass under different strain rates.2.The numerical simulation reproduces the experiment on the edge impact of the quartz glass plate.Meanwhile,the propagation of the cracks is analyzed and compared with the existing experiments and the simulation qualitatively.3.The numerical simulation reproduces the experiment on the Taylor impact of the quartz glass rod,analyzing the process of crack propagation and the special damage structure formed by the glass rod,further research shows that:(1)The proportion of the compression failure area increases with the increase of the impact velocity,and the proportion of the tensile spall area decreases with the increase of the impact velocity;(2)The wave velocities of Destructive waves and elastic waves are basically the same,and do not change with the change of the impact velocity.But the smaller the impact velocity is,the smaller the crack in the compression failure zone(Mainly manifested in less shear cracks),the more difficult it is to form the failure surface;(3)The propagation velocities of the destructive wave front are the same in different regions on the glass bar under the equal impact velocities,it will not decrease with the increase of the propagation distance;(4)the propagation of the destructive wave front is not a process from fast to slow,but from denseness to sparsity.4.The numerical simulation reproduces the experiment on the oblique impact of the quartz glass rod,analyzing the process of crack propagation and the damage structure formed by the glass rod,It is found that the number of cracks in the compression failure zone and the spallation zone decreases with the increase of the inclination angle.Then,the three-dimensional flat-jointed bond model is calibrated,the numerical simulation reproduces the experiment on the expansion of the quartz glass ring.The fragmentation processes of quartz glass rings under different impact velocities were numerically simulated.The numerical results showed that: the failure time of the quartz glass ring corresponded to a rebounding of the radial velocity,macroscopically this timing is coincident with the rapid drop of average stress.This radial velocity rebounding is attributed to the unloading waves incited from the brittle cracking of the tensile specimen,and can be used in the numerical analysis as the failure point.Detailed numerical tests and analysis showed that:(1)The fracture strain of quartz glass ring increases with the increase of strain rate,a phenomenon consistent with experimental observations for ductile materials;(2)The average mass of the quartz glass ring decreases with the increasing strain rate;(3)The average fragment size in the simulation was consistent with the theoretical and experimental data in other papers.An experiment device of liquid-driven expanding ring was used to conduct preliminary tests.The morphology and the number of fragments recovered from real tests are consistent with the numerical simulations.