基于FDM-DEM耦合的冲击损伤大理岩静态断裂力学特征研究

Investigation on the static fracture mechanical characteristics of marble subjected to impact damage based on the FDM-DEM coupled simulation

为探究循环冲击损伤后大理岩的静态断裂力学特征,基于有限差分(finite difference method,FDM)-离散元(discrete element method,DEM)耦合的建模技术构建了三维分离式霍普金森压杆(split Hopkinson pressure bar,SHPB)数值模型,其中杆件系统和岩石试件分别采用FLAC^(3D)和PFC^(3D)程序建模。利用该模型对中心直切槽半圆盘(NSCB)试样进行了恒定子弹速度下的循环冲击,随后对受损试样进行静态三点弯曲断裂实验。通过编写Fish程序,提取试样断裂面数据,对断裂面进行重构并定量计算表面粗糙度。通过与相关室内实验结果的对比分析,验证了本文数值分析的合理性与可靠性。模拟结果表明,随着循环冲击次数的增加,试样内部微裂纹、破碎颗粒均增加。连接力场分布混乱,部分力链发生断裂。力链的变化是试样力学性能劣化的根本原因。在静态三点弯曲断裂实验中,冲击5次后试样的静态断裂韧度较天然试样产生一定程度的降低。试样在静载过程中产生的微裂纹和碎块的数量随循环冲击次数的增加而增加,断裂面粗糙度随循环冲击次数的增加而增加。

To investigate the mechanical characteristics of static fracture of marble subjected to dynamic damage after cyclic impacts,based on the modeling technology of the finite difference method(FDM)and the discrete element method(DEM)coupling,a three-dimensional numerical model of the split Hopkinson pressure bar(SHPB)was constructed,and the bar system and rock sample were modeled using FLAC^(3D) and PFC^(3D) programs,respectively.The numerical cyclic impact loading tests were carried out on notched semi-circular bend(NSCB)samples at a constant impact velocity,and then the static three-point bending fracture tests were simulated on these damaged samples.The coordinate data of the particles on fracture surfaces of the sample were extracted by compiling the Fish program,and then the fracture surface was reconstructed and the surface roughness was calculated quantitatively.The rationality and reliability of the numerical analysis were verified by comparison with the results of relevant laboratory tests.The results show that in the cyclic impact loading test,the stress-strain curve rebounds,resulting from the release of part of the stored strain energy during the unloading period.With the increase of the impact number n,the numbers of cracks and fragments generated increase.The connected force field becomes more and more chaotic and the number of broken force chains displays an increasing trend.The breakage of the force chains is the root cause of the deterioration of mechanical properties of the sample.The static fracture toughness of the sample after 5 times of impact is 53.35%lower than that of the natural sample,while the failure displacement increases.In the static loading process,more and more cracks and fragments generate as n increases.This is proof that the internal structure of the sample has been damaged in the cyclic impacts.The fracture surface roughness increases as the impact number increases.The research conclusions can provide certain guidance for the engineering practice.