基于PFC3D-GBM的晶体–单元体尺寸比对花岗岩动态拉伸特性影响分析

Study on the effect of grain size-particle size ratio on the dynamic tensile properties of granite based on PFC3D-GBM

为从矿物颗粒尺度上探究花岗岩的动态拉伸力学行为,提出一种新型的基于颗粒流方法(particle flow code,PFC)的三维等效晶质模型(grain-basedmodel,GBM),并利用FDM-DEM耦合建模技术构建三维分离式霍普金森压杆(splitHopkinsonpressurebar,SHPB)模拟系统。利用该系统对模拟岩样进行动态半圆弯拉(semi-circular bending,SCB)试验,探究试样破裂过程,并讨论晶体-单元体尺寸比对花岗岩动态拉伸力学行为的影响。研究结果表明:动载作用下的试样内部裂纹数目演化过程可分为萌生、缓慢增长、急速增长、趋于稳定4个阶段,且拉伸破坏是引起试样整体破裂的主要力学机制。随着晶体-单元体尺寸比的增加,试样晶内接触数量占总接触数量的比值逐渐上升并趋于稳定,而晶间接触占比则相应减小。试样破坏后产生的晶内裂纹数量占总裂纹数量的比值逐渐增大,导致试样发生宏观断裂时所需的外部荷载值上升,因此其动态抗拉强度上升且逐渐趋于稳定。PFC3D-GBM在研究晶质性岩石动力学方面具有可行性,是从矿物颗粒尺度上进行岩石力学探究的有力工具。

To investigate the dynamic tensile mechanical behaviors of granite at the grain scale,a novel three-dimensional grain-based model based on the three-dimensional particle flow code(PFC3 D-GBM) was proposed,and a three-dimensional split Hopkinson pressure bar(SHPB) numerical model was constructed based on the modeling technology of coupled finite difference method(FDM) and discrete element method(DEM). The numerical dynamic semi-circular bending(SCB) test was conducted on the numerical samples using the coupled SHPB system to investigate the fracturing process of the samples,and the effect of the grain size-particle size ratio on the dynamic tensile mechanical properties was also discussed. The numerical results show that,under dynamic loading,the crack number evolution process of the samples can be divided into four stages of initiation,slow development,rapid increasing and stability,and that the samples mainly show tensile failure. As the grain sizeparticle size ratio increases,the proportion of the transgranular contact to the total contact increases gradually and tends to be stable,while the proportion of the intergranular contact decreases gradually. The proportion of the transgranular cracks to the total cracks increases gradually after sample failure,increasing the external load value required for the sample brittle macroscopic fracture and hence,increasing the dynamic tensile strength.PFC3 D-GBM is feasible in the study of rock dynamics and is a powerful tool for rock mechanics investigations at the grain scale.