北山花岗岩细观非均质性对单轴压缩力学特性影响的FDEM数值研究

Study on mechanical properties of Beishan granite meso-heterogeneity under uniaxial compression with FDEM

为了研究细观非均质性对北山花岗岩中微裂纹萌生、扩展和贯通等破裂过程的影响,基于有限元/离散元耦合方法(FDEM)和数字图像处理技术(DIP),结合矿物晶体模型(GBM),分别构建3类北山花岗岩细观结构表征模型:聚类均布模型、Voronoi颗粒模型和聚类镶嵌模型。基于3类模型开展了单轴压缩试验研究,探究细观非均质性对北山花岗岩力学特性、声发射(AE)特征以及颗粒尺度裂纹扩展规律的影响。研究结果表明:3类模型均能捕获从微破裂损伤至宏观破裂的演化过程,即首先以晶间张拉裂纹为主,随后产生穿晶断裂,转变为以晶内裂纹为主,张拉破坏占主导地位;细观结构表征方式对模拟岩石的特征应力(启裂应力和损伤应力)控制效应非常显著;Voronoi颗粒模型和聚类镶嵌模型的AE特征与室内试验更为吻合;硬矿物含量的增大,会导致单轴抗压强度、特征应力和弹性模量增大,而泊松比反之;颗粒尺寸的增大,会导致单轴抗压强度和损伤应力明显减小;特征应力与刚度非均质性因子呈负相关。

In order to study the influence of the meso-heterogeneity on the initiation,propagation and coalescence of microcracks in Beishan granite,three types of meso-structure characterization models(cluster uniform model,Voronoi grain model and cluster tessellation model)were constructed based the combined finite-discrete element method(FDEM)、digital image processing(DIP)and grain based model(GBM).Based on the three types of models,uniaxial compression tests were carried out to study the influence of heterogeneity on the mechanics characteristics,acoustic emission(AE)characteristics and grain-scale crack propagation law.The research results show that three types of models can capture the evolution from micro-damage to macro-failure,intergranular tension cracks were firstly generated,then intragranular cracks were generated,and the cracks were mainly tensile cracks.The meso-structure characterizations effect significantly crack initiation stress(CI)and crack damage stress(CD).The AE characteristics of Voronoi grain model and cluster tessellation model were more consistent with the laboratory tests than cluster uniform model.With the increase of hard mineral content,the uniaxial compressive strength(UCS),elastic modulus,CI and CD increased,but Poisson’s ratio decreased.With the increase of grain size,UCS and CD decreased.With the increase of stiffness heterogeneity factor,UCS,CI and CD decreased.