The internal microstructure of rock has an important influence on its macroscopic mechanical properties and fracture mechanism. In this paper, an equivalent crystal model (ECM) consisting of a bonded particle model and smooth joint model is established, which can simultaneously reflect the structure and content of mineral granules in rock. To verify the applicability and reliability of the ECM to further study the macroscopic nonlinear mechanical behaviour and fracture mechanism of rocks from a mesoscale perspective, this paper carried out numerical simulations of direct tension, uniaxial compression and triaxial compression loading using the particle flow code software, and the numerical results were compared with the test results of Beishan granite. The main research results are summarized as follows. (1) Under the condition of triaxial compression, with the increase in the confining pressure, the axial peak strain, radial peak strain, volume peak strain and post-peak residual strain of the rock all show an increasing trend. The rock exhibits an axial splitting failure mode dominated by tensile cracks and gradually changes to a shear failure mode dominated by shear cracks at an angle of approximately 45° from the loading direction. (2) Under direct tensile conditions, the failure of the rock manifests as cracks initiating from the middle of the specimen and extending approximately perpendicular to the tensile load direction, forming an approximately horizontal macroscopic crack composed of mineral granular boundaries. (3) The use of the ECM can reproduce a high ratio of the uniaxial compressive strength to the uniaxial tensile strength of the rock, and its strength characteristics show obvious nonlinear characteristics and meet the Hoek–Brown strength criterion. The rock strength and failure type obtained from the simulation are basically consistent with the test results, demonstrating the reliability of the ECM.

岩石的内部微观结构对其宏观力学性能和断裂机理具有重要影响。建立了由结合颗粒模型和光滑节理模型组成的等效晶体模型（ECM），可以同时反映岩石中矿物颗粒的结构和含量。为了验证ECM的适用性和可靠性，从中尺度角度进一步研究岩石的宏观非线性力学行为和断裂机理，本文使用粒子流代码软件对直接拉伸，单轴压缩和三轴压缩载荷进行了数值模拟，将数值结果与北山花岗岩的试验结果进行了比较。主要研究结果总结如下。（1）在三轴压缩条件下，随着围压的增加，岩石的轴向峰值应变，径向峰值应变，体积峰值应变和峰后残余应变均呈增加趋势。岩石表现出以拉伸裂纹为主的轴向分裂破坏模式，并以与载荷方向成大约45°的角度逐渐转变为以剪切裂纹为主的剪切破坏模式。（2）在直接拉伸条件下，岩石的破坏表现为裂纹，该裂纹从试样的中部开始，并大致垂直于拉伸载荷方向延伸，形成了由矿物颗粒边界组成的近似水平的宏观裂纹。（3）使用ECM可以重现岩石的单轴抗压强度与单轴抗拉强度的高比率，并且其强度特性显示出明显的非线性特性并满足Hoek-Brown强度标准。通过模拟获得的岩石强度和破坏类型与测试结果基本一致，证明了ECM的可靠性。