Rocks in nature contain a large number of defects and exhibit strong heterogeneity on grain scale. In this study, a novel three-dimensional multiscale method is proposed to investigate the dynamic behaviors and microfracturing in granitic rocks. In this numerical method, the heterogeneity in mineral components is reproduced by a series of a space filling Voronoi tessellations and particle filling in subgrains as computational nodal points to allow for transgranular fracturing. The rupture strength, temporal deformation fields, and failure patterns are compared with the experimental results to verify the reasonability and accuracy of the proposed method. Then, the underlying mechanism of grain-scale fracturing leading to fractal fracture surfaces, pervasively grain pulverization and deflection/penetration cracking model are discussed. It's shown that the fracture surface roughness is fractal dominated by two competitive mechanisms. The crack initiation time of intergranular tensile crack, transgranular tensile crack and shear cracks is gradually increased. The ratio of the number of tensile cracks exceeds 90% and that value of intergranular crack decreases from 56% to 33% as the strain rate increases. The appearance of multicracks activation and the transition from intergranular fracturing to transgranular fracturing is the underlying mechanism of rate dependency for granitic rocks.

自然界中的岩石含有大量缺陷，并且在粒度上表现出很强的异质性。在这项研究中，提出了一种新颖的三维多尺度方法来研究花岗岩岩石的动力学行为和微裂缝。在这种数值方法中，矿物成分的异质性通过一系列空间填充的Voronoi镶嵌和子颗粒中的颗粒填充（作为计算结点）来再现，以实现粒状压裂。将断裂强度，时间形变场和破坏模式与实验结果进行比较，以验证该方法的合理性和准确性。然后，讨论了导致分形断裂表面的晶粒大尺度断裂的潜在机理，普遍的晶粒细化和偏斜/穿透裂纹模型。它' s表明，断裂表面粗糙度是分形的，受两个竞争机制的支配。晶间拉伸裂纹，晶间拉伸裂纹和剪切裂纹的裂纹萌生时间逐渐增加。随着应变率的增加，拉伸裂纹的数量比例超过90％，晶间裂纹的值从56％降低至33％。多裂纹活化的出现以及从晶间压裂到跨晶压裂的转变是花岗岩岩石速率依赖性的潜在机理。随着应变率的增加，拉伸裂纹的数量比例超过90％，晶间裂纹的值从56％降低至33％。多裂纹活化的出现以及从晶间压裂到跨晶压裂的转变是花岗岩岩石速率依赖性的潜在机理。随着应变率的增加，拉伸裂纹的数量比例超过90％，晶间裂纹的值从56％降低至33％。多裂纹活化的出现以及从晶间压裂到跨晶压裂的转变是花岗岩岩石速率依赖性的潜在机理。