Abstract The micro-structures of rock govern meso- and macro-scale rock behaviours and their failure mechanisms. This paper applied the experimental study (uniaxial and triaxial compressive tests) and scanning electron microscope (SEM) method to illustrate the relationship between microscopic damage and mesoscopic fracture. Specifically, this study carried out that there are three main pre-existing micro-structures including heterogeneity (31%), micro-cracks (27%), and crystal lattice boundaries (25%). The pre-existing micro-cracks are investigated and classified as inter-granular cracks (37%), intra-granular cracks (36%), and trans-granular cracks (27%) based on morphological characteristics. According to the deformation types, the micro-cracks after test are divided as tensile crack (53%), shear crack (29%), and mixed shear and tensile crack (18%). Moreover, this paper provides a damage property parameter which is the ratio of tensile damage degree to shear damage degree based on the SEM image processing technique. This parameter could reveal the damage properties (tensile or shear) at different stages including initiating stage, propagation stage and failure stage, which could present the microscopic damage development process. Finally, compared with the fractures on two specimens from compressive tests, it could confirm that the meso-scale fracturing process is associated with the micro-scale damage development process.

中文翻译：

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基于镁铁质试样的压缩试验和定量扫描电子显微镜图像处理的显微结构特性及失效过程分析

摘要 岩石的微观结构控制着中、宏观尺度的岩石行为及其破坏机制。本文应用实验研究（单轴和三轴压缩试验）和扫描电子显微镜（SEM）方法来说明微观损伤与细观断裂之间的关系。具体而言，本研究进行了三种主要的预先存在的微观结构，包括异质性（31%）、微裂纹（27%）和晶格边界（25%）。研究预先存在的微裂纹，并根据形态特征将其分为晶间裂纹（37%）、晶内裂纹（36%）和穿晶裂纹（27%）。根据变形类型，试验后的微裂纹分为拉伸裂纹（53%）、剪切裂纹（29%）、和混合剪切和拉伸裂纹 (18%)。此外，本文基于SEM图像处理技术提供了一种损伤特性参数，即拉伸损伤程度与剪切损伤程度的比值。该参数可以揭示不同阶段的损伤特性（拉伸或剪切），包括起始阶段、扩展阶段​​和破坏阶段，可以呈现微观损伤发展过程。最后，通过与压缩试验中两个试件的裂缝比较，可以证实中尺度压裂过程与微观损伤发展过程相关。该参数可以揭示不同阶段的损伤特性（拉伸或剪切），包括起始阶段、扩展阶段​​和破坏阶段，可以呈现微观损伤发展过程。最后，通过与压缩试验中两个试样的裂缝比较，可以证实中尺度压裂过程与微观损伤发展过程相关。该参数可以揭示不同阶段的损伤特性（拉伸或剪切），包括起始阶段、扩展阶段​​和破坏阶段，可以呈现微观损伤发展过程。最后，通过与压缩试验中两个试件的裂缝比较，可以证实中尺度压裂过程与微观损伤发展过程相关。