Electron scanning characteristics of rock materials under different loading methods: a review

To reveal the connection between the microscopic morphological characteristics of rock fractures, crack nucleation, extension, fracture modes, and rock damage processes, this paper systematically reviews the scanning electron microscopic (SEM) morphological characteristics of rock specimens using seven different testing methods. The characteristics of the microscopic fracture morphology of specimens under triaxial extension were experimentally investigated and the relevant factors affecting the microscopic morphology of rock materials were summarized. It was found that the fracture surfaces of rocks fracturable at a low energy are usually intergranular, and those of rocks fracturable at high energy are usually trans-intergranular; the transition from intergranular fractures to trans-intergranular fractures can be observed due to the increase of confining pressures during triaxial extension. In addition, except for the structure of the rock specimen itself, external conditions such as temperature can also affect the microscopic fracture characteristics of the rock to varying degrees. In addition, the analysis of specific microstructural compositions and grain fracture surface patterns will be more effective in providing an understand the microfracture mechanics mechanisms of the specimens. The results of this study will help establish a bridge between microscopic damage mechanisms and macroscopic fracture analyses. Article highlights The microscopic characteristics of rock specimens under different loading methods were reviewed The cross-sectional microscopic characteristics of three typical rocks after triaxial extension were analyzed The factors affecting the microfracture characteristics of rocks are discussed