Timely spread characteristics of micro- and meso-scale fractures based on SEM experiment

Abstract

Macroscale fracture of rocks is a progressive process consisting of the initiation, propagation and coalescence of numerous microcracks, but the micro- and meso-crack propagation process and the accuracy parameters of multiscale crack evolution timely have not been studied systematically. This study investigates the micro- and meso-damage evolution characteristics based on in-situ scanning electron microscopy (SEM) tests of marble specimens under compression. The propagation and evolution characteristics of microcracks at different locations in marble specimen under load are analyzed in detail. The qualitative analysis of micro- and meso-crack propagation of marble specimen under different loading is performed. The results show that during the compression process of marble from a microscopic point of view, there are mainly three types of microcracks between mineral crystals and mineral crystals: through-grain cracks, transgranular cracks and intragranular cracks. The microcracks that dominate the failure of marble samples are intergranular cracks, and intragranular cracks do not play a significant role. The initiation and evolution of micro-fractures are carried out in zones. Unlike the macro-scale, which is basically a single-wing crack initiation, multiple micro-wing cracks initiate from the end of a prefabricated crack, and some micro-cracks close successively during the loading process, the main wing cracks also undergo a slow or even non-propagating stage. Distribution rules of different micro-parameters are obtained, the transformation from micro-scale to meso-scale is realized. Besides the study provides parameters for the study of a multi-scale theoretical model of rock deformation and failure. Different samples have different characteristics of damage expansion, and the warning before instability is different. This study will provide a warning for possible larger fractures in engineering under different conditions.