Objective Investigating the micromechanical properties of minerals using nanoindentation tests is of great significance for revealing the microscale mechanisms behind mineral failure.
Methods Focusing on the primary minerals in the surrounding rocks of red shales in a phosphate deposit, this study conducted qualitative and semi-quantitative analyses of these minerals, including their spatial distributions, using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and targeted nanoindentation tests, determining the micromechanical properties of the minerals. This study developed a discrete numerical calculation model for the microscopic nanoindentation of minerals based on Voronoi polygons and compared the simulation results with the test results.
Results and Conclusion The results indicate that the red shales contain four minerals, i.e., quartz, albitite, chlorite, and illite, which exhibit elastic modulus of 95.62, 78.13, 53.50, and 48.91 GPa, respectively. Among them, the quartz and albitite minerals exhibit the most favorable mechanical properties, while the chlorite and illite display the worst mechanical properties, indicating that the red shales are heterogeneous and multiphase materials. Laboratory tests indicate that anomalies such as inflection points with a stepped distribution pattern in the load-displacement curves were formed by the presence of internal defects and micropores in minerals. In contrast, the simulation results show that the sharp increase in the inflection point number of the load-displacement curves was caused by the sizes, content, and spatial distributions of mineral particle clusters. The minerals differed greatly in the type, quantity, proportion, and inclination distributions of microcracks after mineral impression. This can be employed to characterize the deterioration degree and microcrack propagation direction of the minerals during loading. The results of this study assist in predicting the cracking directions of minerals under loads, provide theoretical support for the analysis of microscopic mineral degradation, and serve as a reference for the disaster prevention of surrounding rocks under similar operating conditions.
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