Study on the correlation between rock's mineral compositions and macro-micro friction properties

Mineral composition is an important factor affecting the macro-micro friction mechanical properties of rock. The macro-micro friction properties of sandstone are studied based on direct shear and nano-scratch tests，the variations of mineral compositions before and after shearing are analyzed using X-ray diffraction，the macro-micro friction coefficients of the rock，different minerals and their interfaces are statistically obtained，and the friction correlation mechanism between these factors is established. The results show that the proportion of hard-phase minerals in the total amount of powder increases after shearing，the proportion of soft-phase minerals decreases. The scratch depth and friction force of hard-phase minerals remain stable，those of soft-phase minerals vary significantly. Statistical analysis of the frequency distribution curve of the friction coefficient reveals that each mineral and interface exhibit a single-peak Gaussian distribution. Combined with the analysis of macro-micro friction mechanisms，it is found that the macro friction force of sandstone is influenced by surface asperities and the wear between different minerals，the friction force of hard-phase minerals primarily depends on their inherent properties，the friction force of soft-phase minerals and interfaces is affected by their inherent properties，plastic flow and the extrusion of surrounding minerals. By further quantifying the relationship between macro-micro friction coefficients，the hard-soft phase interface is found to contribute the most to the macro friction coefficient，accounting for 52.1%. The research results of the macro-micro friction properties can provide a theoretical foundation for revealing the mechanism of cross-scale friction mechanics.