Micromechanical properties and homogenization of sandstone based on nanoindentation

The composition and micromechanical properties of rock minerals have important effects on its macroscopic mechanical performance. The composition, proportions, and morphology of sandstone minerals are determined using an energy dispersive spectrometer and optical microscopy. The elastic modulus and hardness of each mineral component are then measured through nanoindentation tests. The equivalent elastic modulus and Poisson's ratio of sandstone are obtained using the dilute and Mori–Tanaka homogenization schemes and compared with the elastic modulus and Poisson's ratio measured in uniaxial compression tests. Finally, the influence of various microscopic parameters on the macroscopic mechanical properties of sandstone is analyzed. The results indicate that sandstone is mainly composed of quartz, feldspar, biotite, and chlorite, which can be distinguished and recognized by color and morphological characteristics under an optical microscope. Quartz has a dense structure and good mechanical properties, while biotite and chlorite have obvious pore structures and the worst mechanical properties. The equivalent Poisson's ratio obtained by homogenization is basically consistent with the macroscopic Poisson's ratio measured through testing, but the equivalent elastic modulus is greater than the test results. The Mori–Tanaka scheme gives the largest deviation in the equivalent elastic modulus. Parameter analysis shows a positive correlation between the microscopic and macroscopic mechanical properties of each mineral component. The volume fractions of quartz and feldspar are positively correlated with the macroscopic mechanical properties, while chlorite exhibits a negative correlation. The macroscopic mechanical properties of sandstone are most sensitive to changes in the mechanical properties and volume fraction of chlorite.