Characterization of metakaolinite micro-mechanical behaviors using MD simulation

Abstract

The mechanical behavior of metakaolinite under nanoindentation and nanoscratching was investigated by means of molecular dynamic (MD) simulations in this study. A 6 nm radius spherical indenter was pressed on the (001) and 001¯ basal planes up to a 3.5 nm indentation depth to study the anisotropy of metakaolinite in hardness and Young’s modulus. The higher hardness was found in silica facet as it possessed a hexagonal-close-packed plane that is the most densely packed plane. During scratching, a 3 nm radius spherical indenter was used to scratch the substrate surfaces up to 8 nm length, the scratching behavior in different scratching depth and speed was studied. Both normal and scratch forces increased as the scratching processed, while scratch force showed a high dependence on scratching depth. At high scratching depth of 2.5 nm and 3.5 nm, pile-up of atoms towards the free surface and formation of chip via the shear zone were observed, the chip volume was found to increase with the increase of scratching depth. The metakaolinite appeared to soften slightly, as demonstrated by normal hardness decreased with depth. The depth dependence was more conspicuous on the scratch force than for the normal force, while the scratching speed had little effect on the scratching process.