Indentation Size Effects and the Mechanical Properties of Barite Rocks

This paper uses a combination of nanoindentation experiments and mechanism-based models to determine the dislocation densities and plasticity length scales associated with the nanoindentation of barite rock materials. These include estimates of the plasticity length scale, geometrically necessary dislocation densities (GNDs) and statistically stored dislocation densities (SSDs) that are shown to have major implications for the plastic deformation of geomaterials such as barite rocks. The statistical variations associated with the nanoindentation of barite rocks are also measured along with local variations in surface composition that are also elucidated via energy dispersive X-ray spectroscopy (EDS) during Scanning Electron Microscopy (SEM). The indentation size effects are shown to be greater than the statistical variations due to local differences in surface composition. The effects of local variations in surface composition are also discussed before relating the measured hardness values to the underlying dislocation densities (GNDs and SSDs) and plasticity length scale parameters using strain gradient plasticity theories. The presence of hard minerals such as quartz and other silicate minerals, as confirmed by the elemental composition of the rock samples, contributed significantly to the average hardness, elastic modulus, plasticity and relatively high dislocation densities. The implications of the results are discussed for the energy-efficient drilling and blasting of rocks, constitutive modeling of barite rock deformation and the crushing of rocks during mineral processing.