Anisotropy of mica probed by nanoindentation

Abstract

Clay minerals, abundant in soils and shales, are characterized by their distinct, nanoscale layered crystal structure that is known to result in anisotropic responses to loading. Owing to their tiny sizes, it is a significant challenge to determine their anisotropic properties. This paper presents a pioneering nanoindentation study to probe the anisotropy of a muscovite that was subjected to loading at directions both normal and parallel to the basal plane. The hardness, H, and indentation modulus, M, vary with loading directions. The load-displacement curves indicate remarkable difference during indentation loading and unloading, and the basal plane exhibits a stronger penetration resistance (i.e., H) than the edge, while the M in the direction perpendicular to the basal plane is smaller than that in the direction parallel to the basal plane. The anisotropic behavior is also interpreted along the mineral's unique layered structure as well as the nanoscale deformation mechanisms. © Springer-Verlag Berlin Heidelberg 2013.