Multi-scale investigations on the mechanisms affecting the strength and the elastic modulus of a marble varying in texture

The study on the mechanisms affecting the strength and the elastic modulus of a crystalline rock has been focused on a marble, variable in texture, despite an almost monomineralic calcitic composition. A wide experimentation was conducted on three levels: macro-scale (scale of the laboratory sample, order of centimeters), meso-scale (several grains) and grain-scale (order of μm). The experimental results have confirmed, on the various scales, the theoretical models which assume failure occurs from pre-existing flaws, acting as stress concentrators in controlling the rock's strength. On the grain- and meso-scales, the indentations cause the brittle failure of the calcite grain along its cleavage planes and the indents are influenced by microcracks (intra-granular and inter-granular), whatever the indenter's shape (Berkovich, Vickers, Knoop). On the macro-scale, the texture markedly affects the strength, the stress-strain behavior and the failure mechanisms in Rock Impact Hardness Number (R.I.H.N.) test of the investigated rock. Furthermore, the more intense open microcracking inside the granoblastic marble causes lower values of elastic modulus, strength and P-waves velocity compared to xenoblastic marble.