Mode I fracture surface of granite:: Measurements and correlations with mechanical properties

This paper deals with the experimental characterization of the fracture surface of granite, obtained from direct tensile tests. The objective is to address the dependence of Mode I fracture energy on the fracture surface's roughness, as well as to analyze the fracture propagation process based on the surface features. In addition, the influence of microstructural aspects on the fracture surface is also discussed. Different types of granites were studied, similar to the ones used in the fabric of ancient buildings, with distinct petrographical characteristics. The fracture surfaces were inspected with a novel 3D laser topographical inspection system aiming at acquiring the texture of fracture surface profiles at various locations on the surface. The relief of the fracture surfaces was characterized by means of classical parameters, namely, mean roughness and root-mean-square roughness. A deeper analysis was carried out by the separation of micro- and macroroughness regimes. This study reveals a clear linear trend between fracture energy and mean microroughness. Additionally, it was found that microstructural aspects, like planar anisotropy and grain size, as well as weathering state, influence the fracture surface. The results allow further understanding of the fracture process in quasi-brittle materials and contribute to the assessment of the mechanical characterization of granite under tension.