Experimental analysis of the extension to shear fracture transition in a rock analogue material using digital image correlation method

This paper presents the results of axi-symmetric extension tests on a Rock Analogue Material that showed a continuous transition from extension fracture to shear fracture with an increase in compressive stress. The analysis used non destructive full-field experimental methods-digital image correlation (DIC), as well as the post-mortem specimens observation. When the mean stress was small, the fractures formed through the mode I cracking at tensile equal to the material tensile strength with smooth surfaces. These surfaces became rougher or delicate plumose patterns as the mean stress increased. Fracture angles also increased progressively from extension fractures to shear fractures. Hybrid fractures formed under mixed tensile and compressive stress states and presented plumose patterns on the rupture surface. DIC results showed the localisation of tensile deformation and the acceleration of deformation at the zone that induced the fracture. The fracture caused a reduction of deformation in the surrounding areas, which showed a release of elastic energy stored in the material during the propagation of fracture.