Fracturing and indirect tensile strength of brittle and ductile rocks

Abstract

Rock failure can either be referred to as brittle, ductile, or at the brittle-ductile transition. Brittle failure is said to occur when the ability of the rock resist load decreases with increasing deformation. Brittle failure is associated with the materials that undergo little to no permanent deformation before failure and, depending on the test conditions, may occur suddenly and catastrophically. Ductile failure is said to occur when the material can sustain permanent deformation without losing its ability to resist loading (without failing). Brittleness may also be defined in terms of the ratio of specific elastic strain energy at the fracture to total specific strain energy at the fracture when a fracture is accompanied by plastic deformation, it is called a ductile fracture and when plastic deformation is absent it is called a brittle fracture. There are different definitions of rock brittleness in rock mechanics literature; however, Uniaxial Compressive Strength (UCS) and BrazilianTensile Strength (BTS) values are very important parameters to determine brittleness and ductility of rocks. Thus, the study presents the obtained BTS values of rocks by using standard Brazilian Jaws. As the Brazilian test has been criticized since it was initially proposed by ISRM, the aim of this study to investigate the accuracy of Brazilian jaws to determine the BTS values of brittle and ductile rocks separately. FRANC2D software was used to analyse the stress distribution at the centre of disk specimens by considering ductility and brittleness of rocks. Both experimental and numerical results showed that both BTS values and fracturing of rocks were found depended on the brittleness and ductility of rocks and accuracy of using the proposed standard Brazilian jaws may change depending on ductility and brittleness of rocks.