New brittleness indices to describe rock failure under compressive load

Brittleness is an important mechanical property of rock. There are several brittleness criteria exist to characterize rock failure based on rock mechanical properties. However, there is not a unique criterion available able to describe quantitative rock brittleness. In this study different rocks with uniaxial compressive strength values ranging between 7-215 MPa were tested to measure pre-peak and post-peak stress-strain relations. A stiff servo-controlled machine was used to undertake lateral displacement controlled tests. Post-peak stress-strain relations were obtained accurately using three-dimensional digital image correlation technique. Several brittleness indices were proposed based on pre-peak energy, elastic energy and post-peak energy. Analysing of the results demonstrated that a pre-peak stress-strain brittleness index proposed solely based on pre-peak stress-strain behaviour doesn't show any correlation with rock peak strength. On the other hand, the proposed brittleness indices based on pre-peak and post-peak stress-strain relations were found to competently describe an unambiguous brittleness scale against rock strength.