Shear stress triggering brittle shear fracturing of rock-like materials

Contact fracturing of rock-like brittle materials indented by rigid cylindrical punches with flat ends is studied. Contrary to the classical shear fracturing mechanism of brittle materials explained in terms of multi-tensile-stressed micro-cracks in materials [1], a new mechanism dominant in brittle shear fracturing is found, namely, shear stress triggered fracturing orientation existing in nature, and the contact crack initiation angle for such kind rock-like materials is also revealed. This phenomenon is very different from such as Hertzian or Roesler's [2] crack generation mechanism, as cracks are directed inwards rather than outwards. The theoretical predictions are validated by our experimental results. This finding testifies that for a rock-like brittle material shear fracturing along its maximum shear stress plane is possible under some special confinement, which has important implications for seismology and rock-mass stability, as well as rock engineering.