Some Features of Cleavage Cracks in Rocks and Metals

Abstract

The cracking of some rocks, namely granite, serpentinite and sandstone under tensile stress is examined in details. Brazilian testing or diametral compression, three points bending and explosion testing are used as the loading schemes in air at room temperature. Morphology of cracks in the model rocks are compared with cracks in silicon crystals, as the standard of a brittle crack, with cleavage cracks in iridium single crystals and with cracks in gallium-covered aluminum single crystals. The comparison of cracks between themselves has shown that there is additional channel for stress accommodation in the model rocks. This channel does not lead to transformation of a rock into a macroscopically ductile material, but it causes the arrest of the dangerous crack in it under tensile stress. Its influence causes transition from the brittle crack to the pore-like crack on the microscopic scale. The most probable mechanism of this transition is the dislocation emission from crack, which becomes possible in such a natural covalent solid as a rock due to Rehbinder's effect.