Abstract
The failure of rock materials in the form of rings subjected to line loadings on either their internal or external surfaces is studied. Formulae for the stresses and some numerical values are given. Experimental results for three fine-grained rocks are given and values of the tensile strengths so obtained are compared with those from direct tension, indirect tension (Brazilian) and bending tests. It is found that the calculated tensile stresses at failure for rings loaded in either fashion, and for bending tests, are considerably higher than those for direct tension or the indirect tensile (Brazilian) test. It is suggested that this is due to the fact that in the two latter cases the stresses are uniform (or nearly so) over the section in which failure takes place, while in the three former they vary almost linearly across it. This suggests that a criterion for failure must not simply involve the stresses at a point, but also their rate of change with position.