Mechanical properties of ring specimens of sandstone subjected to diametral compression

An experiment using the rings of 34 mm in thickness, 50 mm in external diameter, and 8-30 mm in internal diameter was designed via the ring test, to analyze the stress characteristics around the hole. Strain gauges were used to record the strain changing around the hole during the test, and the mechanical properties of specimens were studied. The results indicate that the peak load of the specimens decreases with the increase of internal diameter. Both the discs and ring specimens with relatively small internal diameters have abrupt failure when they reach the first peak load. However, when the diameter is greater than 16 mm, there is no clearly defined stress drop after the first peak stress, but a distinct stress drop after the second peak stress is reached. The stress at the weakest point in the ring specimen is a structural parameter rather than a material parameter, and it changes with different internal diameters. The Hobbs' equation based on elastic mechanics may not be suitable for determining the tensile strength of rock. Rock specimen needs adequate tensile deformation to fail until it reaches the limit stress. The failure of the borehole in the rock may be evaluated by the tensile deformation instead of tensile strength. The results provide important reference for mechanical characteristics of rock under compression-tension stresses.