Abstract:
In this study three series of indirect tensile tests, the Brazilian test, the flattened Brazilian (FB) test and the ring test, were performed in order to determine the indirect maximum tensile stress of Dionysos marble. A number of circular disc specimens (D = 54 mm) was prepared by coring Dionysos marble cubes normal to the plane of transverse isotropy. Different sets of circular discs were prepared by varying the loading angle 2a and the internal diameter for the FB test and ring test respectively. All specimens were prepared by following the ISRM suggested methods and the load was applied using a stiff 1600 kN MTS hydraulic testing machine and a 500 kN load cell. This paper focuses on the comparison of the indirect maximum tensile stress resulting from the three different tests and the calculation of the theoretical and experimental coefficient k for the FB test and ring test. The coefficient k is a function of the loading angle 2a and the ratio q (internal to external diameter) for the FB test and the ring test respectively.
Introduction
It is well known that tensile failure is an important phenomenon in the mechanical winning of minerals, drilling and blasting of rocks, rock failure of underground and surface works, as well as in structural engineering practice. Therefore, the reliable experimental determination of the tensile strength of rocks is essential to the design of such systems.
Conventionally, the tensile strength of rock should be determined using the direct tension test; however, this test presents experimental difficulties and is not commonly conducted in rock mechanics laboratories. These difficulties arise due to both the bending stresses or torsion moment (caused by the eccentricity of machine axial loads) and the localized concentrated stresses (caused by improper gripping of specimens) (Barla and Goffi, 1974, Nova and Zaninetti, 1990).
