| Abstrakt: |
The ring test was proposed by Hobbs (1965) to improve the indirect tensile test (Brazilian test), consisting in performing the standard Brazilian test on a sample with an inner hole. In the present paper, it is demonstrated that the ring test is valid to estimate the tensile strength of intact rock and it can be used to generalize with an adequate interpretation of the results (using the empirical solution proposed). Until now, the ring test was not recognized as a valid laboratory test, because the available analytical solution gave incoherent results. The three important advantages of the ring test are: (i) it ensures that failure is initiated at the center. (ii) The load necessary to reach the failure of the ring is smaller as the disc failure, so it is possible to use smaller devices that are usually more accurate. (iii) In addition, with the reduction of the load, the ring test avoids plasticization close to the jaw. Furthermore, the influence of the hole eccentricity on the results was verified, but this was negligible. The sample preparation, therefore, is very simple without the need of any special devices. More than 80 indirect traction tests were performed for the present study. Finally, and very relevant, is that the empirical solution is based on tests carried out by different authors with various rock types, which follow the same trend in all cases, and is only in function of the ratio between inner and outer diameters. Highlights: The ring test improves the indirect tensile test (Brazilian test). The empirical solution is very important because until now the ring test could not be used like a regular test when the analytical solution of the ring test is not valid. The elasticity theory predicts much higher tensile strength values with the ring test than with the Brazilian test and the solution for that problem had not been found until now. The sample preparation, therefore, is very simple without the need of any special devices. [ABSTRACT FROM AUTHOR] |
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