Abstract
To define the critical criterion between tensile failure and shear failure of Brazilian disc is crucial for determination of tensile strength under combination of tensile and compressive stresses. A critical criterion for tensile-shear failure including tensile truncation was proposed firstly based on Mohr-Coulomb criterion. Then, a new calculation method of shear strength parameters was deduced based on the critical state stress circle. Finally, effective diameter and range of compression-tension ratio of Brazilian disc under tensile failure were proposed, and failure process of Brazilian disc from meso to macro was carried out based on numerical simulation. The results show that the modified Mohr-Coulomb criterion can be determined by two indexes of compressive strength and tensile strength. The deduced compression-tension ratio is in good agreement with experiment results. The accuracy of tensile strength test results is closely related to this ratio. When the ratio is greater than 6, failure of rock can be regarded as ideal tensile failure. If the ratio is less than 6, wedge-shape failure in loading area is the main failure type. On this condition, even if radial crack occurs, it is still not considered to be caused by pure tension.
Highlights
As quasi-brittle material, tensile strength of rock is far lower than compressive strength due to existence of micro cracks, pores and other defects
As a general method to determine tensile strength of rock-like brittle material, Brazilian disc splitting test has been written into the relevant technical specifications of China, Japan, the United States, the United Kingdom and other countries(ISRM 1978; Yangtze River Scientific Research Institute 2001)
The following are the main conclusions derived from this study: (1) From theoretical scope, compressive stress at center is exactly three times of tensile stress when the disc is split radially, which is consistent with Griffith strength criterion
Summary
As quasi-brittle material, tensile strength of rock is far lower than compressive strength due to existence of micro cracks, pores and other defects. As a general method to determine tensile strength of rock-like brittle material, Brazilian disc splitting test has been written into the relevant technical specifications of China, Japan, the United States, the United Kingdom and other countries(ISRM 1978; Yangtze River Scientific Research Institute 2001). This test method is mature and widely used, it is still a research hotspot which mainly focuses on the following aspects. Different loading methods will cause local damage to loading area, resulting in a large difference between strength of Brazilian disc and actual value For these reasons, some scholars consider that Brazilian disc splitting test cannot be used to measure tensile strength of rock material. The whole process of damage from micro damage to macro failure of the disc is analyzed and the quantitative index of Brazilian splitting tension shear conversion is put forward
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