Abstract：Theoretical analysis shows that the height-to-diameter ratio and Poisson¢s ratio are two factors influencing the stress distribution within the flattened Brazilian specimen for the test to determine the tensile strength of rock material. Through 80 3D finite element computations，the stress distributions within the specimen for various height-to-diameter ratios and Poisson¢s ratios are obtained；and it is found that a breakage cannot initiate at the center of the ending surface during the test. Breakages initiating on the compressive diameter of the ending surface of specimen are defined as valid breakages. It is found that the ratio of tensile strength to compressive strength has notable influence on Mohr maximum equivalent stress within the specimen when the test is valid. The maximum equivalent stress based on Mohr theory occurs away from the center of the ending surface of specimen for an increasing ratio of tensile to compressive strength. And there exists a perfect linear correlation between Mohr maximum equivalent stress and the ratio of tensile to compressive strength. Based on 3D finite element computational results，a method and a formula for determining the tensile strength of the flattened Brazilian specimen are presented. In this method，Poisson¢s ratio，the compressive strength and a suitable strength theory are needed to calculate the tensile strength of rock material.
