The direct and Brazilian tension tests are the most popular methods for measuring the tensile strength of rocks. While the values of tensile strength obtained from these test are theoretically expected to be identical, the accumulated experimental data show that the direct tensile strength is different from the Brazilian tensile strength in most cases. In an attempt to explore the potential reasons for such discrepancy, the direct and Brazilian tension tests are compared in the light of size effect and bimodularity. The problem of size effect is investigated using the two approaches of statistical theory of strength and linear elastic fracture mechanics. The effect of bimodularity of the material on the induced stresses in the tension tests is also examined. Based on the effect of size and bimodularity, equations have been derived to relate the direct and Brazilian tensile strength. The results of the direct, Brazilian and fracture toughness tests on Lac de Bonnet granite were used to validate the equations.
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机译：直接和巴西张力试验是测量岩石拉伸强度最流行的方法。虽然从这些测试获得的拉伸强度的值在理论上是相同的，但累积的实验数据表明，在大多数情况下，直接拉伸强度与巴西拉伸强度不同。为了探索这种差异的潜在原因，将直接和巴西张力试验在尺寸效应和双倍性的光线中进行比较。研究了尺寸效应的问题，采用了强度和线性弹性裂缝力学统计理论的两种方法研究。还检查了材料对张力试验中诱导应力的影响。基于尺寸和双倍性的效果，推导出方程以涉及直接和巴西拉伸强度。 Lac de Bonnet花岗岩的直接，巴西和断裂韧性试验的结果用于验证方程。
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