The Brazilian test has been extremely popular while prompting significant debate. The main source of controversy is rooted in its indirect nature; the material tensile strength is inferred upon assuming that cracking initiates at the centre of the sample. Here, we use the Griffith criterion and finite element analysis to map the conditions (jaws geometry and material properties) that result in the nucleation of a centre crack. Unlike previous studies, we do not restrict ourselves to evaluating the stress state at the disk centre; the failure envelope of the generalised Griffith criterion is used to establish the crack nucleation location. We find that the range of conditions where the Brazilian test is valid is much narrower than previously assumed, with current practices and standards being inappropriate for a wide range of rock-like materials. The results obtained are used to develop a protocol that experimentalists can follow to obtain a valid estimate of the material tensile strength. This is showcased with specific case studies and examples of valid and invalid tests from the literature. Furthermore, the uptake of this protocol is facilitated by providing a MATLAB App that determines the validity of the experiment for arbitrary test conditions.
翻译:巴西的测试非常受欢迎,同时引发了激烈的辩论。主要争议的根源在于其间接性质;物质抗拉强度的推论依据是假设裂缝在取样中心开始发生。这里,我们使用 Griffith 标准和有限元素分析来绘制导致中心裂缝分离的条件(jaws 几何和物质特性)的地图。与以往的研究不同,我们并不局限于评价磁盘中心的压力状态;通用的 Griffith 标准的失败封套用于确定裂缝点。我们发现,巴西试验有效的条件范围比先前假设的要窄得多,而目前的做法和标准对大量类似岩石的材料来说是不合适的。获得的结果被用来制定实验家能够遵循的规程,以获得对材料裂缝的有效估计。与以往的研究不同,我们并不局限于评估磁盘中心的压力状态;一般的 Griffith 标准的失败封套用于确定裂缝位置。此外,我们通过提供MATLAB App,确定任意试验条件的有效性,从而便利了这项协议的接受。