Tensile strength is one of the important mechanical properties of rock and rock-like materials and its accurate estimation and understanding of its failure mechanism are crucial for efficient design of structures on or within the rock masses. Amongst various approaches developed for estimating this property, Brazilian testing has received considerable attention analytically, numerically and experimentally. The test has been deployed for a wide range of materials such as rock, concrete, and ceramic, however its fracturing process at micro and macro scales has not yet been properly characterized. Thus, in this study, for a full understanding of the fracturing process of different rock types under indirect tensile loading, the coupled Acoustic Emission (AE) and high-speed imaging techniques were used to characterize the generated micro and macrocracks under Brazilian loading. The characteristics of AE parameters and the evolution of micro-macro cracks were investigated for three different rocks including sandstone, coal and granite at different sizes and loading configurations. A systematic framework was developed to exhibit the link between micro and macro fracturing processes under Brazilian loading. It was noted that the tensile microcracks are the first to initiate during the Brazilian failure with high intensity compared to shear microcracks. Transition in microcracking mechanism from tension to shear was evident in the samples with high brittleness. The tensile microcracks showed ascending trends with a decrease in geometrical or volumetric sample size for granite and sandstone, while its trend for coal was inconclusive due to its unique intrinsic fracture network or so-called “cleat network”. At macro scale level, single and multiple cracking mechanisms were observed in the tested samples where those with high shear microcracks mostly revealed failure under multiple cracking. Finally, some insights were provided into the transition from single tensile cracking to multiple tensile/shear cracking based on high-speed image data with high resolution.

抗拉强度是岩石和类岩石材料的重要力学特性之一，其准确估计和对其破坏机制的理解对于岩体上或岩体内结构的有效设计至关重要。在为评估该属性而开发的各种方法中，巴西测试在分析、数值和实验方面受到了相当大的关注。该测试已用于多种材料，如岩石、混凝土和陶瓷，但其微观和宏观尺度的压裂过程尚未得到适当表征。因此，在本研究中，为了全面了解不同岩石类型在间接拉伸载荷作用下的破裂过程，耦合声发射 (AE) 和高速成像技术用于表征在巴西载荷下产生的微裂纹和宏观裂纹。研究了砂岩、煤和花岗岩三种不同岩石在不同尺寸和加载配置下的声发射参数特征和微观-宏观裂纹的演化。开发了一个系统框架来展示巴西加载下微观和宏观压裂过程之间的联系。值得注意的是，与剪切微裂纹相比，拉伸微裂纹是巴西破坏过程中最先出现的高强度微裂纹。在高脆性样品中，微裂纹机制从拉伸到剪切的转变很明显。花岗岩和砂岩的拉伸微裂纹呈上升趋势，几何或体积样本尺寸减小，而煤由于其独特的固有裂缝网络或所谓的“割理网络”，其趋势尚无定论。在宏观尺度上，在测试样品中观察到单一和多重开裂机制，其中具有高剪切微裂纹的样品大多在多重开裂下失效。最后，基于高分辨率的高速图像数据，对从单一拉伸裂纹到多重拉伸/剪切裂纹的转变提供了一些见解。在测试样品中观察到单一和多重开裂机制，其中具有高剪切微裂纹的样品大多在多重开裂下失效。最后，基于高分辨率的高速图像数据，对从单一拉伸裂纹到多重拉伸/剪切裂纹的转变提供了一些见解。在测试样品中观察到单一和多重开裂机制，其中具有高剪切微裂纹的样品大多在多重开裂下失效。最后，基于高分辨率的高速图像数据，对从单一拉伸裂纹到多重拉伸/剪切裂纹的转变提供了一些见解。