Post-peak behaviour is crucial for the estimation of rock mass fracturing in cave mining operations where hard rocks can exhibit class-II or snap-back response when subjected to loading. Despite the rapid development of research into class-II rocks under compression, the corresponding behaviour in tensile tests has rarely been investigated, which is critical considering the complexity of rock mass fracturing under various stress states. The post-peak response of brittle rocks involves abrupt micro-fracturing, leading to brittle macro-scale behaviour. Controlling the fracture process using the Advanced Universal Snap-Back Indirect Tensile test (AUSBIT) allowed the acquisition of the complete macro-scale class-II behaviour in the post-peak regime, facilitating the use of advanced techniques for insights into both micro and macro-scale fracture. In this study, the AUSBIT tests with digital image correlation (DIC) and acoustic emission (AE) instrumentation were conducted to analyse the progressive failure in Calca granite and Gosford sandstone specimens. Post-test observations of the fracture surfaces were performed using a scanning electron microscope (SEM). From a macroscale viewpoint, the lateral strain control in AUSBIT enabled controlled cracking with significant lateral strain extension prior to failure accompanied by gradual energy dissipation and higher rates of AE activity as smaller magnitudes of energy are being released by each AE hit or microcrack compared to conventional Brazilian tests. The stable microcrack propagation was also identified from SEM observations with more uniform profiles of microcracks and less debris observed in AUSBIT specimens. These findings were more significant in Calca granite, which verified its extreme class-II behaviour while also demonstrating the efficiency of AUSBIT in controlling the violent failure of high-strength brittle rocks commonly encountered in deep mining projects, leading to the acquisition of more accurate material behaviour in terms of micro and macro-scale post-peak features which was unattainable from conventional indirect tensile tests.

中文翻译：

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脆性岩石的微观和宏观断裂行为：传统巴西试验与先进的通用回弹间接拉伸试验 （AUSBIT） 之间的比较


峰后行为对于估计洞穴采矿作业中的岩体压裂至关重要，其中坚硬的岩石在受到载荷时可能会表现出 II 级或回弹响应。尽管对压缩下 II 类岩石的研究发展迅速，但很少研究拉伸试验中的相应行为，考虑到各种应力状态下岩体压裂的复杂性，这一点至关重要。脆性岩石的峰后响应涉及突然的微压裂，导致脆性宏观尺度行为。使用高级通用回弹间接拉伸试验 （AUSBIT） 控制断裂过程，可以在峰后状态下获得完整的宏观尺度 II 类行为，从而促进使用先进技术来深入了解微观和宏观尺度的断裂。在本研究中，使用数字图像相关 （DIC） 和声发射 （AE） 仪器进行了 AUSBIT 测试，以分析 Calca 花岗岩和 Gosford 砂岩标本的渐进破坏。使用扫描电子显微镜 （SEM） 对断裂表面进行测试后观察。从宏观尺度的角度来看，AUSBIT 中的横向应变控制能够在失效之前实现受控开裂，并伴有显着的横向应变扩展，伴随着逐渐的能量耗散和更高的 AE 活性速率，因为与传统的巴西测试相比，每个 AE 撞击或微裂纹释放的能量大小较小。从 SEM 观察中也确定了稳定的微裂纹扩展，在 AUSBIT 样品中观察到的微裂纹轮廓更均匀，碎片更少。 这些发现在 Calca 花岗岩中更为重要，它验证了其极端的 II 类行为，同时还证明了 AUSBIT 在控制深部采矿项目中常见的高强度脆性岩石的剧烈破坏方面的效率，从而在微观和宏观尺度峰后特征方面获得更准确的材料行为，这是传统的间接拉伸测试无法实现的。