Understanding the fracture behavior of rock after thermal treatment is important in the deep rock engineering, such as nuclear waste disposal and geothermal energy exploration. In this work, to investigate fracture properties of thermally treated rock under compression-shear loading, a series of variable angle shear (VAS) tests were performed on shear-box (SB) granite specimens exposed to temperatures from 25 °C to 600 °C. The results indicate that the mode II fracture toughness KIIC and shear modulus G of granite increase with temperature up to 300 °C, and then decrease. The deformation evolution of specimens was analyzed using a two-dimensional digital image correlation (2D-DIC) technique. It is found that wing cracks at all temperature firstly initiate from the upper notch tip prior to 40 % of peak load. The fracture mechanism of wing crack is identified as mixed mode I-II fracture via a displacement analysis, while dominant mechanism varies at different positions along wing crack paths. The influence of wing crack on overall fracture behavior was explored in detail and the load condition for wing crack initiation was verified based on the general maximum tangential stress (GMTS) criterion. In addition, the influence of temperature on the roughness of mode II fracture surfaces was investigated based on 3D optical scanner and fractal theory. The results show that the roughness of fracture surfaces firstly decreases from 25 °C to 300 °C then increases with temperature. There is a negative correlation between the KIIC and the roughness of fracture surfaces. Finally, a more rigorous strategy is proposed to assess the reliability of new methods for estimating KIIC.

中文翻译：

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热处理花岗岩在压剪载荷下的断裂行为


了解热处理后岩石的断裂行为在深部岩石工程中非常重要，例如核废料处理和地热能勘探。在这项工作中，为了研究热处理岩石在压缩剪切载荷下的断裂特性，对暴露于 25 °C 至 600 °C 温度下的剪切箱 （SB） 花岗岩试样进行了一系列可变角度剪切 （VAS） 测试。 结果表明：花岗岩的II型断裂韧性KIIC和剪切模量G随温度升高至300 °C后降低;使用二维数字图像相关 （2D-DIC） 技术分析标本的变形演变。研究发现，在所有温度下，机翼裂纹首先在峰值载荷的 40% 之前从上缺口尖端开始。通过位移分析，将机翼裂纹的断裂机制确定为混合模式 I-II 断裂，而主要机制在沿机翼裂纹路径的不同位置变化。详细探讨了机翼裂纹对整体断裂行为的影响，并根据一般最大切向应力 （GMTS） 准则验证了机翼裂纹萌生的载荷条件。此外，基于三维光学扫描仪和分形理论研究了温度对模式 II 断裂表面粗糙度的影响。结果表明：断裂表面的粗糙度从 25 °C 到 300 °C 先降低，然后随温度升高;KIIC 与裂缝表面的粗糙度呈负相关。最后，提出了一种更严格的策略来评估估计 KIIC 的新方法的可靠性。