The effect of high temperatures up to 800 °C on the physical and mechanical characteristics and fracturing behaviour of Beishan granite is experimentally studied with a combination of acoustic emission (AE), digital image correlation (DIC) and optical microscope observations. The experimental results show that the responses of the P-wave velocity, the effective porosity, Young’s modulus, and the uniaxial compressive strength (UCS) of the granite to temperature are different. The critical temperature for the brittle–ductile transition of Beishan granite is between 500 and 600 °C. The counts, cumulative energy, b value, and waveform from AE and the full-field deformation evolution from DIC are combined to investigate the damage evolution and fracture mechanism in heated granite. It is found that a rise in temperature increases the number of AE events but reduces the cumulative energy release. Tensile microcracking mainly occurs in granite exposed to low temperatures, while shear fracturing gradually dominates in granite exposed to higher temperatures. With increasing temperature from 25 to 800 °C, the failure mode of granite specimens changes from being controlled by longitudinal splitting cracks to a single shear fracture and finally to multiple conjugate shear fractures. Microscopic observation of granite thin sections is conducted to further reveal the essential mechanism driving the physical–mechanical response and fracturing behaviour of heated Beishan granite.

中文翻译：

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DIC和AE技术高温处理北山花岗岩损伤断裂特性试验研究

结合声发射 (AE)、数字图像相关 (DIC) 和光学显微镜观察，实验研究了高达 800 °C 的高温对北山花岗岩物理机械特性和断裂行为的影响。实验结果表明，花岗岩的纵波速度、有效孔隙率、杨氏模量和单轴抗压强度（UCS）对温度的响应是不同的。北山花岗岩脆韧转变临界温度在500～600℃之间。AE 的计数、累积能量、b 值和波形以及 DIC 的全场变形演化相结合，研究加热花岗岩的损伤演化和断裂机制。发现温度升高会增加 AE 事件的数量，但会减少累积能量释放。拉伸微裂主要发生在暴露于低温的花岗岩中，而剪切破裂在暴露于较高温度的花岗岩中逐渐占主导地位。随着温度从25°C升高到800°C，花岗岩试件的破坏模式由受纵向劈裂控制的破坏模式转变为单次剪切断裂，最终转变为多次共轭剪切断裂。对花岗岩薄片进行显微观察，以进一步揭示驱动受热北山花岗岩物理力学响应和破裂行为的基本机制。而剪切压裂在暴露于较高温度的花岗岩中逐渐占主导地位。随着温度从25°C升高到800°C，花岗岩试件的破坏模式由受纵向劈裂控制的破坏模式转变为单次剪切断裂，最终转变为多次共轭剪切断裂。对花岗岩薄片进行显微观察，进一步揭示了驱动受热北山花岗岩物理力学响应和破裂行为的基本机制。而剪切压裂在暴露于较高温度的花岗岩中逐渐占主导地位。随着温度从25°C升高到800°C，花岗岩试件的破坏模式由受纵向劈裂控制的破坏模式转变为单次剪切断裂，最终转变为多次共轭剪切断裂。对花岗岩薄片进行显微观察，进一步揭示了驱动受热北山花岗岩物理力学响应和破裂行为的基本机制。