This study experimentally investigates the influence of heating/cooling cycles on the mechanical properties and cracking features of Rucheng granite. The specimens, which were previously subjected to various numbers of heating (350 °C) and cooling (in 21 °C tap water) cycles, were tested under unconfined compression. Integrated acoustic emission (AE) and digital image correlation (DIC) techniques were used to study the micro/macrocracking characteristics of the specimens upon different heating/cooling cycles. The changes in the amount of surface cracks and microcracks, P-wave velocity, unconfined compressive strength (UCS), elastic modulus, and Poisson’s ratio of the specimens prior to and after various heating/cooling cycles were comprehensively analyzed. The results showed that as the number of heating/cooling cycles increased, more surface cracks and internal microcracks (including intergranular and intragranular) were observed, leading to more remarkable decreases in P-wave velocity and substantial loss of the strength and stiffness. The change in the P-wave velocity is more sensitive than the UCS upon the cyclic heating/cooling treatments. An increase in the cycle number yielded an increase in the brittleness and a decrease in the ductility with respect to the stress-strain response. Furthermore, after exposure to a greater number of heating/cooling treatment cycles, the onset of unstable crack propagation will initiate at a lower stress threshold, while the postpeak softening response becomes more prominent. In addition, the failure mode changes from a typical shear failure to an axial splitting fashion as the number of heating/cooling cycles increases.

中文翻译：

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无限冷压缩下加热/冷却循环对汝城花岗岩微观/宏观断裂特性的影响

本研究通过实验研究了加热/冷却循环对汝城花岗岩力学性能和开裂特性的影响。在无限制压缩下测试了先前经历了各种加热（350°C）和冷却（在21°C自来水）循环的样品。集成的声发射（AE）和数字图像相关性（DIC）技术用于研究在不同加热/冷却循环下样品的微观/宏观裂纹特征。全面分析了样品在各种加热/冷却循环前后的表面裂纹和微裂纹数量，P波速度，无侧限抗压强度（UCS），弹性模量和泊松比的变化。结果表明，随着加热/冷却循环次数的增加，观察到更多的表面裂纹和内部微裂纹（包括晶间和晶内），从而导致P波速度的下降更加明显，强度和刚度大大降低。在进行循环加热/冷却处理时，P波速度的变化比UCS更为敏感。相对于应力-应变响应，循环次数的增加导致脆性增加和延展性降低。此外，在暴露于大量加热/冷却处理循环之后，不稳定裂纹扩展的开始将在较低的应力阈值处开始，而峰后的软化响应变得更加突出。另外，随着加热/冷却循环次数的增加，失效模式从典型的剪切失效变为轴向分裂形式。