To reveal the mechanical properties and energy laws of high-temperature rock mass engineering under fatigue disturbance, this paper conducted a multi-scale study on thermally damaged granite. First, the macroscopic mechanical properties of the samples were studied. Secondly, the law of energy evolution was summarized based on thermodynamic theory. Then, a rockburst index was introduced, and NMR and SEM technologies were used to conduct a multi-scale discussion on the mechanism of influence on temperature. Finally, an improved nonlinear continuous damage model (INCDM) was established, and a hardening index and damage growth rate of low-cycle fatigue were defined. The result shows that temperature first strengthens and then weakens the fatigue mechanical properties of the sample, with a threshold temperature of 225°C. Temperatures below the threshold cause uneven expansion of mineral particles to squeeze natural pores, reduce the porosity of the sample, and thus increase the fatigue life and strength of the sample. Temperatures above the threshold cause dehydration and phase change of the minerals such as quartz, feldspar, and mica, forming transgranular/intergranular cracks, parallel cleavage and stratification, thus reducing the fatigue strength of the sample. In addition, the total energy, elastic energy and dissipated energy density of the sample all show a step-like increasing trend with the normalized cycle index. Energy storage satisfies a linear law. Affected by accelerated energy release, energy dissipation changes from linear to nonlinear law. As the temperature increases, the rockburst tendency first increases and then decreases. The fatigue failure changes from sudden instability to progressive instability mode. The fatigue-thermal damage of the sample satisfies a power law, and increases as a compound power function with the normalized cycle index.

中文翻译：

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疲劳载荷作用下热损伤花岗岩疲劳力学性能和能量定律的多尺度研究


为揭示疲劳干扰下高温岩体工程的力学性能和能量定律，本文对热损伤花岗岩进行了多尺度研究。首先，研究了样品的宏观力学性能。其次，基于热力学理论总结了能量演化规律;然后，引入岩爆指数，并利用 NMR 和 SEM 技术对温度影响机制进行了多尺度讨论。最后，建立了改进的非线性连续损伤模型 （INCDM），并定义了低周疲劳的硬化指数和损伤增长率。结果表明，温度首先加强了样品的疲劳力学性能，然后削弱了样品的疲劳力学性能，阈值温度为 225°C。 低于阈值的温度会导致矿物颗粒不均匀膨胀，挤压天然孔隙，降低样品的孔隙率，从而增加样品的疲劳寿命和强度。高于阈值的温度会导致石英、长石和云母等矿物脱水和相变，形成跨颗粒/晶间裂纹、平行解理和分层，从而降低样品的疲劳强度。此外，样品的总能量、弹性能和耗散能量密度均随归一化循环指数呈阶梯状增加趋势。储能满足线性定律。受能量释放加速的影响，能量耗散从线性定律变为非线性定律。随着温度的升高，岩爆趋势先增大后减小。疲劳失效由突然失稳转变为进行失稳模式。 样品的疲劳-热损伤满足幂律，并随着归一化循环指数的增加而增加。