升温速率对高温作用后砂岩的宏细观性质影响

砂岩受到高温影响后，宏细观性质会发生不同程度的变化，400 ℃ 和1 000 ℃ 是砂岩宏细观性质变化的两个重要节点。为进一步研究升温速率对高温砂岩物理性质、力学特性以及内部微观破裂的影响，以350 ℃和 950 ℃为目标温度，开展了不同升温速率下砂岩的单轴压缩试验，单轴压缩全程采用声发射监测，采用扫描电镜分析了砂岩破坏后的细观形貌。研究结果表明：经不同升温速率处理后，350 ℃砂岩的质量、体积、密度以及纵波波速变化较小；950 ℃砂岩的质量、密度及纵波波速显著降低，体积明显增大，且升温速率越高变化率越小。350 ℃砂岩的应力?应变曲线、应力?体积应变曲线、抗压强度及弹性模量受升温速率的影响较小；950 ℃ 下砂岩试样应力?应变曲线随升温速率的增加向上偏移，抗压强度和弹性模量则先增加后达到恒定。350 ℃ 及 950 ℃砂岩的声发射振铃累计数都有随升温速率增大而减小的趋势，950 ℃ 下升温速率为1 ℃/min 时砂岩的振铃累计数最大，突发性声发射活动区域最多。对不同升温速率砂岩进行扫描电镜分析发现，升温速率对350 ℃ 砂岩的微观形貌影响较小，950 ℃ 砂岩试件则会随着升温速率的下降出现微裂纹和微孔隙数量增多、体积扩大的情况。

Effect of heating rate on macro and mesoscopic properties of sandstone after high temperature

After sandstone is subjected to high temperature, the macro and micro properties will change to different degrees. 400 ℃ and 1 000 ℃ are two important nodes in the change of the macro and meso properties of sandstone. In order to further study the influence of heating rate on the physical properties, mechanical properties and internal meso-fracture of sandstone, the uniaxial compression experiment of sandstone under different heating rates was carried out with 350 ℃ and 950 ℃. The whole process of uniaxial compression was monitored by acoustic emission, and scanning electron microscope was used to analyze the meso-morphology of destructed sandstone. After treated at different heating rates, 350 ℃ sandstone has little change in the mass, volume, density and longitudinal wave velocity, while 950 ℃ sandstone decreased significantly in the mass, density and longitudinal wave velocity, and increased remarkably in the volume, and the higher heating rate, the smaller change rate. The stress-strain curve, stress-volume strain curve, compressive strength and elastic modulus of the 350 ℃ sandstone are virtually unaffected due to the heating rate. The stress-strain curve of the sandstone sample at 950 ℃ is upwardly biased with the increase of the heating rate, the compressive strength and elastic modulus first increase and then reach a constant value; the cumulative ring-down counts of acoustic emission of sandstone at 350 ℃ and 950 ℃ have a tendency to decrease with the increase of heating rate. When the temperature is 950 ℃ and the heating rate is 1 ℃/min, the cumulative ring-down counts of sandstone and the sudden acoustic emission area are the largest; scanning electron microscopy analysis of sandstones with different heating rates showed that heating rate has little effect on the mesoscopic morphology of 350 ℃ sandstone; with the decrease of the heating rate, the number of microcracks and micropores of 950 ℃ sandstone will increase, the volume size of microcracks and micropores will also increase.