低温条件下红砂岩动态力学性能试验研究

Experimental study on dynamic mechanical properties of red sandstone under low temperatures

应用SHPB试验和分形方法研究饱水冻结红砂岩的动态力学性能和破碎分形特性,分析负温变化对红砂岩动态强度性能和变形破坏规律的影响,结合SEM扫描实验,探究应力波作用下饱水冻结红砂岩的微观破裂机制。研究结果表明,负温变化显著影响红砂岩的动态力学性能和分形特性,其中动态强度随温度降低(25^-40℃)呈先增大后减小的趋势,形似"几"字形,峰值应变则是先减小后增大,这与冻岩的静载试验结果迥然不同。经引入分形维数D,建立冻结红砂岩块度分形计算模型,经模型计算得到红砂岩在25,-5,-10,-20,-30,-40℃时的分形维数分别是2.37,2.12,2.29,2.35,2.41,2.44,这与试验筛分结果基本吻合。通过对红砂岩断口形貌的观察和分析,发现低温条件下红砂岩最终断口多发生于黏土胶结物上或其与矿物颗粒的交界处,常温条件下红砂岩断口形貌较为复杂,很难看出规律性,但在引入低温梯度后,由黏土胶结物和矿物颗粒组成的断口形貌会逐渐呈现出规律性,在对相应规律分析总结后推断,负温条件下胶结物的性质和断裂性能对红砂岩力学性能有着更为显著的影响。

The dynamic mechanical properties and fracture fractal characteristics of saturated red sandstone under low temperatures are investigated by split Hopkinson pressure bar（SHPB）technique and fractal theory,the influence of negative temperature change on dynamic strength performance and deformation law has been analyzed. Combined with the SEM scanning experiment,the microscopic fracture mechanism of saturated frozen red sandstone on the wave propa gation has been studied. It is shown that the negative temperature changes significantly affect the dynamic mechanical properties and the fractal characteristics of red sandstone. The dynamic strength of red sandstone first increases and then decreases with the temperature reduction（from 25 to-40 ℃）,shaped like a＂几＂glyph,however,the peak strain shows a trend of first decreases and then increases,the test results are very different from the static load test results offrozen rock. The fractal dimension of red sandstone at 25,-5,-10,-20,-30,-40 ℃ are respectively 2. 37,2. 12,2.29,2. 35,2. 41,2. 44,and the fractal calculation results are consistent with the test screening results. With the observa tion and analysis of red sandstone fracture morphology,the final fracture of red sandstone at low temperature is found in clay cement or its boundary with mineral particles,red sandstone fracture morphology is relatively complicated under the condition of normal temperature,it is difficult to see the regularity,however,after introducing the low temperature gradient,the fracture morphology of the clay cement and mineral particles gradually show the regularity. It is concluded that the properties and fracture properties of cementitious materials have a more significant influence on the mechanical properties of red sandstone.