高温预损伤下煤岩蠕变声发射及分形特征

Creep acoustic emission and fractal characteristics of coal rock under high temperature pre-damage

为了研究高温条件下煤岩微裂缝发展及破坏规律,对煤样进行不同温度预损伤和三轴蠕变声发射实验,探讨煤岩在经历高温预损伤过后的力学行为特征。研究结果表明:随着温度升高,煤岩预损伤呈幂函数型递增;较低温(≤200℃)预损伤下,煤岩呈脆性破坏特征,加速蠕变特征不明显;较高温(>200℃)预损伤下,煤岩呈韧-脆性破坏特征,且加速蠕变特征较明显;稳态蠕变速率εs的对数值与预损伤D之间呈线性相关关系;温度越高,煤岩的声发射振铃计数率水平越小,呈低频低幅值变化,且蠕变3阶段越趋于"同频"发展,累计振铃计数Nm与预损伤D之间呈负指数型函数递减;分形维数值呈"减小-动态稳定-再次减小"3阶段变化,并与蠕变3阶段相对应,分形维数由稳态向减小转变的转折点可作为判断煤岩失稳破坏的依据;温度越高(预损伤值越大),分形维数df越大,岩样破坏越无序。研究成果对于揭示经历不同温度热解气化损伤后煤岩的长期力学行为具有重要意义。

The thermal damage and triaxial creep acoustic emission experiments of coal samples at different temperatures were carried out to investigate and analyze the mechanical characteristics of coal and rock after high temperature pre-damage.The results show that the thermal damage of coal and rock increases exponentially with the increase of temperature;the brittle-ductile failure characteristics of coal and rock appear at lower temperature(≤200℃)and the accelerated creep characteristics are not obvious;the brittle-brittle failure characteristics of coal and rock appear at higher temperature(>200℃)and the accelerated creep characteristics are more obvious;the value of steady creep rate is between pre-damage D and pre-damage D.The higher the temperature is,the smaller the acoustic emission ringing counting rate of coal and rock is,the lower the low frequency and low amplitude changes,and the three creep stages tend to develop in the same frequency.The cumulative ringing counts Nm and pre-damage D decrease in a negative exponential function.The fractal dimension values change in three stages with creep test,namely,decrease-dynamic stability-re-decrease with the three creep stages.Correspondingly,the turning point of fractal dimension from steady state to decrease can be used to judge the failure of coal and rock.The higher the temperature(the greater the pre-damage value),the larger the fractal dimension df,the more disorderly the failure of rock sample.The research results are of great significance to reveal the long-term mechanical behavior of coal after pyrolysis and gasification at different temperatures.