高温作用下砂岩声发射特征及破坏前兆

Acoustic Emission Characteristics and Failure Precursor of Sandstone in High Temperature

为探究不同温度作用后砂岩声发射多重分形特征及破坏前兆信息,对不同温度加热后砂岩开展室内单轴加载试验,研究试样破坏过程中裂纹起裂应力、损伤应力、峰值应力及声发射特征等的演化规律。试验结果表明:借助声发射技术量化识别了加载过程中不同温度加热后砂岩的裂纹起裂应力和损伤应力门槛,随着温度的增加,不同裂纹应力门槛呈现出先增加后降低的演化规律,裂纹起裂扩展阶段占比逐渐降低。当应力水平由0~0.2σc增至峰后阶段时,多重分形谱宽度呈现出先降低后增加的趋势,该结论进一步证实了加载过程中砂岩内部结构产生的变化。声发射b值总体上呈现出先增加后降低的变化规律,试样失稳破断前声发射b值急剧下降,声发射b值急剧下降阶段可作为失稳突变前兆信息点。

To investigate the multifractal characteristics of acoustic emission(AE)and failure precursory information in thermally-treated sandstone,we conducted indoor uniaxial compressive tests on sandstone samples subjected to different temperatures.We systematically analyzed the evolution of crack initiation stress,damage stress,peak stress,and AE characteristics throughout the failure process.The experimental results demonstrate that AE technology enables quantitative identification of crack initiation and damage stresses in thermally-treated sandstone.With increasing temperature,different crack stress thresholds exhibit a consistent evolution trend,initially increasing and then decreasing.The proportion of crack initiation and propagation gradually diminishes.As the stress level rises from 0.2σc to the post-peak stage,the width of the multifractal spectrum initially decreases and subsequently increases.This observation further confirms the structural changes occurring within thermally-treated sandstone.During the initial loading stage,the AE-b value experiences an initial increase followed by a decrease.Subsequently,as the sample approaches the unstable failure stage,the AE-b value sharply decreases,which can be considered a precursor to the instability fracture of thermally-treated sandstone.