关键词: 砂岩, 高温作用, 声发射, 多重分形, 裂纹应力

Abstract: 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 0.2σ_c 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.

Key words: sandstone, high temperature, acoustic emission, multifractal, crack stress