多级动静载下煤岩力学特性及破裂演化研究

    Mechanical properties and fracture evolution of coal rock under multistage dynamic and static loads

    • 摘要: 煤柱在工作面回采过程中会受到超前支承压力和多次顶板周期断裂动载的复合作用。为探究煤岩在复杂应力环境下的力学响应及损伤破裂机制,开展了搭载数字图像相关(Digital Image Correlation,DIC)技术和声发射监测的动静载力学试验,研究了不同动载幅值和频率下煤样应力应变行为和裂隙演化规律。研究结果表明:随着动载幅值的增加,煤样在动静载作用下的峰值抗压强度相比单轴抗压强度显著降低,最大降幅达到45%;动载频率的降低也可能导致试样强度的进一步下降;弹性模量随动载级数的增加呈现先升后降的趋势,且声发射振铃计数受控于动载幅值和频率。通过DIC技术定量表征试件破裂变形局部化,发现试样在宏观破裂前局部错动和张拉位移会发生突变,同时最大主应变局部化带的错动与张拉位移在动静载过程中呈现不同的波幅特征。

       

      Abstract: During the mining process of a working face, coal pillars are subjected to the combined effects of advanced support pressure and dynamic loads caused by periodic roof fracturing. To investigate the mechanical response and damage fracture mechanism of coal bodies under complex stress environments, dynamic and static loading mechanical tests equipped with digital image correlation (DIC) technology and acoustic emission monitoring were conducted. These tests examined the stress-strain behaviors and crack evolution laws of coal samples under different dynamic load amplitudes and frequencies. The research results indicate that as the amplitude of dynamic loading increases, the peak compressive strength of coal samples under static-dynamic loading conditions significantly decreases compared to the uniaxial compressive strength, with a maximum decrease of 45%. Additionally, a decrease in the frequency of dynamic loading may also lead to a further decline in sample strength. Furthermore, the study found that the elastic modulus initially increases and then decreases with the increase in the dynamic loading level, and the acoustic emission ring-down count is controlled by the amplitude and frequency of dynamic loading. Through quantitative characterization of the localization of fracture deformation in specimens using digital image correlation (DIC) technology, it was found that there are abrupt changes in local dislocation and tensile displacement before macroscopic rupture of the samples. Meanwhile, the dislocation and tensile displacement of the localized band with the maximum principal strain exhibit different amplitude characteristics during the static and dynamic loading processes.

       

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