基于径向变形增量的煤间歇性破坏过程损伤演化分析

Damage evolution analysis of coal during intermittent failure process based on radial deformation increment

煤样单轴压缩条件下常发生间歇性破坏行为,复杂破坏过程的损伤评价有助于明晰伴随该过程的能量演化,对矿业工程灾害预警及防治具有重要意义。为探究间歇性破坏过程损伤演化,对标准煤样进行常规单轴加载,实时监测其变形特征发现,外载荷作用下煤样局部裂隙丛集发生剧烈损伤时,轴向载荷突降,径向变形剧烈增长,且载荷越接近峰值强度,增长速率越快。损伤源于内部裂隙发育扩展,导致试样沿径向快速膨胀,据此提出基于径向变形增量的损伤表征方法,对煤等非均质介质的非线性损伤评价具有更强适用性。对比基于径向变形增量的损伤评价结果与声发射特征及裂隙发育扩展演化,三者高度一致的演化过程佐证基于径向变形评价损伤的可靠性。研究结果表明,间歇性破坏阶段,裂隙局部丛集或者沿最大主应力方向相互连接贯通形成大尺度破裂,试样径向膨胀,局部剧烈破坏导致其损伤变量激增。间歇性破坏行为源于试样内部不同区域反复发生的局部剧烈损伤,锯齿状应力-应变曲线及伴随该过程的非线性损伤演化表明煤等非均质介质在外载作用下存在损伤突变现象。

Intermittent failure behavior often occurs in coal samples under uniaxial compression.The damage assessment of complex failure process is helpful to clarify the energy evolution accompanying the process,which is of great significance to the early warning and prevention of mining engineering disasters.To explore the damage evolution in the process of intermittent failure,the standard coal sample was subjected to conventional uniaxial loading,and its deformation characteristics were monitored in real time.It is found that when severe damage occurs to the local crack cluster of coal sample under external load,the axial load drops suddenly,and the radial deformation increases sharply.The closer the load is to the peak strength,the faster the growth rate is.The damage originates from the development and expansion of internal cracks,resulting in the rapid expansion of the sample along the radial direction.Thus a method of damage characterization based on radial deformation increment was proposed,which is more applicable to the nonlinear damage evaluation of heterogeneous media such as coal.Comparing the damage evaluation based on radial deformation increment with acoustic emission and the development and expansion evolution of fracture,the highly consistent evolution process of the above three proves the reliability of damage evaluation based on radial deformation.The results show that,the cracks are locally clustered or interconnected along the direction of the maximum principal stress to form large-scale fracture in the intermittent failure stage.The radial expansion of the sample causes local severe damage,which leads to a sharp increase in its damage variables.Intermittent failure behavior originates from repeated local severe damage in different areas of the sample.The zigzag stress-strain curve and the nonlinear damage evolution accompanying this process indicate that the damage mutation phenomenon exists in heterogeneous media such as coal under external load.