单轴压缩下三维裂纹扩展机理试验与离散元分析

Experimental and DEM Analysis on 3-D Crack PropagationMechanism under Uniaxial Compression

为了加强对三维裂纹扩展机理的认识,采用一种脆度良好的树脂材料制作含预制三维双裂隙的试样,并基于离散元理论,研究在单轴压缩条件下平行双裂隙的扩展、搭接和贯通机理,同时设置测量圆来监测在不同加载阶段模型的应力场变化。研究结果表明:预制裂隙长轴端部C1-E和C2-W萌生的翼裂纹沿垂直裂隙平面方向扩展至一定长度后会保持长时间不变,直到应力达到峰值附近才继续沿着最大主应力方向扩展;在峰值应力附近时,预制裂隙端部C1-W和C2-W的花瓣状翼裂纹和反翼裂纹才相互搭接贯通形成空间卷曲面;随着轴向应力增加至峰值附近,最大主应力主要分布在远离预制裂隙的区域,而压应力却集中在预制裂隙中心区域,因此抑制了翼裂纹的进一步扩展;最大压应力和切应力随着应变增加而增加,最大拉应力却在峰值应力附近发生了跌落,说明在加载后期,裂纹扩展主要受压剪作用力控制。

For a better understanding of the evolution mechanism of 3-D crack propagation in brittle rock mass,the mechanism of 3-D crack propagation,coalescence and overlap in rock-like materials(a newly developed resin)with pre-existing double flaws under uniaxial compression is investigated based on the discrete element theory.Meanwhile,measurement circles are employed to monitor the variation of stress field of the model at different loading stages.The results reveal that wing cracks initiated from the long shaft ends of the pre-existing flaws C1-E and C2-W propagate towards the vertical direction of flaw plane to a certain length and then remain unchanged for a long time,and continue to propagate along the direction of the maximum principal stress when the stress reaches the peak.When axial stress reaches around the peak,petal-like wing cracks and reverse-wing cracks at the ends of the pre-existing flaws C1-W and C2-W coalesce and form a curling surface.As the axial stress increases to the vicinity of the peak,the maximum principal stress is mainly distributed in areas away from the pre-existing flaws,while the compressive stress is concentrated in the central region of the pre-existing flaws,thus imposing restrictions on the further propagation of the wing cracks.The maximum compressive stress and shear stress increase with the increasing strain while the maximum tensile stress drops near the peak stress,indicating that the crack propagation is mainly controlled by the compressive shear force in the later stage of loading.