类岩石材料三维裂纹传播规律试验研究

Experimental study of 3D crack propagation characteristics in rock-like materials

对含有预制三维裂纹的脆性类岩石材料进行了单轴加载试验,结合声发射实时监测及静态CT检测技术,研究三维裂纹声发射特征及传播破裂规律。试验结果表明：试件单轴强度、起裂强度、起裂位移随裂纹深度增加而减小,对于深裂纹试件,剪切裂纹与次生裂纹的传播扩展是试件破坏失稳的关键,破坏形式以剪切破坏为主,并出现沿裂纹延伸方向的横向破断;Ⅰ型破坏起裂导致应力-应变曲线出现阶梯状波动,AE信号出现峰值,破裂后回落到峰前水平,裂纹稳定传播,Ⅱ型破裂起裂能量为Ⅰ型破裂的8~10倍,起裂后AE信号突变式增长;试件内部拉伸裂纹以裂纹中心线为对称轴向两端传播,整体形成反对称向外扩展花瓣形结构,半圆形部分拉伸裂纹起裂角度随着裂纹深度的增加而增大,剪切裂纹、次生裂纹大量发育,预制裂纹尖灭后形成了沿预制裂纹方向横向剪切裂纹面。

A series of uniaxial compression tests is carried out on the rock-like brittle specimens with pre-existing three-dimensional（3D） cracks. Acoustic emission（AE） monitoring technique and computerized tomography（CT） scan are used to investigate characteristics of crack propagation. It is found that the uniaxial compressive strength, crack initiation stress and displacement decrease with the increase of the crack depth in the specimens. The propagation of shear cracks and secondary cracks is the key factor to control the failure of specimens with a deep crack. The main failure mode is shear failure accompanied with transverse fractures. The initiation of Mode-Ⅰ can leads to occurrence of turning points on stress-strain curves while the AE energy reaches a peak value. After crack initiation, the AE energy drops to original level, and remains constant. The AE energy of Mode-Ⅱ crack initiation is 8-10 times higher than that of Mode-Ⅰ. The wing cracks in the loading process forms an anti-symmetrical shape with the crack center line being the symmetry axis. The initiation angle of the wing crack increases gradually with the crack spreading into the specimen. The propagation shape of wing cracks is leaf-like with an anti-symmetrical structure. A large amount of shear cracks and secondary cracks are observed in rock-like specimens. Shear crack plane is initiated towards the extension direction of pre-existing cracks until the pre-existing crack is terminated.