脆性类岩石材料边缘裂纹扩展规律试验研究

Experimental study of edge-opened cracks propagation in rock-like materials

为研究脆性岩石边缘裂纹扩展规律,以自制的类岩石材料试件为研究对象,采用单轴加载、声发射监测及FRACOD^2D数值模拟相结合的方法,对预制边缘裂纹的起裂、扩展及声发射特征进行了研究。试验结果表明:随着预制边缘裂纹宽度的增加,试件的起裂强度、单轴抗压强度逐渐减小,I型拉伸裂纹出现的时间越来越早,剪切裂纹出现的时间越来越晚;试件的破坏形式不因预制边缘裂纹宽度不同而改变,最终以拉伸破坏为主。声发射监测中,裂纹起裂和试件整体破坏时声发射具有阶梯状波动、能量高的特点;边缘裂纹宽度越大,第1次出现能量峰值时间越早;I型破坏产生在线弹性阶段,大多数剪切与次生裂纹产生在峰值强度附近,其能量水平远大于拉伸裂纹起裂点能量值。数值模拟试验过程中,随着裂纹宽度增加,裂纹起裂角度越趋近于加载方向,裂纹数目增多,总位移由4.7 mm降低到1.07 mm,最大拉应力由58.2 MPa减小到26.8 MPa,试件的破坏形式与力学试验相同。

A series of uniaxial compressive tests were carried out on rock-like brittle specimens with pre-existing edge-opened cracks to investigate crack propagation characteristics using the method of uniaxial loading,AE monitoring technique and FRACOD^2D simulation technology.The results showed that the uniaxial compression strength and crack initiation stress both decrease with the increase of the crack width into the specimens.But the occurrence time of mode I tensile crack was more and more early,and that of shear crack was more and more late with the increase of the crack width into the specimens.The failure mode of the specimens didn't change due to the different width of the pre-existing edge-opened cracks,and the ultimate failure modes were tensile failure.AE had the characteristics of step wave and high energy when crack initiation and overall failure of the specimen.With the increase of edge crack width,the time of the first energy peak was earlier.Most of the shear and secondary cracks occurred near the peak strength,and their energy levels were much higher than that of the tensile crack initiation point.The crack initiation angle was closer to the loading direction,the number of cracks increased,the total displacement decreased from 4.7 mm to 1.07 mm,and the maximum tensile stress decreased from 58.2 MPa to 26.8 MPa with the increase of the crack width.The failure modes of the specimens in the numerical simulation were the same as those in mechanical tests.