复合应力状态下砂岩损伤演化与裂纹扩展特征试验研究

Experimental study on damage evolution and crack propagation characteristics of sandstone under combined stress state

为从细观尺度上研究复合应力状态下岩石中裂纹的扩展,采用数字图像相关技术,对砂岩人字形切槽巴西圆盘试件展开试验研究。基于试验中获取的试件在加载全程中的裂缝开口位移、全场域的应变场和位移场的分布和演变规律,对岩石的损伤演化及裂纹扩展机制和特征进行分析。结果表明:复合应力状态下岩石的损伤演化具有明显的阶段性;主要断裂形态为翼裂纹和次生裂纹,均为拉剪复合型裂纹;翼裂纹起裂位置随加载角度增大向试件中心靠近,沿曲线路径向加载点扩展,扩展中主导机制为拉伸;次生裂纹从柱面边缘起裂,以较平直路径向切缝尖端或切缝上某处扩展,扩展过程快速而不稳定,拉伸与剪切在其扩展机制中所占比重随加载角度变化。

In order to study crack propagation mechanism in rocks under combined stress state in meso scale,experiments were conducted on cracked chevron notched Brazilian disc(CCNBD)sandstone specimens using the digital image correlation technique.Based on the distribution and evolution of crack mouth open displacement,strain and displacement fields obtained from experiments under different combined stress states,the mechanisms and characteristics of damage evolution and crack propagation of sandstone specimens were investigated.It is shown that the damage of CCNBD sandstone specimens evolves obviously through similar stages for all the different combined stress states;that the main fracture modes are wing cracks and secondary cracks,both of which are tensile-shear mix-mode cracks.With the increase of the loading angle,the initiation location of wing cracks moves towards the center of specimens and approaches the loading point along a curved path with tensile as the dominant mechanism.The secondary cracks,originating from the circumferential edge and approaching the tip of the notch or an arbitrary location on the notch along a relatively straight path,propagate in a fast and unstable manner and the proportion of tensile and shearing in the propagation mechanism changes under different loading angles.