数字图像技术在节理岩体裂纹扩展试验中的应用研究

Application of digital image correlation method in experimental research on crack propagation of brittle rock

含倾斜裂纹的岩石在单轴压缩下,会发生翼裂纹扩展并逐步损伤破坏。对含预制裂纹的类岩石脆性试件进行单轴压缩试验,采用两台高分辨率相机连续捕捉图像,经过数字图像相关技术(DIC)处理,得到了试件的全局应变场演化过程图,试验结果表明:当荷载达到一定阶段,裂纹端部观察到了明显的微破裂区,其形状为绕裂纹尖端逆时针转动82°的椭圆;荷载增大到最大荷载的85.6%时,微破裂聚集成核,端部开始形成宏观翼裂纹,裂纹的扩展过程就是高应变区不断蔓延的过程,也是微破裂不断发育、成核的过程;次生微破裂区以及反翼微破裂区发育缓慢,且形成过程中也受到了拉伸应力作用,翼裂纹是试件的主要破坏模式。最后基于线弹性断裂力学,比较了裂纹尖端周围应力和应变的变化规律,给出了采用应变方法分析裂纹起裂扩展的理论依据,并且验证了DIC系统试验结果的可靠性。

Under uniaxial compression, wing crack initiates and propagates in the flawed rock, and the damage evolves. The uniaxial compression tests are carried out on rock-like brittle specimens, each containing a single flaw. Two high-resolution camera are used to capture images to get the global strain fields of the specimens using digital image correlation(DIC)technology. Micro-crack zone is observed obviously at the flaw tip, whose shape is an ellipse with an inclination of 82° with flaw. When the load increases to 85.6% of the maximum load, the micro-crack nucleates, and the macro wing crack initiates at the flaw tip. The cracking propagation is a process of micro-crack development and nucleation, as well as a process of high-strain area spreading. The development of the secondary micro-crack zone and the anti-wing micro-crack zone is very slow. Meanwhile, they are affected by the tensile stress. Therefore, the wing crack is the main crack pattern. Furthermore, the change of stress and strain around the tip is compared based on LEFM. It proves more effective to use the strain approach to investigate crack initiation and propagation. And the reliability of DIC system is verified through theoretical analysis.