细砂岩裂纹周围变形破坏过程及应变场分布

Fracture development and strain field around the stress induced crack area in sandstone

用扫描电镜实时观测研究了含不同方向预制裂纹的平板状砂岩试件中不同尺度上微破裂的萌生、扩展、集结和连通,以及形成宏观破裂的过程,对一些局部破裂现象进行了实时显微照相。在实验观测的基础上,利用数字图象相关程序对裂纹周围变形场进行了分析计算。研究结果表明:在裂纹开裂过程中,裂纹周围产生较强的应变集中带,其应变值远远超过单轴压缩试验中记录到的平均2％～5％的破坏应变值;而远离破裂带,应变量则低于2％～5％的破坏应变值,说明了岩石试件的破坏过程是一个非均匀的变形分布及传播过程。

Uniaxial compression tests on sandstone samples containing a prefabricated fracture were made. Photomicrographs showing the typical characteristics of the sub-crack development were taken under direct scanning electron microscope (SEM) observation during the test. From these photomicrographs, the direct physical patterns showing the initiation, growth and coalescence of sub-cracks and micro-cracks in sandstone specimen are obtained. Based on the test results, the strain field around the sub-cracks was calculated using the digital image correlation method. The results show that strain concentration which is much higher than the average failure strain around 2-5% for sandstone, occurred close to the crack area. But in far away area, the strain is much lower than 2-5%. Therefore, the crack development in sandstone specimen is a nonhomogeneous deforming process.