Visualization and simulation of rock specimen fracture processes using micromechanics tests

通过细观力学试验研究岩石试件的裂纹扩展规律，探讨结构复杂性对岩石强度的影响。该测试是在显微镜台上使用小样本进行的加载测试（5×6×1mm）。这种测试的好处是，它很容易描绘岩石样品的岩石成分的结构形态。通过试样的裂纹的生长也很容易可视化。在细观力学试验后，利用所得数据进行离散元法（DEM）断裂模拟。得到了以下显著结果：在花岗岩块上按H、G、R三个正交方向制备小试件。微观观察表明，每个试样都有一个主导方向的预先存在的裂缝。常规拉伸试验结果也表明，H试样的抗拉强度和应变最高，R试样的抗拉强度和应变最低。微力学试验的拉伸强度值比常规拉伸试验的强度值小约17%。裂纹扩展的可视化表明，在R试样中，饼状裂纹是拉伸裂纹扩展的开始。在G和H试样中，剪切裂纹在破裂前发生滑动。黑云母结构的复杂性影响了花岗岩试样的抗拉强度。即复杂指数越高，如黑云母轮廓的分形维数越高，则抗拉强度越小。对含裂纹的三维试件模型进行DEM断裂模拟表明，H、G、R试件的细观力学试验得出了相似的抗拉强度及其应变变化趋势。断裂过程和破碎程度取决于模型试样中预先存在裂纹的方向。

A micromechanics test was carried out to elucidate crack growth and investigate the influence of structural complexity in rock specimens with rock strength. That test is a loading test on a microscope stage using small specimen (5×6×1mm). Benefits of this test are that it readily depicts the structural configuration of rock components of rock specimens. It is also easy to visualize the growth of cracks passing through the specimen. After micromechanics tests, fracture simulations using discrete element method (DEM) were conducted using obtained data.The following salient results were obtained :1.Small specimens were prepared from a granite block in three orthogonal directions (H, G and R). Microscopic observation showed that each specimen had a dominant orientation of pre-existing cracks. Tensile strength and its strain were highest in the H specimen and lowest in the R specimen, as shown also by results obtained from usual tensile tests.2.Tensile strength values from micromechanics tests are smaller by about 17% than those from conventional tensile tests.3.Visualization of crack growth shows that a pie-existing crack is an onset of tensile crack growth in the R specimen. The shear crack slides before rupturing in G and H specimens.4.The complexity of the configuration in black-mica influenced the tensile strength of the granite specimen. That is, the higher the complexity index becomes, such as that of the fractal dimension of the black-mica outline, the smaller the tensile strength is.5.Fracture simulation of DEM for a 3D specimen model including pie-existing cracks shows that a similar tendency of tensile strength and its strain are obtained from micromechanics tests for H, G, and R specimens.6.The fracture process and fragmentation differed depending on the orientation of pre-existing cracks in the model specimens.