Visualization and simulation of rock specimen fracture processes using micromechanics tests

用细观力学试验研究了岩石试件中裂纹扩展和结构复杂性对岩石强度的影响。该试验是在显微镜平台上用小试件(5×6×1 mm)进行加载试验。这种测试的好处是，它很容易描绘出岩石样品的岩石成分的结构形态。还可以很容易地看到穿过试件的裂纹的扩展。在进行细观力学测试后，利用离散元方法(DEM)对实验数据进行了断裂模拟，得到了以下显著结果：1.从花岗岩块体上沿三个方向(H、G和R)制备了小试件。显微镜观察显示，每个试件都具有预先存在的裂纹的主导取向。拉伸强度和应变在H试件中最高，在R试件中最低，从常规拉伸试验的结果也可以看出这一点。2.细观力学测试的拉伸强度值比常规拉伸试验的值小约17%。3.裂纹扩展的可视化表明，饼状裂纹的存在是R试件拉伸裂纹扩展的开始。在G和H样品中剪切裂纹在断裂前滑移。4.黑云母中结构的复杂性影响了花岗岩样品的抗拉强度。也就是说，复杂性指数越高，如黑云母轮廓的分维值越高，抗拉强度就越小。5.含PIE裂纹的三维试件模型的DEM断裂模拟表明，H、G和R试件的拉伸强度及其应变趋势相似。6.断裂过程和破碎过程取决于模型试件中预先存在的裂纹的取向。

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.