Visualization and simulation of rock specimen fracture processes using micromechanics tests

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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.