Onnagawa shale samples are deformed through the brittle-ductile transition by increasing the confining pressure. Brittle deformation is characterized by longitudinal splitting of the sample at 3% axial strain. A distributed conjugate fracture network characterizes the macroscopic deformation in the ductile field with strain hardening. The onset of transition from brittle to ductile deformation is between 4% and 5% axial strain with a single shear plane defined failure. Deformed samples are scanned in a commercially available X-ray CT machine to investigate the sensitivity of the fracture network to the choice of threshold voxel value. The primary voxel values of the deformed rock are reversed, and their density distribution is approximated by a normal distribution to extract the voxel value density distribution that fabricated the fracture network (residual). Successive thresholding of the residual histogram shows that the generated fracture network is highly sensitive to the choice of threshold. Post peak thresholding of the residual histogram generates voxel volumes of fractures alone and consecutive thresholding shows that the obtained volume segments of the fractures can interpret possible nucleation, growth, and coalescence within the damaged zone. Results further show similarity to previous 4D tomographic strain localization investigations and damage size distributions by acoustic emission studies. Therefore, despite the postmortem nature of the investigation, the new technique opens possibilities to investigate the possible evolution of fracture properties under elevated confining pressures and in the absence of high energy synchrotron facilities.

中文翻译：

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通过 X 射线计算机断层扫描的死后阈值对女川页岩的损伤演化

Onnagawa 页岩样品通过增加围压而通过脆-韧转变变形。脆性变形的特征是样品在 3% 的轴向应变下发生纵向分裂。分布共轭断裂网络表征具有应变硬化的韧性场中的宏观变形。从脆性变形到延性变形的开始是在 4% 到 5% 的轴向应变之间，单一剪切面定义失效。在商用 X 射线 CT 机中扫描变形样品，以研究断裂网络对阈值体素值选择的敏感性。变形岩石的原始体素值被反转，并且它们的密度分布通过正态分布近似以提取制造裂缝网络（残差）的体素值密度分布。残差直方图的连续阈值化表明生成的裂缝网络对阈值的选择高度敏感。残余直方图的峰值后阈值单独生成裂缝的体素体积，连续阈值表明获得的裂缝体积片段可以解释损坏区域内可能的成核、生长和聚结。结果进一步显示了与之前通过声发射研究进行的 4D 断层扫描应变定位调查和损伤尺寸分布的相似性。因此，尽管调查具有事后性质，