Multi-dimensional non-uniform deformation and failure of siltstone determined using acoustic, 3D-digital image correlation, and computed tomography

Abstract

Uniaxial compression tests monitored using linear variable differential transformers (LVDTs), digital image correlation (DIC), computed tomography (CT), acoustic emission (AE), and ultrasonic velocity were utilized to study the multi-dimensional non-uniform deformation and failure characteristics of siltstone. Under one-dimensional (1D) conditions, the characteristic stress of the siltstone was determined by the AE counts, ultrasonic velocity, and volumetric strain measured by the extensometer. Under two-dimensional (2D) conditions, zonal disintegration was observed on the apparent fracture of the siltstone specimen. The crack nucleation process, stress release characteristics, and crack type were analyzed in the “broken area,” “penetrating crack area,” and “non-penetrating crack area” under different characteristic stress states. Subsequently, the evolution of the non-uniformity coefficient of the 2D strain field with the 1D characteristic stress was established. Under three-dimensional (3D) conditions, the fracture size of the siltstone was divided according to the equivalent length of fracture volume, and the spatial distributions of macro-, meso-, and microfractures were analyzed. The siltstone 3D zonal disintegration phenomenon was further quantitatively described by calculating the fractal dimensions of fractures in different radius ranges. Finally, the AE source localization method was improved by modifying the wave velocity. The transformation of the primary and secondary bearing areas in different stress stages was revealed based on the spatio-temporal evolution of the AE sources with different energy levels.