Multi-level uniaxial fatigue loading experiments were carried out to reveal the fracture and energy evolution of naturally fractured granite using stress strain descriptions and post-test computed tomography (CT) technique. Results reveal the influence of natural fracture on mechanical properties of granite, regarding the fatigue lifetime, fatigue deformation characteristics, fatigue damage, energy evolution and fatigue failure pattern. Volumetric and shear processes caused by the sliding and shearing along the natural fracture control the whole failure process. The energy dissipation and releases characteristics are strongly impacted by natural fractures. The elastic energy and dissipated energy both decrease with increasing natural fracture volume, growth of the dissipated energy becomes faster for rock near to failure. Post-test CT scanning reveals the crack pattern, and failure changes from tensile mode to shear mode with the increasing natural fracture volume. It is proved that the dissipated energy is mainly used to activate the pre-existing natural fractures.
Real-time acoustic emission (AE) monitoring combined with post-test 3D computed tomography (CT) technique was employed to reveal the rock bridge fracturing behaviors of pre-flawed granite. Results show that the structural deterioration of rock bridge is strongly influenced by dynamic loading frequency. The strength, deformation, and fatigue lifetime of the pre-flawed granites are impacted by loading frequency. AE activities in the form of counts and energy increase with increasing loading frequency. In addition, AE spectral frequency analysis reveals six kinds of crack type, and the proportion of high frequency-high amplitude signal decreases, indicating that large-scaled cracks are prone to forming under high dynamic frequency. Moreover, post-test CT scanning visualizes fracturing pattern of rock bridge, a most striking finding is that complex crack network forms under high loading frequency. It is suggested that flaws are easy to be communicated for rock that subjected to low dynamic loading frequency conditions.
Real-time acoustic emission (AE) monitoring combined with post-test 3D computed tomography (CT) technique was employed to reveal the fracture evolution behaviors of pre-flawed granite. Results show that the dynamic loading frequency impacts the strength, deformation, AE pattern, rock bridge fracturing and fatigue life of the granite samples. The accumulative AE count/energy increases with increasing loading frequency. In addition, AE spectral frequency analysis reveals six kinds of crack type, and the proportion of high frequency-high amplitude signal decreases indicating that large-scaled cracks are prone to form under high loading frequency. By post-test CT scanning visualization of the rock bridge segment, the most striking finding is that complex crack network forms under high loading frequency. The flaws are easy to be communicated for rock that subjected to low dynamic loading frequency conditions. It is suggested that deterioration of the rock bridge is strongly impacted by the dynamic loading frequency.
This work aims to investigate the anisotropic fracture and energy dissipation characteristics of marbles cored along an angle of 0°, 30°, 60° and 90° with respect to interbed planes, subjected to multi-level cyclic loading conditions. Rock fatigue deformation, strength, lifetime and dissipated energy first decreases and then increases with increasing interbed orientation, they get to the minimum for sample having 30° interbed orientation. Rock stiffness degradation is significant with the increase of cyclic level and the stiffness evolution is affected by interbed structure. The incremental rate of dissipated energy becomes faster with increase of cyclic loading level and it presents an abrupt increasing trend at the last cyclic loading level. A damage evolution model was first established based on the dissipated energy to describe the two-phase damage accumulation characteristics. It suggests that the proposed model fits well to the testing data and favorably represents the non-linear characteristics of damage accumulation.
This work aims to investigate the fracture evolution of granite containing two pre-existing flaws under uniaxial increasing-amplitude fatigue conditions using GCTS 2000 rock mechanical system and post-test 3D computed tomography (CT) technique. The impacts of flaw arrangement (i.e., approach angle of 20°, 50°, and 70°) on the stress strain responses, hysteresis loop shape, damage evolution and crack coalescence pattern at rock bridge segment were investigated. Results show that rock structure has obvious impact on macroscopic stress strain responses, volumetric strain, resilient modulus and damping ratio. The sparse-dense pattern of hysteresis loop is different at each loading stage caused by the differential accumulative damage. The resilient modulus decreases and damping ratio increases with increasing fatigue loading stage as damage grows. Post-test 3D CT visualization reveal a most striking finding that crack coalescence is easy for rock having low approach angle, and complex crack network forms for rock having high approach angle.