Flaw Combination Research Articles

Mechanical behavior of rock-like specimen containing hole-joint combined flaw under uniaxial loading: findings from DIC and AE monitoring

Holes and joints are widespread and coexisting flaws in natural rock. The spatial distribution of combined flaw significantly affects the instability process of fractured rock. To study the influence of ligament length and joint angle on failure characteristics, uniaxial compression experiments are carried out on specimens containing hole-joint combined flaw assisted by acoustic emission (AE) and digital image correlation (DIC) technologies. As the ligament length increases, the mechanical parameter curves decrease first and then rise, showing a U-shape or V-shape. DIC results show that the hole performs a strong inhibition on the crack propagation from the inner joint tips, which will be weakened with the increase of ligament length. The driving displacement field of wing cracks and the type of cracks outside the joint are affected by joint angle variation. The cracks in rock bridge area are generally tensile-shear or shear type. According to AE analysis, the proportion of tensile signals decreased from the pre-peak failure stage to the post-peak stage, and the tensile signal is lower than 50% in the late loading stage, indicating that the shear crack dominates the final failure of specimens.

Cracking Process and Stress Field Evolution in Specimen Containing Combined Flaw Under Uniaxial Compression

Hydraulic slotting, an efficient technique for underground enhanced coal bed methane (ECBM) recovery, has been widely used in China. However, its pressure relief mechanism is unclear. Thus far, only limited research has been conducted on the relationships among the mechanical properties, flaw parameters, and crack propagation patterns of coal after hydraulic slotting. In addition, because of the limitations of test methods, an in-depth information is not available for this purpose. In this work, numerical models of specimens containing combined flaws are established based on particle flow code method. Our results provide insights into the effects of flaw inclination angle on the mechanical properties, crack propagation patterns, and temporal and spatial evolution rules of stress field in specimens containing combined flaws during the loading process. Besides, based on the initiation position and underlying mechanism, three types of crack initiation modes are identified from the failure processes of specimens. Finally, the crack propagation pattern is quantitatively described by the fractal dimension, which is found to be inversely proportional to the uniaxial compressive strength and elastic modulus of the specimen. To verify the rationality of the numerical simulation results, laboratory tests were conducted and their results match well with those obtained from the numerical simulation.

Corrosion Degradation Behavior of Alumina Ceramics in Hot Sulfuric Acld

Corrosion behavior of 93wt% alumina ceramics was investigated. The weight, the bending strength and the thickness of corroded layer were measured after exposed in sulfuric acid at temperatures of boiling point and 90°C. The weight decreased with time, but the weight loss rate became small. On the contrary, the thickness of corroded layer, which was determined by a porous zone depth formed on the surface of secimens as a result of dissolution of grain boundary phase, increased linearly with time. The bending strength decreased with an increase in the corroded layer depth. However, the morphology of fracture was inconsistent with the assumption that the corroded layer depth corresponds to a flaw dimension causing the failure. As large numbers of pore were observed on the fracture surface of the specimens, it was suggested that a combined flaw of the pore and the corrosion layer governs the strength of corroded alumina.