Search Results (2)

Rocks with multi-shaped fractures in engineering activities like mining, underground energy storage, and hydropower construction are often exposed to environments where stress and seepage fields interact, which heightens the uncertainty of instability and failure mechanisms. This has long been a long-standing challenge in the field of rock mechanics. Current research mainly focuses on the mechanical behavior, seepage, and energy evolution characteristics of single-fractured rocks under hydro-mechanical coupling. However, studies on the effects of multi-shaped fractures (such as T-shaped fractures, Y-shaped fractures, etc.) on these characteristics under hydro-mechanical coupling are relatively scarce. This study aims to provide new insights into this field by conducting hydro-mechanical coupling tests on multi-shaped fractured sandstones (single fractures, T-shaped fractures, Y-shaped fractures) with different inclination angles. The results show that hydro-mechanical coupling significantly reduces the peak strength, damage stress, crack initiation stress, and closure stress of fractured sandstone. The permeability jump factor (ξ) demonstrates the permeability enhancement effects of different fracture shapes. The ξ values for single fractures, T-shaped fractures, and Y-shaped fractures are all less than 2, indicating that fracture shape has a relatively minor impact on permeability enhancement. Fracture inclination and shape significantly affect the energy storage capacity of the rock mass, and the release of energy exhibits a nonlinear relationship with fracture propagation. An in-depth analysis of energy evolution characteristics under the influence of fracture shape and inclination reveals the transition pattern of the dominant role of energy competition in the progressive failure process. Microstructural analysis of fractured sandstone shows that elastic energy primarily drives fracture propagation and the elastic deformation of grains, while dissipative energy promotes particle fragmentation, grain boundary sliding, and plastic deformation, leading to severe grain breakage. The study provides important theoretical support for understanding the failure mechanisms of multi-shaped fractured sandstone under hydro-mechanical coupling. Full article

The spherical pressure hull used in the manned cabin of deep-sea submersibles endures low-cycle fatigue problems during the process of cyclic submergence and recovery, but fatigue testing on its full-scale model is difficult to conduct. To approximate the problem, the paper proposed the design of an L-type equivalent welding joint to simulate the status of the strengthened part of the spherical pressure hull under a certain cyclic axial pressure history. The design principle of the equivalent welding joint is to ensure that the stress ratio between inner and outer surface and the distribution of the simulated test piece should be similar to or smaller than the actual stress distribution characteristics in the critical zone of the spherical hull for conservative consideration. The angle of the L-type joint is 175° in the present study, at which the stress on the outside is at the turning point from compressive stress to tensile stress. The fatigue experiment of the equivalent welding joint is conducted with measurements of crack growth and residual stresses. Multiple cracks are observed in the vicinity of the weld, which grows showing a typical low-cycle fracture morphology. The three-dimensional finite element modelling for the equivalent welding joint with prefabricated notch and the same weld zone shape with its tested piece is carried out. An improved crack growth model proposed by the author’s group, considering multiple factors, is adopted for crack growth calculation and compared with experimental results, which shows satisfactory agreement. The finite element modelling based on the pre-designed L-type joint combined with the improved crack growth rate model can be applied as a simplified method to simulate the fatigue life of the spherical pressure hull. Full article