Numerical Simulation For Crack Propagation Process In Spiral Case Structure By The Fracture Mechanics Theory

The embedded spiral case is such a structure that steel lining and surrounding reinforced concrete joint bear the internal water pressure together. Some cracks would appear on the surrounding concrete under the internal water pressure. If considering the pulsation pressure, maximal internal water pressure and other special conditions, the crack may run through the surrounding concrete. The spiral case cracks initially appear inside of the surrounding concrete, which make big difficulty to research the origination and propagation of the crack by experiments. The numerical simulation of the spiral case usually uses the criteria of ultimate tensile strength of the concrete. But the criteria do not consider the stress concentration on the top of the crack. To solve this problem, the article chose the criteria based on the theory of stress intensity factor as the criteria of the crack split by using the fracture mechanics theory of concrete and considering the singularity on the crack tip. The ANSYS APDL language is used to write a program to simulate the crack propagation of the surrounding concrete. To realize the propagation of spiral case crack, this article has completed the following tasks:1. According to the virtual crack model theory of fracture mechanics, the flat stress finite element model of notched three-point bend beam is built. By applying the cohesion in the fracture process, and using APDL language to write the mode I fracture propagation program, the propagation process of four notched three-point bend beam is simulated. Compared the results of numerical and experiment, the reliability of the mode I fracture propagation program was proved.2. Based on the mode I fracture propagation program of notched three-point bend beam, the breaking angle concept is introduced to judge the direction of the mixed mode I-II fracture propagation. The program is amended to simulate the mixed modeâ… -â…¡fracture propagation process. This article simulates the fracture propagation process of a classical four-point shear beam. By compared with the experiment results, it can be shown that numerical results are quite close to experiment result and this program is effective to simulate the mixed mode I-II fracture propagation process.3. Cracks on the surrounding concrete of spiral case belong to the mixed mode I-II crack. By setting a initial crack in the concrete of the spiral case and building a flat axis-symmetric model by virtual crack model theory, this article calculated the fracture propagation process on the surrounding concrete of embedded spiral case by the above programs. The results show that:the virtual crack model theory of fracture mechanics is well suitable to simulate the whole progress of crack propagation in spiral case, and can get the internal water pressure versus crack mouth opening displacement (the width of crack mouth) curve of a single crack. By utilizing the concept of break angle, it could get the accurate way of the spiral case crack propagation, that is, the main orientation of the crack propagation on the meridional cross section of the embedded spiral case is the radial direction.