Dynamic fracture is one of the most important challenges facing the pipeline industry. This phenomena can lead loss of revenue and life. Because of expensive experimental tests, analytical and numerical simulations are preferred. Most instances, dynamic fracture mechanics analyses of structural components can safely assume that the external loads are independent of the crack propagation and arrest event. However, for pressure vessels and pipelines this will not always be the case. Here the flow of the contained medium through the crack opening can play a significant role in dictating the crack driving forces. Rapid crack propagation along the axial direction of a gas pipeline is an important typical case. Accordingly the high degree of interaction between the escaping gas and the pipe wall deformation should be considered to obtain exact and reliable results. The main aim of this study is to simulate and analyze stationary cracks using Fluid-Solid Interaction (FSI) method. For this purpose a coupled fluid–structure modeling methodology for pressurized pipelines has been developed. The pipe material have been modeled using the finite-element method with a ductile fracture criterion. The finite-volume method has been employed to simulate the fluid flow inside the pipe, and the resulting pressure profile behind the crack tip, which is the main source of the crack driving force, was computed and applied as a load in the finite-element model. Choked-flow theory was used for calculating the flow through the pipe crack. The study involves three major parts. In the first part the deformation and stress field surround the elliptical notch due to escaping of the high pressure gas, is simulated using 2-way FSI method. In the second part a new approach is developed for analyzing of a stationary crack parameters due to escaping of the gas by combining a 1-way FSI simulation and try and error method. The parameters like dynamic stress intensity factor(K I ), stress field in the front of the crack tip and plastic zone was computed using this new approach. It is assumed that the initial crack is parallel to the pipe axis. Finally in the third part, the results of previous parts are validated by comparison to two experimental tests. The first test which was found in literature, studies aluminum 6061-T6 tube and the other one was been done in the present study using a hyper elastic tube. The very promising results have been obtained. Keyword : High pressure gas transmission pipelines, Dynamic fracture, Stationary crack, Fluid-structure Interaction(FSI), Dynamic stress intensity factor.
