Venizelov, Greenshields, Leevers
Additional Information - Posters # 1995 Edinburgh
An analytical I-D model of the gas discharge process in the small scale steady State ( ~ 4 ) test for rapid g a c k propagation (RCP) in thermoplastic pipe has been developed. Because the gas can exert a powerful crack driving force, such a model is essential to an understanding of the test. This model yields a closed-form analytical expression for the pressure decay behind the crack tip, as a function of distance, crack velocity and crack opening angle (COA). It is based on the primary assumptions that the discharge process is predominantly radial, and the gas flow velocities inside the rupturing pipe are negligible. The former is due to suppression of axial decompression in the S4 test and the latter due to crack openings considerably smaller than those observed during RCP in ductile steel pipes. Both assumptions are based on experimental and numerical evidence. The only uncertainty in the model is the unknown relationship between crack speed and crack opening angle. Using values of C O A based on evidence from fast photography, and assuming a linearly decreasing dependence of COA on crack speed, very good correlation between model and experiment has been achieved. This model should prove to be a valuable tool for the efficient formulation of a "coupled" RCP numerical model of the s4 test (in which the behaviour of both the structure and the fluid as well as their interaction is considered) since it eliminates the need for numerical solution of the fluid dynamics.