Dynamic fracture response of pre-flawed elbow pipe subjected to internal hydrogen-oxygen detonation

Abstract

A coupled fluid-structure-fracture approach was presented to study the dynamic fracture of pre-flawed elbow pipes subjected to internal hydrogen-oxygen detonation. The initial flaw is located at the extrados, crown and intrados of the elbow, respectively. The hydrogen-oxygen detonation was modeled by a user-programed burn method based on the CJ theory. The fracture of elbow pipe was simulated by a validated bivariate failure criterion which was deduced based on the adiabatic shear failure mechanism of materials at high strain rates. Results demonstrate that the presented approach can capture the detonation wave propagation and the complex crack extension and branching effectively. It is found the peak pressure at extrados is 2.9 times larger than that at intrados, but the hoop stresses and effective strains at the three initial flaw positions are comparable with each other, even the average amplitude of hoop stress at intrados is higher than those at extrados and crown. The increase of detonation pressure can lead to crack branching and makes more cracks propagate simultaneously. The crack initiating at crown tends to turn and run to the intrados when passing the transition sections of elbow, while the crack initiating at intrados is expected to branch here. The average crack speeds for forward cracks are 100–300 m/s, while the speeds are 70%–90% of the above for backward cracks. The branch crack speeds are generally less than 40% of those before branching. Furthermore, the elbow pipes with initial flaw at intrados generally have the largest total crack length, while elbow pipes with initial flaw at crown have the strongest resistance against crack propagation. It is also suggested that local bucking is an important feature that takes place in dynamic fracture processes of elbow pipes.