Detonation loading of tubes in the modified shear wave speed regime
We performed experiments and numerical simulations on a thin-wall aluminum tube with internal gaseous detonation loading in the modified shear wave speed regime. Strain gauges were used to determine the time-dependent hoop strain on the surface of the tube. The experimental results were compared with analytical models and numerical simulations with explicit finite element computation treating the detonation as a traveling load. Hoop strain amplification factors (defined as the ratio of the dynamic strain to the equivalent static strain) close to two were obtained both in the present experiments and simulations. No resonance phenomena in the hoop strain were found in either experiments or simulations. Computations reveal the existence of a resonance in the shear strain.
Structural response to detonation loading in 90-degree bend
The structural response due to detonation propagation through a 90-degree bend in a circular tube was experimentally examined. Hoop strain measurements were obtained at key locations along the tube to measure elastic deformation. Dynamic pressure signals at the same locations were also recorded to track the detonation wave and record the peak pressure. Of particular interest are the effects of the bend on the magnitude of the pressure and strain in the material when compared to the straight tubes. These geometrical effects are due to the excitation of multiple modes: a short period detonation driven mode and longer period bending modes within the structure not seen in the straight tubes. The excitation of these bending modes serves to increase the maximum strain observed, which translates to greater hazards for industrial piping systems.
A finite element model for crack arrestor design in gas pipelines
Steel rings are frequently used as crack arrestor devices in steel gas transmission pipelines to prevent the possibility of long running axial cracks. These arrestors have the effect of reducing the pipe opening as the crack propagates. This decreases the available crack driving force and, as a result, crack arrest can take place. This essentially is a second line of defence against catastrophic failure in the event that crack initiation cannot always be prevented. This paper describes a novel analysis methodology that has been developed to investigate the suitability of these crack arrestors. This is based on a fluid/structure/fracture interaction package, PFRAC. Here, a curved beam element has been implemented into PFRAC to simulate the behaviour of the arrestor. The contact conditions between the pipe wall and the arrestor, along with the various computational procedures, are described here. Several numerical results for a cracked pipe with arrestors are presented along with comparisons with pipes that do not have arrestors.