Fracture Response of Externally Flawed Cylindrical Shells to Internal Gaseous Detonation Loading

Experiments were performed to observe the fracture behavior of thin-wall and initially-flawed aluminum tubes to internal gaseous detonation loading. The pressure load, with speeds exceeding 2 km/s, can be characterized as a pressure peak (ranging from 2 to 6 MPa in these experiments) followed by an expansion wave. Flaws were machined as external axial surface notches. Cracks ran both in the upstream and downstream directions as the hoop stress opened up the notch. Different kinds of crack propagation behavior were observed for various loading amplitudes and flaw sizes. For low-amplitude loading and short flaws, cracks tend to run in a helical fashion, whereas for high-amplitude loading and long flaws, cracks tend to bifurcate in addition to running helically. Unless the cracks branched and traveled far enough to meet, resulting in a split tube, they were always arrested. Strain gages were used to monitor the hoop strains at several places on the tubes’ external surface. Far away from the notch, tensile vibrations were measured with frequencies matching those predicted by the steady-state Tang (1965) and Simkins (1987) models. Near the notch, compressive strains were recorded as a result of the bulging at the notch. Features in the strain signals corresponding to different fracture events are analyzed. Nomenclature E Young’s modulus N/m G shear modulus N/m R shell mean radius m h shell thickness m l shell length m Pcj Chapman-Jouguet pressure Pa Ucj Chapman-Jouguet velocity m/s v shock speed m/s vd dilatational wave speed m/s β shell thickness parameter ∆p pressure difference across shell Pa κ shear correction factor ν Poisson’s ratio ρ density kg/m KIc Mode-I fracture toughness MPa √ m σ stress N/m d initial notch depth m 2a initial notch length (model) m L initial notch length (experiment) m