Structural instability and water hammer signatures from shock-initiated implosions in confining environments

An experimental study is conducted to investigate the dynamic response and instability of cylindrical structures subjected to hydrostatic pressure in conjunction with explosive loading. Full-field displacements/velocities, and localized pressures, of imploding aluminum structures within a confining environment are captured during the experiments. Also, polyurea coatings of 1:1 volume ratios are evaluated as a possible energy mitigation technique. Two high-speed cameras are used to capture the imploding structures while seven dynamic pressure transducers measure the emitted pressure pulses. The specimens are confined inside a thick-walled cylindrical structure that had one end open to the hydrostatic pressure and the other end closed. This confinement configuration generates a water hammer at the closed end of the confinement. The results show that the pressure profiles of the hydrostatic and explosive initiated implosions are about the same after collapse. Moreover, the energy from the implosion's high-pressure pulses, present at the confinement's closed end, was greater than the energy of the explosive itself due to the water hammer effect. The polyurea coatings used in this study caused a sufficient phase shift in the implosion pressures such that the hammer and implosion high-pressure pulses were not superimposed; thus, the maximum pressures and energy after the implosion was reduced. However, the polyurea coatings did not significantly mitigate neither the hammer nor the implosion pressures individually. Finally, a non-linear Riks model from ABAQUS was used to show that the energy input requirement for dynamic-initiated implosions decreases rapidly as initial hydrostatic pressure increases.