Dynamic Instability of Anisotropic Cylinders in a Pressurized Limited-Energy Underwater Environment

Abstract

A fundamental experimental study was conducted to understand the physical phenomena resulting from the dynamic instability of carbon/epoxy composite tubes in an underwater pressurized tubular confining environment. The confining nature of the environment limits the potential energy available to drive instability, resulting in a decrease in hydrostatic pressure with the onset of instability and allowing the carbon/epoxy composite tubes to recover. Unsupported tube length and tube diameter were varied in order to determine the effect of tube geometry on the failure mechanisms of the tube and pressure waves emitted throughout the confining chamber during the instability event. High-speed photography coupled with Digital Image Correlation techniques were employed alongside the acquisition of pressure-history data from each experiment to relate specimen displacement behavior to resulting pressure pulses. Tubes of 55 mm diameter experienced partial implosion, in which the walls of the specimen oscillated radially with no wall contact. This resulted in pressure oscillations of the same frequency throughout the confining chamber, with oscillations increasing in amplitude with distance from the axial center. Amplitude of pressure and radial structural oscillations were found to be dependent on pressure just prior to instability. Tubes of 35 mm diameter experienced full implosion, which resulted in water-hammer pressure spikes at the ends of the confining chamber due to the formation and subsequent collapse of large cavitation bubbles. Longer tubes were observed to undergo significantly more damage during full implosion, reducing their ability to recover radially and thus effectively reducing the strength of hammer pulses.