Hydrostatic and blast initiated implosion of environmentally degraded Carbon-Epoxy composite cylinders

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The underwater collapse mechanics of environmentally degraded filament-wound Carbon-Epoxy composite tubes were investigated in this study. The composite tubes were submerged in an elevated temperature saline water solution for 35 and 70 days. The temperature of the saline bath was held at 65 °C, in which case the 35 and 70 days duration simulates 3.8 and 7.6 years of service life in accordance with Arrhenius’ equation and a reference temperature of 17 °C. Experiments were performed underwater in a pressure vessel designed to simulate a free-field environment by maintaining constant hydrostatic pressure throughout the collapse event. Two cases of implosion were studied: implosion initiated by increasing the hydrostatic pressure in the vessel until the critical collapse pressure was reached; and by detonating an explosive charge while the composite structure was subjected to 80% of its critical collapse pressure. Three-Dimensional Digital Image Correlation was coupled with high-speed photography to obtain the full-field displacements and velocities of the composite tubes during collapse. Moreover, the pressure fields created during the structural collapse were recorded with tourmaline pressure transducers and coupled with the full-field deformations to analyze the collapse mechanics. Mass saturation was reached during the first 35 days of submergence in the saline water bath. For the implosion initiated by hydrostatic pressure, the composite tubes submerged in the saline water bath displayed different behavior in comparison to the tubes with no exposure. The critical collapse pressure decreased by 20% after 35 days of exposure to the elevated temperature water bath when compared to the non-weathered tubes, and 24% after 70 days of exposure to the elevated temperature water bath when compared to the non-weathered tubes. The full-field data showed that the weathered structures collapsed with higher center-point velocities, which arise from substantial cracking and damage accumulation during the collapse event, as well as lower structural stiffness. The aged composite tubes had a lower overpressure pulse due to an increase in damage. For the blast initiated implosions, the reduced structural stiffness resulted in a quicker instability event. Lastly, further weathering after saturation led to a decrease in structural strength and performance.

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Composite Structures