Moisture-induced degradation of glass/epoxy filament-wound composite tubes

The effect of simulated seawater exposure on the burst strength and stress rupture strength of glass/epoxy filament-wound composite tubes has been examined using hydraulic burst and stress rupture tests. The absorption of 5 wt% simulated seawater during aging prior to testing has a reduction on the burst strength of the tube by 20% compared to unaged composite tubes. Strain gages and acoustic emission techniques were used to monitor the tests. The acoustic emission characteristic is different for the aged tube, giving indications of damage initiation at a much lower level of pressurization. In stress rupture tests, times to rupture of tubes tested in air and tested in simulated seawater immersion were found to be similar. This surprising result is thought to be due to the significant incipient void content introduced during manufacture of the tubes.