Seawater Effects on Strength and Durability of Glass/Epoxy Filament-Wound Tubes as Revealed by Acoustic Emission Analysis

Abstract

The effect of seawater on the strength and durability of glass/epoxy [90 3 /±25/90 3 ] filament-wound composite tubes was investigated by testing tubes in the closed-ended test mode with intemal hydraulic pressure. Acoustic emission was used to monitor the damage progression and to interpret seawater effect. Two types of tests were performed. In the burst test, the tube was pressurized monotonically at a constant rate to failure. In the second type of test, tubes were subjected to 14 mechanical conditioning cycles of load and unload prior to performing a stress rupture test. Both types of tests were performed with as-fabricated and seawater-saturated tubes to establish seawater effects on damage progression and failure strength. Static moisture absorption did not have a large effect on the tube strength. In the burst test, seawater saturated tubes only suffered a 6% decrease in their strength. Acoustic emission analysis showed a minor difference between the damage progression of as-fabricated and seawater saturated tubes. The combination of stress and moisture had a much larger effect on the tubes studied. During the mechanical conditioning cycles, seawater saturated tubes exhibited much greater damage accumulation than that exhibited by as-fabricated tubes. As a result, the times to rupture for seawater saturated tubes were much shorter than for as-fabricated tubes in subsequent stress rupture tests.