SEAWATER EFFECTS ON STRENGTH AND DURABILITY OF GLASS EPOXY FILAMENT-WOUND TUBES AS REVEALED BY ACOUSTIC-EMISSION ANALYSIS/

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 internal hydraulic pr essure. Acoustic emission was used to monitor the damage progression a nd 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 1 4 mechanical conditioning cycles of load and unload prior to performin g a stress rupture test. Both types of tests were performed with as-fa bricated and seawater-saturated tubes to establish seawater effects on damage progression and failure strength. Static moisture absorption d id not have a large effect on the tube strength. In the burst test, se awater saturated tubes only suffered a 6% decrease in their strength. Acoustic emission analysis showed a minor difference between the damag e progression of as-fabricated and seawater-saturated tubes. The combi nation of stress and moisture had a much larger effect on the tubes st udied. During the mechanical conditioning cycles, seawater saturated t ubes exhibited much greater damage accumulation than that exhibited by as-fabricated tubes. As a result the times to rupture for seawater sa turated tubes were much shorter than for as fabricated tubes in subseq uent stress rupture tests.