6. Conclusion
Carbon fiber–reinforced vinyl ester unidirectional composite
laminates were characterized after exposure to different marine
environments: Long-term outdoor exposure to UV, sea air and
sea water in a tidal pond; indoor immersion in distilled, salt and
sea water; and indoor exposure to UV radiation, salt spray, and
heat and humidity in accelerated weathering chambers. The study
shows that the effect of different types of exposure on longitudinal
flexural modulus is not significant, though the transverse modulus
has significant decreases. However, flexural strength has been
diminished significantly due to environmental exposures for both
the longitudinal and transverse directions. This can be explained
by the loss in fiber–matrix interface toughness due to moisture
absorption as well as loss in integrity on the surface of laminates
due to extensive UV-induced microcracks, which can synergistically
or individually diminish out-of-plane load bearing capacity
and deteriorate the load transfer mechanism between matrix and
fibers. Comparison between long-term outdoor exposure, indoor
immersion and accelerated laboratory conditions, demonstrated
that 2000 h combined exposure to UV and moisture in environmental
chambers is comparable to one year outdoor exposure in
a tidal pond. Transverse flexural properties of carbon fiber vinyl
ester composites are more sensitive to marine environments compared
to longitudinal flexural properties, since transverse flexural
properties are primarily matrix-dominated which undergo significant
degradation during environmental exposure. Results of the
time-dependent property changes of the CFVE composites exposed
to marine environments is important for design of vessels and
structures used for long durations that may undergo aging due to
exposure conditions, and provides guidelines for the comparison
of laboratory testing conditions to outdoor exposure.