Studies with closed-cell insulations showed that more moisture could be introduced into some types by the influence of a thermally induced moisture vapor gradient than could be accomplished by soaking. A study was performed to see if aramid-wrapped carbon/vinyl ester epoxy samples behaved in the same manner. Aramid-wrapped carbon/epoxy samples were fabricated with exposed fibers at the edges. The samples were subjected to moisture intrusion both by isothermally soaking in water and by introducing them to a thermally induced vapor drive over a 60-day period. The samples were then tested in tension, quasi-statically at 0.05 inches/minute at both room temperature and −30°C. The soaked samples gained over 13 times the percentage of water the vapor-exposed samples did at 10 times the rate. However, the results show small absolute moisture gains by either the soaked or vaporexposed samples. The peak stress, strain, and tangent modulus values also show little difference.
The strength of composite materials can be affected by both temperature and moisture intrusion into th e lay-ups. An area of concern is what happens to composite strength if moisture intrudes into the lay-up and then freezes, possibly breaking the fiber to resin bonds and weakening the composite. The amount of moisture is measured by weight and the strength of the soaked samples is then compared to the strength of dry control samples. Submerging samples is not representative of the environmental conditions that most composites would experience and it may not be the most effective method of introducing moisture into the composites. Composite ship and vehicle compartments are becoming more common where the interior of the space is warm and relatively moist and the exterior may be cold and dry during winter weather conditions.
