Moisture in Composites: The Effect of Supersonic Service on Diffusion

Tests were conducted to determine whether aircraft flight conditions change moisture absorption behavior in graphite-epoxy composites. Flight temperature profiles were simulated for a subsonic mission, -65°F (-54°C) for 90 minutes, and for a flight involving a subsonic segment with a supersonic dash. The simulated dash involved rapid heating to a peak of 300°F (149°C) followed by rapid cooling. These simulated dashes or thermal spikes caused small, temporary drying effects. However, they also caused permanent changes in the subsequent moisture diffusion behavior of the graphite-epoxy. Both the amount and rate of moisture absorption were significantly increased. Subsonic temperatures, however, caused no detectable change in diffusion behavior.