Moisture diffusion in composites tubes: Characterization and identification of microstructure-properties relationship

This work aims at highlighting some microstructure-properties relationships; namely: the effect of the microstructure on the diffusive behavior of composites tubes obtained by filament winding technique. Composites tubes are made from either glass or carbon fibers impregnated with the same epoxy matrix cured at 150 degrees C. Specimens were rings cut from tubes. Three winding angles were investigated: +/- 42 degrees, +/- 56 degrees or +/- 78 degrees. Glass and carbon/epoxy tubes present a strongly different void content, respectively, 1.7% and 5.7%. Immersion aging tests were conducted in distilled water at 70 degrees C. Results show that despite both glass and carbon composites are made of the same resin, moisture uptake exhibits strong discrepancies between glass/epoxy and carbon/epoxy samples. An investigation of the most appropriate diffusion model for glass and carbon/epoxy specimens is developed in this paper, based on an experimental study of the microstructure of these composites owing to various complementary characterization methods. Glass/epoxy rings exhibit a Fickian diffusion, whereas carbon/epoxy specimens do not match a Fickian diffusion. A dual-stage Fickian law is discussed and seems to fit quite well in experimental observations.