Moisture effect on shape distortions of curved quasi-isotropic prepreg composite laminates

Abstract The influence from moisture on shape distortion of curved thermoset composite laminates is investigated experimentally. The objects of study are L-shaped carbon/epoxy specimens with a quasi-isotropic layup and a thickness varying between 1 and 12 mm. The effect on the shape distortion is quantified by means of angle measurements vs. accelerated moisture uptake utilising a climate chamber at 90°C and 95% relative humidity. The results show a strong dependence from laminate moisture content – the effect is in fact in the same order of magnitude as the spring-in from thermal and chemical shrinkage during curing. Moisture does thus not only affect the spring-in angle but also has to be taken into consideration, and be carefully controlled, when assessing shape distortions due to other parameters. Finally, a closed form expression based on the experimental results is presented, predicting how the bracket angle varies with the specimen thickness and moisture content.