A novel accelerated moisture absorption test and characterization

Moisture plays a significant role in influencing the mechanical behavior and long-term durability of composites. With the current available testing techniques the time required for environmental qualification of polymer composites can be on the order of several years and any interruption in the test can result in a significant cost and schedule penalty. Because of these long environmental conditioning times there is a strong desire to accelerate the process to advance environmental qualification of materials for use in commercial and military aerospace structures. An accelerated humidity test technique has been developed where moisture ingression was obtained by increasing the pressure in the test chamber. A hygrothermal humidity chamber was used in combination with D2O water to subsequently characterize the diffusion of D2O in a carbon/epoxy composite using Nuclear Reaction Analysis (NRA). Moisture content was also measured as a function of through-thickness depth using NRA. The accelerated technique decreased the time to saturation by 80% as compared to conventional diffusion without pressure. Moisture uptake from both conventional and accelerated diffusion exposures followed typical Fickian diffusion response.