Dynamic Viscoelastic Properties and Time-Moisture Superposition of Moistened Unidirectional CF/Epoxy Composites

We have investigated the behavior of moisture absorption by a unidirectional CF/epoxy composite stored in a chamber, which can separately control temperature and humidity in air, and examined the effect of moisture on the dynamic viscoelastic behavior of CFRP. The moisture absorption behavior was confirmed to obey the Fick's law of diffusion. The dynamic viscoelasticity of specimen generally shifted to that at lower temperature, as an effect of plasticisation. The glass-transition temperature (Tg) of CFRP was lowered with increasing water content, and the reduction in Tg of moistened specimen was always greater than that of water-soaked specimen. The time-moisture superposition was confirmed to hold in air at various relative humidities at 60°C.