Transient Moisture Effects in Fibers and Composite Materials

Unlike constant moisture effects on the behavior of composite materials, transient moisture effects are not well studied and known. Armstrong and Kingston have shown that the creep of wood under transient humidity levels could be greatly accelerated over that at any constant moisture content. Later this phenomenon was termed “mechano- sorptive”. In this paper, the authors show that aramid fibers (Kevlar® 29, Kevlar® 49, and Kevlar® 149) and Kevlar® 49/epoxy composites exhibit mechano-sorptive phenomenon. Kevlar® composites were studied using both creep and dynamic mechanical analysis while undergoing desorption. Creep of single Kevlar® fibers was studied during relative humid ity conditions cycled between 5 % and 95 %. The results observed with Kevlar are consis tent with those reported for other natural polymeric materials.