MOISTURE ABSORPTION BEHAVIOR OF 3-D CARBON-FIBER-EPOXY COMPOSITES AND EFFECT OF EXTERNAL STRESS

Three-dimensionally (3-D) braided carbon fiber reinforced epoxy resin (C_3D/ER) composites were produced by vacuum impregnation technique. The present study is carried out in order to determine the water absorption characteristics of the 3D composites. In addition, the influences of the external load on the water uptake and changes in the flexural, shear and impact strengths were also determined as a result of moisture absorption. The kinetics of moisture absorption by the stressed and unstressed composites, as well as the unreinforced epoxy resin, was determined for the absorption at 37 ℃±0.5 ℃. The results show that the C_3D/ER composites exhibited a complicated absorption behavior. In contrast to the epoxy resin, the absorption behavior of the C_3D/ER composite could not be described by using Fick's law of diffusion. The results clearly demonstrate the contribution of the external stress to the water absorption behavior and changes in mechanical properties. The external stress was found to increase the moisture content and mechanical properties reduction at earlier stages. At later stages, a contrary trend was observed. It is concluded that the mechanical properties are proportional to their moisture content for the C_3D/ER composites. Mechanisms were proposed to interpret these experimental phenomena.