Abstract：K49 and F-Ⅲ two kinds of different structure aramid fibers and their 5224A epoxy matrix composites were selected. The tension strength of single fiber, FTIR, XPS, DSC, SEM,mechanical and dielectrical properties was used to characterize the physicochemical properties of fibers and structure/wave-transmitting properties of composites. It is found that different fibers result in different changes under the same solar radiation condition. The obvious "self-shield" phenomenon is observed in K49 fibers,but there's no proof that F-Ⅲ has the same ability. A tension strength conservation rate of 82% is obtained after 400 hours solar radiation. F-Ⅲ fibers, by contrast, are sensitive to solar radiation and a conservation rate of 50% is obtained at the same condition. The decreased tension strength is due to physicochemical degradation on the surface of the fibers and the decrease of crystallinity degree. It is proved that solar radiation has no obvious effect on the properties of composites. The flexibility, ILSS and dielectric properties has little change. The tensile strength is slightly improved, and the compression strength is slightly decreased. A decrease of 11.8% is obse-rved on K49/5224A composites and 6.6% for that of F-Ⅲ/5224A. It is because of that the degrad-ation occurred on the surface of composites.
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