EFFECT OF IONIZING-RADIATION ON THE DYNAMIC MECHANICAL-PROPERTIES OF AN EPOXY AND A GRAPHITE FIBER EPOXY COMPOSITE

TGDDM/DDS epoxy and T300/NARMCO 5208 composite specimens were exposed to 0.5 mev electrons to dose levels up to 10,000 Mrad, and the effects of radiation on the mechanical properties were characterized using dynamic analysis (DMA). In nominally cured specimens, there remain unreacted epoxide groups because the epoxy system vitrifies during the cure, preventing additional reaction. DMA shows that ionizing radiation continues the reactions of epoxide groups. Also, the ultimate glass transition is shown to decrease monotonically with radiation dose. The room temperature elastic modulus of the epoxy increases slightly with radiation, but at temperatures exceeding 100°C, there is a slight decrease with radiation. There is a dynamic loss phenomena associated with the composites, not seen in the epoxy, that is thought to be due to the interphase region between the fiber and the matrix.