Polymer composites as magnet materials: Irradiation effects and degradation mechanism of mechanical properties

E-glass fabric-reinforced epoxy and polyimide composites were irradiated with 60Co γ-rays or 2 MeV electrons at room temperature. Three-point bend tests were then carried out at 77 K and at room temperature for rectangular specimens having their length axis in a 0deg or 45deg orientation with respect to the warp and fill of the reinforcing fabrics. Irrespective of the composite type and the test temperature, the 0deg specimens fail in a flexural mode, while the 45deg specimens fail in a shear or shear/flexural mixed mode. For the 0deg specimens, the dose dependence of the ultimate flexural strength depends not only on the test temperature but also on the matrix resin in the composite. The complicated dose dependence can be explained systematically by the mechanism that the degradation of the composite flexural strength is virtually determined by a change in the matrix ultimate strain due to irradiation. For the 45deg specimens, on the other hand, the dose dependence of the ultimate interlaminar shear strength is dependent only on the test temperature, and is independent of the matrix resin in the composite. This result suggests that the degradation of the composite shear strength is dominated by the radiation damage at the fiber/matrix interface rather than that in the matrix. (orig.)