Influence of reinforcing continuous carbon fibers on the viscoelastic properties of the epoxy matrix

Abstract The influence of reinforcing continuous carbon fibers (AS4) on the creep and fracture of the epoxy (3501–6) matrix was studied by dynamic mechanical thermal analysis test, creep test and constant strain rate test. While the glass transition temperature (T_g) of the epoxy matrix (512 K) was increased by 5–6°K by the reinforcing fibers, the activation energy for creep/relaxation was the same for both the epoxy and its composites except off‐axis composites, for which the activation energy was higher. An increase in the instantaneous and rubbery moduli and a reduction in tanδ_max indicate that the reinforcing fibers stiffen the matrix and reduce the extent of viscous deformation in the epoxy matrix. This is corroborated by the creep results that recorded a reduction in the creep rate and the magnitude of creep of the pure epoxy due to the reinforcing fibers. A consequence of this reduction in energy dissipation by viscous deformation, in the epoxy matrix due to the reinforcing fibers, is a decrease in the toughness (i.e. the total fracture energy) of the epoxy matrix measured by constant strain rate test.