Spatially resolved, in situ elastic modulus of thermoset polymer amidst carbon fibers in a polymer matrix composite

The mechanical properties of thermoset resins used in carbon fiber composites depend on their processing conditions. The inclusion of fibers into the resin locally affects the thermal balance, creates chemical inhomogeneities, and templates structural developments in the polymer near the fiber surface. In this study we use Raman and Brillouin light scattering to investigate the effect of carbon fibers on the mechanical properties of an epoxy matrix. Our results show that the longitudinal modulus of epoxy within a fiber tow is about 3.75% lower than the modulus of the epoxy outside of the tow. Furthermore, within a fiber tow, the modulus depends on the local packing density of the carbon fibers. Comparison between our Brillouin and Raman measurements suggest that the observed spatial inhomogeneity in elastic properties of the matrix is not a result of residual stresses within the matrix but more likely due to structural reorganization in the interfacial region.