Thermal aging of fiberglass/carbon-fiber hybrid composites

Thermal oxidation of a unidirectional carbon-fiber/glass-fiber hybrid composite was investigated to determine oxidation kinetics and degradation mechanisms. The epoxy composite rods were comprised of a carbon-fiber core and a glass-fiber shell. A reaction–diffusion model was developed for each of the two hybrid sections to obtain the oxygen-concentration profile and the thickness of the oxidized layer (TOL) within the composite rods. The TOL was measured experimentally for samples exposed at 180 °C and 200 °C for up to 8736 h, and measured values were similar to the modeling predictions. The glass-fiber shell functioned as a protective layer, limiting the oxidation of carbon-fiber core. A relationship was derived relating TOL to tensile strength of the hybrid composite. The tensile strength remained essentially unchanged by thermal oxidation after 52 weeks of exposure. Inspection of thermally aged capped rods showed no cracking after long-term exposures.