In a study of T300/934 graphite/epoxy composite, which forms the composite skin of the space shuttle cargo bay doors, the following composite properties were investigated as a function of increasing gamma-radiation exposure dosages: directional moisture absorption/desorption kinetics, glass transition temperatures, interlaminar shear strength and damping peaks (tan δ). Irradiation conditions were: open to atmosphere and vacuum, ambient and high temperature (100°C).

Four dosage levels were investigated: 4 × 10⁷, 8 × 10⁷, 1.4 × 10⁸, and 3.2 × 10⁸ rads, the final dosage level being equivalent to a three-year orbit life. Directional moisture diffusion studies indicate anomalies in the three diffusing axes (translaminar, transfibrous, and interlaminar). Interlaminar shear strengths showed an initial increase, followed by a decrease, as the dosages increased. Although the glass transition temperatures remained essentially unchanged, the peak heights of the tan δ measurements also showed an initial increase, and then decreased as radiation dosages increased.