Radiation effects on composites for long-duration lunar habitats

Fiber-reinforced composites are of great interest to NASA for deep-space habitation missions due to the specific strength, modulus and potential radiation shielding properties. However, the durability of these materials on long-duration missions has not been evaluated. Few studies have been conducted on the radiation effects of fiber-reinforced composites in space and even fewer have been conducted with high-energy protons, which replicate portions of the deep-space radiation environment. Furthermore, previous studies of carbon fiber-reinforced composites focused on pure epoxy composites, and aerospace composites in use today include toughening agents to increase the toughness of the material. These toughening agents are typically either rubber particles or thermoplastics, known to be susceptible to ionizing radiation, and could affect the overall composite durability when exposed to high-energy protons. Thus, NASA has undertaken a study to understand the long-term radiation effects on one such potential composite for use in deep-space habitats (boron fiber, carbon fiber and semi-toughened epoxy). Samples were irradiated with 200 MeV protons in air to different doses and evaluated via tensile tests, differential scanning calorimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The results showed evidence of a weakened matrix due to scission effects and interfacial failure as a result of resin debonding from the boron fibers.