In-situ strain analysis of potential habitat composites exposed to a simulated long-term lunar radiation exposure

NASA is studying the effects of long-term space radiation on potential multifunctional composite materials for habitats to better determine their characteristics in harsh space environments. Two epoxy-matrix composite materials were selected for the study and were mounted in a test stand that simulated the biaxial stresses of a pressure vessel wall. The samples in the test stand were exposed to radiation at fast (0.1478 krad/s) and slow (0.0139 krad/s) dose rates, and the strain and temperature were recorded during the exposure. During a fast dose rate exposure, negative strain was recorded, decreasing with time, an indication of matrix shrinkage. Given previous radiation studies of polymers, this is expected to be a result of radiation-induced crosslinking in the epoxy matrix. However, with a slow dose rate, the materials exhibited a positive strain that increased with time, corresponding to stretching of the materials. This result is consistent with scission or degradation of the matrix occurring, possibly due to oxidative degradation.