Long-Term Environmental Durability of F/A-18 Composite Material

The long-term environmental durability of AS43501-6 graphiteepoxy composite was evaluated by a ground exposure trial conducted at four locations within Australia and one in Malaysia for a period of between 468 and 520 weeks. The combined effects of moisture uptake, UV degradation, temperature, rainfall and wind on the strength of the samples were all evaluated. The coupons absorbed an average of about 0.9 moisture by weight over the length of the trial. The residual strength of the coupons was determined using the interlaminar shear strength ILSS test ASTM D2344 both at ambient temperature and 100 deg C. A statistical analysis of the results determined that the combined effect of moisture and elevated temperature 100 deg C decreases ILSS by about 10. A small enhancement in ILSS at room temperature was noted for specimens which absorbed moisture over the period of the trial. This is likely to be due to the combined effects of stress relief and plasticisation of the matrix. No other significant degradation mechanism was identified in this study apart from a slight decrease in ILSS of about 5 for specimens which were coated with the standard FA-18 paint scheme. This may be attributed to the solvents used in the application of the paint However, the benefits of the paint protecting the composite surface from erosion and UV degradation far outweigh this structurally insignificant change in ILSS.