Accelerated Aging Versus Realistic Aging in Aerospace Composite Materials. V. The Effects of Hot/Wet Aging in a Structural Epoxy Composite

Samples of an aerospace-grade, carbon-fiber epoxy composite (Hexcell 8552/1M7) were subject to long-term (1 year) hot/wet aging and thermal spiking under different humidity levels and temperature conditions related to the in-service conditions seen in military aircraft. Changes to the chemical and physico-chemical structure of the composite were analyzed by a range of experimental techniques including gravimetric analysis, FTIR, and DMA, to compare the effects of the various aging conditions. The results indicated that, while the chemical changes (as seen by FTIR) in this well cured composite appeared to be only significant at the surface, they did appear to have a deeper influence on some of the major physical property changes observed, such as micro-cracking, glass-transition-temperature (T-g) variations, and Tan 8 curves. These physical changes could not be fully explained by standard water-absorption effects alone but could also be influenced by chemical changes similar to those seen at the surface. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 901-910, 2010