Influence of oxidative environments on damage in c/epoxy laminates subjected to thermal cycling

The aim of this study is to characterise damage processes in carbon/epoxy laminates submitted to thermal cycling in neutral (nitrogen) and oxidative (air, oxygen) atmospheres. Observations of the polished edges of the specimens by optical microscopy and SEM have revealed the presence of matrix shrinkage and fibre/matrix debondings only on samples tested under oxidative atmospheres. Quantitative analyses of transverse matrix cracking by means of microscopy and X radiography have shown the accelerating effect of an oxidative atmosphere. Moreover, the higher the oxygen concentration, the more significant the acceleration of the cracking development. These results are analysed in terms of matrix oxidation, occurring at the highest temperatures of the cycle, and fatigue matrix cracking, occurring at the lowest ones and due to the prevented differential expansions of the plies. During a thermal cycling test performed in an oxidative atmosphere, a coupling effect between these two damage mechanisms would result in the acceleration of the micro cracking observed.