Impacts of aggressive aviation fluids on physical and chemical properties of aerospace-grade fiber composites

Fiber-reinforced composites (FRCs) are crucial in the aerospace industry because of their lightweight and durable features. However, concerns exist regarding their performance when exposed to aviation fluids. This study examines how five aviation fluids—hydraulic fluid (HF), isopropyl alcohol (Iso P), dry cleaning solvent (DCS), methyl ethyl ketone (MEK), and an oil-water mixture—affect aerospace-grade carbon and glass fiber composites over 15 and 30 days. MEK caused the highest fluid absorption in both composite types, with glass fiber composites being more prone to degradation. Interlaminar shear strength analysis showed that carbon fiber composites retained better resistance to delamination when exposed to aviation fluids, with MEK causing the greatest reduction in interlaminar shear strength (ILSS). Specifically, the ILSS of carbon fiber composites decreases by about 30% in MEK, while that of glass fiber composites drops by around 45%. Dynamic mechanical analysis demonstrated notable decreases in storage modulus and glass transition temperatures, indicating significant softening of the polymer matrix. Energy dispersive spectroscopy identified fluid-specific elemental signatures at fiber-matrix interfaces, such as phosphorus and sulfur enrichment in HF-treated samples and chloride penetration in MEK-exposed specimens. The superior performance of carbon fiber composites results from better interfacial stability compared to hydroxyl-rich glass fiber surfaces, which are vulnerable to chemical attack. This research provides insights for designing more fluid-resistant composites, paving the way for safer and more durable solutions in aerospace engineering.