Effects of moisture ingressions on mechanical properties of honeycomb-structured fiber composites for aerospace applications

Abstract

Composite structures are usually subjected to a wide range of environmental conditions whereby they can absorb a substantial amount of moisture, oil, or solvent from the environment, thus reducing their mechanical, thermal, electrical, and other physical properties and service times. In this study, hydrophobic barrier films used to prevent moisture ingression into sandwich structures are investigated. Four different hydrophobic thin barrier films—polyvinyl fluoride (PVF), polyether ether ketones (12.5 and 25 μm), polyimide, and polytetrafluoroethylene—were co-bonded to the surfaces of fiber composite sandwich structures to study the changes in mechanical properties of the sandwich structures before and after immersing them into deionized (DI) water and aviation hydraulic fluid (Skydrol®). For comparison and evaluation purposes, the composite coupons underwent two different mechanical tests: sandwich flexure and compression strength compression. Test results confirmed that using barrier films as the outermost ply on composite sandwich structures significantly reduced moisture ingression, and as a result, mechanical properties were considerably increased compared to those coupons without any barrier films.