Surface Treatments and Adhesives for Bonded Repairs to High Temperature Carbon–Bismaleimide Composite Structure

Abstract

Modern aircraft utilises composite structures in an increasing number of applications, including higher temperature regions to gain the benefit offered by the high stiffness and strength of composites at lower equivalent weight compared to metals. The higher temperature structure poses unique problems for onaircraft bonded repair. Often in situ bonded repair temperatures may be limited due to the ability to heat the structure to high temperatures, caused by sub-structure acting as heat-sinks or concerns that material properties of the airframe could be compromised. Consequently, the repair adhesive needs to restore the composite laminate structure strength without the benefit of cure temperatures employed in the original construction. This paper examines suitable adhesives for high temperature bonded repair applications to composite laminate and reliable surface treatment methods for the composite laminate structure prior to bonding. Results indicate that thermal characterisation of the adhesive can provide a reliable screening method for adhesive selection and both plasma and laser treatments of the composite may increase reliability of the bonded repair strength compared to more common treatments. FM32 oxy-amide adhesive was found to be the best candidate repair adhesive examined.