How do I repair my structures?

The topic of repair is involved and requires several areas of expertise related to composites, this includes machining and removal of the damaged zone, surface preparation, including paint removal, repair fabrication and evaluation of the durability of the repair.

There are essentially two methods of structural repair, adhesively bonded repair and bolted repair. The repair may either be a patch on the outer surface or a plug to replace the damage material. Often both a plug and a patch are used. For thicker laminates, a scarfed plug may be used. Similarly, often both a bolted and bonded repair scenario is used. Adhesively bonded repairs are designed so that that the adhesive is loaded as much in shear as possible. Attention must be given to the surface preparation to ensure that the repair is correctly bonded to both the damaged structure and the repair patch.

Some of the issues for the design of a repair include:

Durability: The repair must be considered to give an equal life to that of the original structure and be able to maintain its integrity under fatigue loading and environmental exposure. For adhesively bonded repairs, the adhesive itself must not degrade significantly with time. Any bolted repair must not cause corrosion, especially as dissimilar materials may be used.

Stiffness: For composite structures that have been designed to be of high stiffness and low weight, the repair must allow the original structure to maintain its structural stiffness and strength. Variations in load path created by the repair should be minimised.

Surface Finish: Dependent on the application the surface finish must be considered. This may be, for example, because the surface must retain its aesthetic appearance, aerodynamic capabilities or fluid retention capabilities.