The design of a high performance composite component achieves high strength and light weight by the combination of material layers, fibre orientation and specialist resins.
Repairs to high performance composite components can rebuild the structure, to match the performance of the original part. This requires specialist repair techniques to match the original engineering design of the component.
Local damage, such as cracks, holes or delamination is removed. The repair area is ground back to achieve a shallow scarfe angle (the required joining angle varies according to the material being repaired). The repair area is rebuilt using matching materials and fibre orientation.
Extensive damage may be repaired by rebuilding the shape of the part over a larger area, typically by the use of a partial mould. The mould can be used to support the repair shape, or to prepare repair sections. A moulded composite repair section can be built using matching materials and then scarfe-joined onto the damaged part.
Vacuum may be used to produce denser composite assemblies both for local repairs and larger moulded pieces.
Repairs are put in a temperature controlled curing cycle to ensure that the resin achieves its design strength.
Where required, for example on an aerodynamic surface, the repair area can be finished to a fine surface profile.
Materials commonly used for composite repairs or manufacture include glass reinforced plastic (GRP), carbon fibre and Kevlar.
See: https://en.wikipedia.org/wiki/Composite repairs (for more technical info)