Researchers from the German Aerospace Center (DLR) in Stuttgart have developed a repair process for fiber-reinforced polymers (FRP). The process follows a “sticking plaster” approach and according to the researchers, is more cost-effective and resource-efficient than traditional methods.

The DLR scientists want to stop prematurely disposing of FRP components and reduce waste during production.

“As the production of FRP components is complex, and therefore costly, repair processes have generally been time-intensive, inflexible and expensive,” says project leader, Markus Kaden from the DLR Institute of Structures and Design. “Large structures – such as those in an aircraft fuselage – are designed for a service life of up to 30 years. In the event of damage, they usually have to be removed for repair or completely replaced."

Components made of fiber-reinforced polymers involve a more complicated repair process as opposed to metal structures, where the damaged area is cut out and new metal riveted in.

"As the fibres are load-bearing and are responsible for the cohesion and resilience of the structure, we cannot simply drill and rivet here; that would only damage the fibers even more," says Kaden.

With the new process, the DLR researchers take away the damaged layers of the material and replace them with a patch similar to a sticking plaster. The patch is made of the same material, has the same fiber alignment and is bonded to the surrounding structure using heat and pressure.

As a first step, the researchers removed the damaged material using a laser. Kaden says that unlike other methods, in which the material is removed with a milling cutter, his team's process rerquires no cooling, there are no clamping or pressure forces on the structure and the tool wear is limited.

In a second step, researchers heat the area of the patch and the damaged area of the structure only. They do this using a metal sheet heated by induction that is the same size as the patch and is pressed onto the patch by creating a vacuum. The patch is then bonded with the surrounding structure under pressure and at a high temperature.

The researchers have also developed a mobile repair station that can be used to demonstrate the process, and uses the systems required for repairing FRP structures.