Patched repair paves the way for onsite repair of composite structures

In October 2019, DCMC partners have successfully performed a demonstration patch repair on a composite panel. The planned repair was a milestone in DCMC’s innovation track Field & Onsite Repair of Composite Structures. This project is sponsored by the Dutch Ministry of Defence and designed to develop an onsite solution for automated structural repair of composite structures with long-term quality assurance.

The exponential growth in the use of composite materials in aviation is leading to problems with regard to the repair of these materials. Where composites techniques are being perfected, little is known about the quality and durability of repairs of composite materials. Only a scarce number of specialised technicians can perform these repairs, but the materials cannot always be moved to where the defective aircraft is located.

Repair patch
As part of this innovation track DCMC partners developed a repair method that can be automated and applied at location. This method was tested on a demonstration repair panel manufactured by KLM. First, the TU Delft and TiaT measured the geometry of the panel and inspected the damaged area using Ultrasound and Thermography. From these measurements a data file was created that was used by GKN-Fokker to manufacture the repair patch. A mobile milling machine was used to cut a circular area out of the repair panel around the damaged area.

A film adhesive was cut to shape and placed onto the panel cut-out and patch. Final bonding of the patch was done by GKN-Fokker and SPECTO using a heated blanket and vacuum bagging to cover the repair area. A hot bonder composite repair system was used to control the vacuum and curing temperature. The bottom side of the panel was covered by a foil to prevent vacuum leakage and adhesive outflow. After curing for two hours at 120 °C the blanket and bagging was removed. As the last step, excessive adhesive was removed from the repaired area.

Microscopic inspection
The next step will be Non-Destructive Inspection (NDI) by TU Delft and microscopic inspection of the bonding interface by Royal NLR. The data generated by this demonstration repair will be used to further investigate automation of the entire repair chain from automated inspection to automated milling and application of the repair patch. Algorithms will be developed to combine NDI inspection data and geometry of the damaged area in order to create a milling file for automated preparation.

Click here for more information about the innovation track Field & Onsite Repair of Composite Structures.