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On board for aircraft repairs

5 Mar 2019

A process that improves repair of carbon fiber airplane components may benefit Singapore’s avionic industry

A team from A*STAR is helping Singapore companies that specialize in the maintenance, repair, and overhaul of airplanes to deepen their understanding of a technology for repairing high-tech carbon fiber components.

Carbon fiber structures are strong enough to replace avionic parts typically made from steel. But when damaged, these lightweight materials require special repair techniques to ensure they can still bear mechanical loads. Technicians normally cut wedge-shaped chunks from the defective site, and glue in pre-made patches. Finally, components are placed in pressurized ovens called autoclaves to remove volatile gases and cure the adhesives.

Autoclave-based repair techniques, however, are impractical for maintenance of extra-large components, such as wings or fuselages, that cannot be removed from the aircraft. Stefanie Feih and co-workers from A*STAR’s Singapore Institute of Manufacturing Technology (SIMTech) have now investigated a technique for patching carbon fiber structures while they are still in place on the aircraft.

The team studied a double vacuum debulking process that places a rigid box containing an inner flexible vacuum bag on top of a patch. By creating a second and different vacuum level within this chamber, volatile gases can be quickly removed from the repair material. The patch is then transferred to the aircraft to complete the curing step.

“Double vacuum debulking adds an additional step to an already very complex repair scenario,” says Feih. “Repair processes require highly accurate surface temperature control over surfaces with generally complex internal features. Performing large scale repairs further complicates the process.”

High porosity in the final patch is a significant issue during carbon fiber repair, because voids can lessen mechanical strength. The researchers found that the adhesive films used to bond repair patches can also trap volatile gases to create additional voids. The double vacuum debulking process, however, was found to almost completely eliminate porosity in both the adhesive film and repair patch for all repair geometries.

“These findings highlight why you need a highly skilled workforce in an avionic hub city,” says Feih. “It’s crucial for attracting operators to Singapore, and we undertook this project to improve the understanding of repair processes for composite structures among local companies.”

Feih and colleagues also examined the impact of patch geometry by mechanically testing configurations ranging from simple laminate films to more complex wedge shapes. Here, circular 3D repairs proved inherently stronger than simplified 2D shapes when under tension.  Further study is needed to determine optimal improvements under complex conditions experienced by real components during flight.

The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology (SIMTech).  For more information about the team’s research, please visit the Polymer Joining webpage.

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Chong, H. M., Liu, S. L., Subramanian, A. S., Ng, S. P., Tay, S. W. et al. Out-of-autoclave scarf repair of interlayer toughened carbon fibre composites using double vacuum debulking of patch. Composites: Part A 107, 224–234 (2018). | article

About the Researcher

Stefanie Feih

Senior Scientist II

Singapore Institute of Manufacturing Technology
Dr Feih is a Senior Scientist II in the Joining Technology Group at SIMTech in Singapore. She has over 20 years of international research experience. Prior to joining SIMTech in 2014, Dr Feih was a Senior Lecturer in the School of Aerospace, Mechanical and Manufacturing Engineering at RMIT University in Melbourne. Dr Feih previously worked as a post-doctoral researcher at Riso National Laboratory (Denmark). Dr Feih is an Executive Council Member of the International Committee on Composite Materials (ICCM). She holds an Adjunct Associate Research Professorship at the National University of Singapore and an Adjunct Professorship at RMIT University, Australia.

This article was made for A*STAR Research by Nature Research Custom Media, part of Springer Nature