• Researchers from IMDEA Materials Institute and AIMEN Technology Centre are behind the development of printable sensors which offer strain monitoring and damage detection of airframe components.
• The breakthrough could lead to both novel airframe manufacturing routes and safer aircraft.

IMDEA Materials researchers have led a groundbreaking study into the development of novel carbon nanotube (CNT) yarn-based strain sensors for the structural health monitoring (SMH) of airframe components.

SHM provides a critical assessment of component in-service performance and integrity and is a key measure to improve the safety and reliability of modern aircraft. 

The study, Strain sensing of structural composites by integrated piezoresistive CNT yarn sensorsis the collaborative work of researchers from IMDEA Materials and Galicia’s AIMEN Technology Centre.

It outlines the development of the sensors, which offer piezoresistive sensing of thermoplastic airframe parts. Current SHM systems, such as strain gauges, acoustic and vibration sensors, and fibre optic sensors, remain problematic due to limited measurement range and, in some cases, expensive hardware and difficulties in handling. 

The innovative approach taken by the researchers, as part of the European Union’s Horizon 2020 research project DOMMINIO, involves integrating CNT yarns into structural thermoplastic carbon fiber-reinforced polymer (CFRP) laminates.

The flexible and robust CNT yarn-based sensors are designed to be fully integrated in an airframe component at manufacturing, thus avoiding bonding and delamination problems. They are seen as a key component of future integrated SHM-systems with real time data-driven fault detection.

Focused on the development of sensors based on polyetherketoneketone (PEKK) coated thermoplastic filaments reinforced with continuous CNT yarns, the paper outlines the strain sensing capabilities in comparison with commercial strain gauges.

“We’ve reached a significant milestone in manufacturing the lab-scale panels with fully integrated CNT sensors using the high-performance polymer of a PEEK-family,” explained Dr. Anastasiia Mikhalchan, one of the corresponding authors.

“Lightweight structural composites based on thermoplastics occupy a significant market share in aerospace nowadays, so it is important to showcase the relevance of CNT-yarn based materials to this trend,” she added.  

The sensors were able to detect the tensile and compressive deformations in different bending loadings with a gauge factor in the order of 12 for tensile deformations up to 0.2% strain.

Effectively, this means they are able to detect potential problems in the structural integrity of components earlier, and with greater accuracy, improving aircraft safety and maintenance.

“The paper demonstrates the encouraging strain-sensing capabilities of CNT yarn-based sensors, integrated in CFRP laminates by hot press consolidation,” stated Dr. Mikhalchan.

“The research has significant implications for the future CNT yarns commercialisation in the aerospace industry, targeting lightweight airframes, sustainable materials and multifunctional performance.”

“One of the key findings of the DOMMINIO project is that CNT fibres and yarns are compatible with demanding polymer matrixes, Fused Filament Fabrication, and robotised technologies, such as Automated Fibre Placement (AFP).”

“The results open the door for complex geometries and innovative designs of airframe components.”

Along with Dr. Mikhalchan, the researchers behind the study include IMDEA Materials’ Prof. Carlos González, Drs. Juan José Vilatela and Davide Mocerino, and Moisés Zarzoso, and Drs. Pablo Romero and Ricardo Losada from AIMEN.

The results were highlighted in the special issue, Advanced High Strength Composites for Aerospace Structures of Composites Part B: Engineering, one of the leading scientific journals in the composites field.

The special edition showcases the leading work over the past 5 years in the field of novel high-performance CNT-based materials and their applications in aerospace sector.

It was led by Guest Editors, Prof. Gregory Odegard, Director of NASA Space Technology Research Institute for Ultra-Strong Composites by Computational Design, Prof. Zhiyong Liang (Florida State University), Prof. Ibrahim Guven, (Virginia Commonwealth University) and Dr. Emilie Siochi, Senior Researcher at NASA Langley Research Centre.

Dr. Mikhalchan admitted that an invitation to participate in the prestigious special issue had come as something of a surprise.

“To be honest, I was shocked to see my name in the invitation list,” she said. “The fact that this special issue is organised by NASA and such leading experts in the field speaks for itself.”

“The opportunity to contribute and show up our latest applied research on CNT-based materials is an honour for me, and for all of the co-authors involved”.

This work was supported by the funding from the European Union’s Horizon 2020 research and innovation programme under the Grant agreement No 101007022 (DOMMINIO).