A new handheld device has been created to fix almost invisible damage on materials made from carbon fiber and epoxy. The researchers tested this device on materials with different numbers of layers, 16 and 24, and tried three types of adhesives: regular epoxy, epoxy mixed with special particles called halloysite nanotubes (E1HNT), and epoxy mixed with carbon nanotubes (NF100, also known as 'NanoForce E100' from Nano-Tech SPA https://www.italnanotech.com). They used infrared technology and compression testing to see how well the repairs worked.
Unfortunately, all the damaged materials were much weaker than undamaged ones. The researchers found that the number of layers in the material was the most important factor affecting how well the repair worked. For the 16-layer material, using regular epoxy or E1HNT in a vacuum worked best for restoring its stretchy properties, while using E1HNT adhesive at regular atmospheric pressure worked best for fixing its fractures.
However, for the 24-layer material, the repairs didn't fully bring back its original strength because the damage was more complicated. The researchers discussed which repair methods were most effective for restoring certain properties of the materials.
Prior to this study, the researchers had studied the properties of different types of resin to find out which ones would work best for repairing damaged composite materials . They considered the halloysite nanotubes (HNT) and carbon nanotubes (CNT) that can be mixed into adhesives to make them better for fixing the damaged materials. However, they needed to check how well these particle-adhesive blends performed, considering factors like how they were prepared, the effects of the types of particles used, and how much of them were added.
They studied two commercially available adhesives, Epo-Tek 301 and NanoForce E100 (i.e. from Nano-Tech SPA), and also prepared mixtures of Epo-Tek 301 with different amounts of HNTs, and Epo-Tek 301 with treated and untreated CNTs. They examined various properties of these adhesives, including how strong they were (using a dedicated micromechanical tester developed jointly by researchers from Sensorcraft Technology (S) Pte Ltd (https://sensorcraft.com.sg) and Newcastle University in Singapore), how well they stuck to things, their physical traits like how they spread out, their ability to handle heat, and their chemical characteristics.
The results showed that adding 1% of HNTs to Epo-Tek 301 didn't change its properties much, but using more HNTs made the adhesive weaker and changed its behavior when exposed to heat. On the other hand, adding CNTs didn't make the adhesive any better in terms of its properties. In fact, the adhesives with CNTs became thicker and might not work well for repairing composite materials since they might not seep into the damaged areas easily.
So, when choosing an adhesive to repair damaged composite materials, it's important to choose wisely considering all these factors.
Importantly, both studies were the results of strong sustained support from industry partners, namely Nano-Tech SPA (which supplied the adhesives) and Sensorcraft Technology (S) Pte Ltd (which provided the micromechanical tester). The results have also benefited these companies, providing new and important areas of applications, namely Maintenance, Repair and Operations (MRO), for their products.
The team comprised researchers from Newcastle University in Singapore, namely Dr Wei Liang Lai, Associate Professor Kheng Lim Goh, Associate Professor Eugene Wong (now at Singapore Institute of Technology), from Newcastle University UK, Professor Geoff Gibson (who passed away in 2021), and Republic Polytechnic, namely Dr Hamid Saeedipour. The lead researcher, Dr Wei Liang Lai, did this project as part of his PhD study, under the supervision of Associate Professor Kheng Lim Goh. Dr Wei Liang Lai is now a lecturer at Republic Polytechnic. This project was funded by Singapore Ministry of Education, Grant/Award Number: MOE2013-TIF- 1-G-068. This project has also won the team the Institution of Engineers, Singapore, Prestigious Engineering Achievement Awards 2021. The award was conferred specifically for 'Innovative evaluation and repair of thermal defects in aircraft composite structures'.
For more information the reader can refer to the published papers, including earlier preliminary study papers [3-8], or contact Dr Wei Liang Lai at [email protected], or Associate Professor Kheng Lim Goh at [email protected]
 W. L. Lai, H. Saeedipour, W. L. E. Wong, and K. L. Goh, "In situ resin-injection approach for repairing barely visible impact damaged carbon-fiber reinforced epoxy laminates: Optimizing the repair parameters using Taguchi method," Polym Compos, vol. 44, no. 6, pp. 3372-3386, 2023, doi: https://doi.org/10.1002/pc.27327.
 W. L. Lai, N. Sachdeva, Y. V. Tan, P. Pasbakhsh, H. Saeedipour, and K. L. Goh, "Experimental assessment on the mechanical, physical, thermal, and chemical properties of halloysite and carbon nanoparticles reinforced epoxy resins for repair applications," Polymers for Advanced Technologies, vol. n/a, no. n/a, 2023/07/11 2023, doi: https://doi.org/10.1002/pat.6150.
 M. A. A.-S. B. Rahman, W. L. Lai, H. Saeedipour, and K. L. Goh, "Cost-effective and efficient resin-injection device for repairing damaged composites," Reinforced Plastics, vol. 63, no. 3, pp. 156-160, 2019, doi: 10.1016/j.repl.2018.11.001.
 W. L. Lai, H. Saeedipour, and K. L. Goh, "Dataset on mechanical properties of damaged fibre composite laminates with drilled vent-holes for resin-injection repair procedure," Data Brief, vol. 24, p. 103912, Jun 2019, doi: 10.1016/j.dib.2019.103912.
 W. L. Lai, H. Saeedipour, and K. L. Goh, "Mechanical properties of low-velocity impact damaged carbon fibre reinforced polymer laminates: Effects of drilling holes for resin-injection repair," Composite Structures, vol. 235, 2020, doi: 10.1016/j.compstruct.2019.111806.
 W. L. Lai, H. Saeedipour, and K. L. Goh, "Experimental assessment of drilling-induced damage in impacted composite laminates for resin-injection repair: Influence of open/blind hole-hole interaction and orientation," Composite Structures, vol. 271, 2021, doi: 10.1016/j.compstruct.2021.114153.
 W. L. Lai, H. Saeedipour, and K. L. Goh, "Dataset on open/blind hole-hole interaction in barely visible impact damaged composite laminates," Data Brief, vol. 34, p. 106607, Feb 2021, doi: 10.1016/j.dib.2020.106607.
 W. L. Lai et al., "A simple portable low-pressure healant-injection device for repairing damaged composite laminates," International Journal of Mechanical Engineering Education, vol. 45, no. 4, pp. 360-375, 2017, doi: 10.1177/0306419017708645.