Preliminary work studied the best way to integrate nanoparticles – specifically carbon nanotubes (CNT) at the joined interface. To this end, 3 types of ‘interleaving’ methods, where a film is embedded in the midplane of composite layup, were investigated. The results from this investigation were presented virtually at the American Society of Composites conference[2].
Once the best approach to embed the interleaf was established, two main parameters that could affect the nature of damage propagation and fracture toughness in the co-cured interface were explored: the concentration of CNT and thickness of the interleaf. Coupons containing different combinations of CNT concentrations and interleaf thicknesses at the co-cured interface were manufactured and tested under different loading conditions. The results from mode I – a peeling type load that causes crack growth, were presented at the 20th European Conference on Composite Materials in Lausanne [3]. The extended investigation containing microscopic analysis of the failed interface in mode I as well as the results from mode II (a sliding type load at the interface) and mixed I/II modes are being prepared for 2 peer-reviewed journal publications: one targeted for Composites Science & Technology and another for Journal of Composite Science. Test results revealed that inclusion of CNT had a significant effect in delaying damage by arresting the growth of cracks as well as improving fracture resistance of the interface. Mode I tests also exhibited a dramatic shift in the nature of crack growth and imaging at the nanoscale showed CNT directly interacting with the crack and creating crack diffusion. In mode II, the CNT interleaved samples showed up to 4 times enhancement in fracture resistance. These findings encouraged us to attempt a scale up of the approach into a T-joint where the critical damage-prone regions are the interface between the skin and web and the delta fillet (central triangular region).
The design, manufacturing, and testing of T-joints containing CNT in the interface as an interleaf and in the delta fillet as a paste was successfully realized. The T-joints containing CNT interleaves at the skin-web interface showed higher failure initiation load and stable crack propagation followed by delayed final failure displacement. The overall fracture energy required to fail the T-joint was more than double the baseline T-joint containing no CNT.
The execution of this project has opened up several opportunities for me to deliver invited talks [4,5] at universities, carry out supervision and mentorship of a Master’s student [6], and foster networking in the DEWIS (Delft Women in Sciences) group [7]. An idea that spurred from this project was submitted as a proposal to NWO (Dutch Science Council) Veni and invited up to the final round of evaluations.
2. N. Subramanian, C. Bisagni, “Multiscale damage in co-cured composites – perspectives from experiments and modelling”, Proceedings of the American Society for Composites- 36th Technical Conference - 2021.
3. N. Subramanian, C. Bisagni, “Damage arrest mechanisms in nanoparticle interleaved composite interfaces”, Proceedings of the 20th European Conference on Composite Materials 2022. ISBN: 978-2-9701614-0-0
4. N. Subramanian, “From bench to flight: the role of engineered materials in aerospace”, Invited Seminar at Amrita School of Engineering, India, September 2021.
5. N. Subramanian, “Role of novel materials in future aviation”, Invited Lecture, Xidian University School of Aerospace Science and Technology, China, January 2022.
6. D. Qiao, “Manufacturing and Mechanical Testing of Composite T-joints with Carbon Nanotube Interleaves”, Master Thesis, Faculty of Aerospace Engineering, Delft University of Technology
7. “An interview with postdoc Nithya Subramanian”, DEWIS Interviews:
https://www.tudelft.nl/over-tu-delft/strategie/diversiteit-en-inclusie/netwerk-partners/dewis/news/interviews/an-interview-with-postdoc-nithya-subramanian(öffnet in neuem Fenster)
