Periodic Reporting for period 1 - MACADAMIA (Machine learning Augmented Computational Analysis of composite panels: new insights into DAmage Mechanisms In Aerospace structures with nanoparticles)
Reporting period: 2020-09-01 to 2022-08-31
The motivation of this project is to enable the design of primary aircraft components with fewer parts and lower weight by joining composite panels without mechanical fasteners. Such lightweight stiffened panels are critical to mitigating aviation’s environmental footprint, currently at 3.5% due to emissions and land-use effects [1], and aligning with Europe’s goal of carbon-neutral aviation by 2050. However, mechanical fasteners are used in large quantities when bonded and/or co-cured composite joints are employed in primary load-bearing structures i.e. fuselage and wings. This conservative design is warranted because a reliable prediction of damage propagation and failure in composite joint panels is unavailable with current strategies, leading to their consequent ‘overdesign’ and added structural weight.
To accomplish the objective of designing joints with high damage tolerance without the use of fasteners, MACADAMIA focuses on joining composites via co-curing in the presence of nanoparticles at the interface. The project objectives involve testing the effectiveness of using nanoparticles at the interfaces to arrest/delay crack growth and to understand the multiscale nature of crack propagation at joined interfaces.
A proof-of-principle approach of integrating nanoparticles in co-cured interfaces is demonstrated and the interfacial fracture properties are measured under different loading modes. A new manufacturing approach to include nanoparticles as partially-cured interleaves is realized. A change in the nature of damage propagation is observed due to the direct interaction of nanoparticles with the crack front. Furthermore, the same approach is scaled up to a T-joint (highly common aircraft joint) where the nanoparticles are embedded in critical damage-prone interfaces and revealed to improve the resistance and stability of crack growth in the structure. Thus, this technique may open avenues to manufacture reliable aircraft components with fewer mechanical fasteners.
1.Lee David S., et al. Atmospheric Environment 244 (2021): 117834.
To accomplish the objective of designing joints with high damage tolerance without the use of fasteners, MACADAMIA focuses on joining composites via co-curing in the presence of nanoparticles at the interface. The project objectives involve testing the effectiveness of using nanoparticles at the interfaces to arrest/delay crack growth and to understand the multiscale nature of crack propagation at joined interfaces.
A proof-of-principle approach of integrating nanoparticles in co-cured interfaces is demonstrated and the interfacial fracture properties are measured under different loading modes. A new manufacturing approach to include nanoparticles as partially-cured interleaves is realized. A change in the nature of damage propagation is observed due to the direct interaction of nanoparticles with the crack front. Furthermore, the same approach is scaled up to a T-joint (highly common aircraft joint) where the nanoparticles are embedded in critical damage-prone interfaces and revealed to improve the resistance and stability of crack growth in the structure. Thus, this technique may open avenues to manufacture reliable aircraft components with fewer mechanical fasteners.
1.Lee David S., et al. Atmospheric Environment 244 (2021): 117834.
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
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
One of the most relevant outcomes is the demonstration of damage resistant interfaces when composite parts are joined without mechanical fasteners. The approach developed in this action is also easily integrable with existing manufacturing techniques. The dispersion of CNT in a host polymer and the generation of filmed interleaf does not require advanced tooling or equipment other than thermal ovens. The process is compatible with standard composite layup steps and autoclave curing. Therefore, the improvement of fracture toughness in critical composite interfaces can be realized with this new approach when integrated into already existing manufacturing approaches. This work has not only generated new insights into the altered damage mechanisms at interfaces upon the introduction of CNT but may also open up avenues for applied research in controlled morphology of CNT integration and optimized co-cured interfaces.
The wider anticipated impact of this study is the certification of primary aircraft parts with optimized interfaces that are cleared for use without mechanical fastening. Such designs would yield a major reduction in the structural weight and associated fuel use, much in alignment with the EU Destination 2050 report, which lays out that innovations to reduce aircraft fuel burn (such as weight reduction) can lead up to 50% lower greenhouse gas emissions.
The wider anticipated impact of this study is the certification of primary aircraft parts with optimized interfaces that are cleared for use without mechanical fastening. Such designs would yield a major reduction in the structural weight and associated fuel use, much in alignment with the EU Destination 2050 report, which lays out that innovations to reduce aircraft fuel burn (such as weight reduction) can lead up to 50% lower greenhouse gas emissions.