small Scale interlocking mechanisms for Strong and Tough mEtamatEriaL

Project Information

SSTEEL

Grant agreement ID: 948336

DOI

10.3030/948336

EC signature date 4 September 2020

Start date 1 March 2021

End date 30 September 2027

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 711,00

EU contribution

€ 1 499 711,00

Coordinated by

IMPERIAL COLLEGE OF SCIENCE TECHNOLOGY AND MEDICINE
United Kingdom

Periodic Reporting for period 3 - SSTEEL (small Scale interlocking mechanisms for Strong and Tough mEtamatEriaL)

Reporting period: 2024-03-01 to 2025-08-31

Summary of the context and overall objectives of the project

Brittleness limits the design and lifetime of some polymeric, metallic, and almost all ceramic materials in both structural and functional engineering applications, from the design of plane engine turbine blades to the newest solid-state electrolyte in batteries. This brittleness is intrinsically present in material composition that cannot plastically deform and make them sensitive to any defect introduced during their fabrication or usage. This issue becomes societal when we consider that the brittleness of a material will influence its durability and lifetime. Taking a brittle material that is needed for any other of its properties and toughening it will lead to more durable solution to structural and functional applications.
The goal of this project is to produce small Scale interlocking mechanism for Strong and Tough mEtamatEriaL (SSTEEL) that will provide a material independent solution to brittleness. Interlocking mechanisms provide in theory one of the most efficient ways to increase toughness by creating crack blocking compressive stresses in response to tensile stresses. Because a brittle material strength is inversely linked to its size, Objective 1 will be used to develop a new process to form interlocking mechanism based on micron-sized elements using a combination of light-based additive manufacturing, shrinking ink design to access sub-printer resolution, and fragmentation. Objective 2 will be to implement this mechanism at an even smaller scale using rational material selection, solid state chemistry, and colloidal processing to fabricate an interfacial binder for the elements. The fracture process of SSTEEL sample will span several length scales and a specific task will be to use a combination of image correlation and modelling to fully characterise the existing damaging mechanism and inform the improvement of future designs.
These new structures and concepts developed by my group will promote the development of tough structure for today’s and future structural and functional engineering applications by changing any brittle material to become strong, stiff, deformable, and reliable materials.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Objective 1 was to design a new process based on Digital Light Printing to control the formation of interlocking mechanisms. Interlocking mechanisms are based on controlled local change in the thickness of reinforcing elements in a composite, which could be platelets, fibres or any other arbitrary shapes. In Digital Light Printing, the amount of light received by the ink can be accurately controlled and will change the local thickness of the solidified ink. The built-in printer software are not made to control the light pattern in that way. Challenge 1.1 was thus set up to create our own program to generate the input for the printer. This task is now complete, and we could control the local thickness of the printed down to the 5-10 µm scale in thickness and the native lateral resolution of 27 µm. This will allow us to study the presence and potency of the interlocking mechanisms in details to find material-independent guidelines. During challenge 1.2 we will work on ceramisation of polymers to reach even higher spatial control and perform the fracture testings.
Objective 2 was to design interlocking mechanisms at the nanometric scale by providing a strain hardening ceramic binder between ceramic reinforcing elements. This objective is already a success, with promising results and Intellectual Properties generated. We managed to get a fully ceramic composites that show significant plastic deformation in tension at high temperature. We are currently investigating the mechanisms responsible but thanks to our initial insights we have already several candidates of other binders that display this unusual behaviour.
Objective 3 is to focus on understanding the fracture of complex composites using in situ optical characterizations. This objective is also making significant headway as we managed to custom-build an in situ optical setup based on large sensor camera and dedicated optics. The fracture of complex materials is difficult to track, as the cracks themselves are within the micron size range, but the damages can be spread out over several millimeters. It was thus a priority to be able to monitor such damages, and our custom-made setup proved up to the task. This setup enabled us to understand better the fracture of complex bioinspired ceramic and to produced better informed finite element models of their fracture. It is currently being upgraded to follow and model damages for materials at temperature up to 2000°C.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Both Objective 1 and 2 are producing already results that are beyond the state of the art in their respective fields. The fabrication of layered composite with a control of the local thickness at the 5 microns scale will allow us to finally test the effect of interlocking on the fracture properties of brittle materials. The flexibility of the method is so large that we are now thinking about using machine learning algorithms informs by Finite Element Modelling calculations to explore numerically the design space and save time on the optimisation of the tough metamaterials. In parallel, we are now looking at producing grain-based materials with corrugated interfaces, a microstructure that is supposed to give flexibility and toughness to rigid materials. This research is directly originating from the questions we asked ourselves on the design of the tough metamaterials in Objective 1.
Objective 2 is yielding already new results, opening possibility for toughening and new fabrication techniques for ceramics composites. That is why the IP generated is currently considered for protection. Based on this newfound knowledge, we already have several candidates to broaden further the conditions for obtaining deformable ceramics by the end of the project.
Objective 3 is also opening exciting possibilities for the characterisation of new composites. The results we obtained with the custom-made setup led us to understand better the fracture of today’s bioinspired ceramics which is now opening new research avenues. We are currently looking into a new type of microstructure thanks to these results, in which we are unveiling the critical role of order and regularity in synthetic composites microstructure on their fracture behaviour for the first time.

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