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Hybrid Fibre-reinforced composites: achieving Synergetic effects through microstructural design and advanced simulation tools

Periodic Reporting for period 2 - HyFiSyn (Hybrid Fibre-reinforced composites: achieving Synergetic effects through microstructural design and advanced simulation tools)

Reporting period: 2020-06-01 to 2022-05-31

Fibre-reinforced composites offer excellent specific stiffness and strength and hence can help to reduce fuel consumption and combat climate change. HyFiSyn aims to change the manufacturing-microstructure paradigm to a microstructure-manufacturing paradigm: the manufacturing of composites will be deliberately controlled to yield the targeted microstructure instead of vice versa. This is the only way to maximise the potential benefits of fibre-hybrid composites and composites in general. Since fibre-hybrid composites have a complex microstructure as well as a large design space, this paradigm shift cannot be achieved solely through experimentation. HyFiSyn therefore developed suitable simulation tools to catalyse the desired paradigm shift. These tools will also help in predicting synergetic effects achieved by combining different fibre types. These effects help to maximise the mechanical and functional properties and need to be considered for accurate predictions. The process simulation tools will also help gaining better control of the manufacturing and hence the microstructure. HyFiSyn’s research therefore has 4 objectives:
• To develop simulation tools to predict synergies and to support changes in manufacturing
• To fundamentally understand failure mechanisms of fibre-hybrid composites as a function of their microstructure
• To modify existing manufacturing processes to yield the desired microstructures
• To set up clear guidelines for designing fibre-hybrid composites for specific applications
To achieve HyFiSyn’s ambitious goals, academic partners, material manufacturers and end users jointly tackle these challenges.
HyFiSyn has recently ended, and led to significant progress beyond the state of the art:
- A finite element model was developed to predict stress redistribution around fibre breaks in fibre-hybrid composites, including debonding, thermal stresses and friction.
- A fatigue model for hybrid and non-hybrid composites was developed that predicts the full fatigue life diagram based on realistic micromechanisms.
- A methodology was developed to create digital twins for aligned discontinuous fibre composites based on computed tomography scans.
- A reliable methodology for measuring the strength of UD composites was established.
- Novel thin ply hybrid prepregs and textiles were manufactured and characterised. Excellent dispersion was achieved through a calendaring procedure.
- Functionalities, such as damage sensing, intrinsic reparability, intrinsically heated shape memory behaviour and energy storage, were introduced through fibre-hybridisation.
- We developed processes to (1) optimise pyrolysis processes for recovery of fibre from waste composites and separate out glass fibres from carbon fibres after fibre recovery, and (2) align discontinuous fibres of different types to create novel hybrid microstructures.
We broadly disseminated our results in 10 journal papers (many more in submission and preparation) and many conferences. The tensile testing campaign on unidirectional composites led a round-robin exercise targeting a new ISO standard. Several innovations are further explored in bilateral collaborations and by industrial partners to assess their valorisation potential.
HyFiSyn’s key innovation is its interdisciplinary and holistic approach. It brings together materials scientists, mechanical engineers, polymer chemists and process engineers to jointly tackle the challenges in the field of fibre-hybrid composites. The emphasis on training ESRs to develop both modelling and experimental skills strongly differs from the traditional approach in this field and catalyse progress and increase the innovation capacity of the ESRs and the EU as a whole.

WP1: Simulation tools for microstructural design
KUL developed finite element models for debonding around fibre breaks, incorporated this into a longitudinal tensile failure model, and extended it to include fatigue damage. DTU used a model to correlate the experimental single fibre strength distribution to the strength of composites and found good agreement. KUL developed mesoscale models for the compact tension test, to better understand how the interaction between 0° and 90° plies governs crack growth. EPFL developed a mesoscale model to predict the translaminar fracture toughness based on measured bundle pull-outs. BMW developed macroscale models to better understand dynamic and quasi-static crash behaviour of hybrid car parts. UNott and NTPT developed process models to better understand fibre alignment and tow spreading processes.

WP2: Experimental characterisation for input and validation
KUL and DTU characterised the strength distribution of a range of glass and carbon fibres. KUL also characterised the stress-strain behaviour of two epoxy systems by performing tension and compression tests. Interfacial characterisation tests were planned but failed to materialise due to the pandemic. BME and EPFL measured relevant interlaminar and translaminar fracture toughness values. All these properties were used as input parameters in various modelling activities. A wide range of fibre-hybrid composites was tested in tension, bending and impact. This creates a large database of results that led to a better understanding of the mechanical behaviour of fibre-hybrid composites.

WP3: Manufacturing of novel microstructures
Tow-by-tow spreading was found easy to implement in existing processes, but the dispersion remains limited. NTPT revealed that calandering dissimilar thin ply prepregs is able to achieve excellent dispersion at a moderate cost. KUL developed an approach for 3D printing complex microstructures that are able to increase the translaminar fracture toughness of fibre-hybrid composites. Sioen used their looms to create custom hybrid weaves of self-reinforced composites hybridised with reinforcement fibres.

WP4: Smart & functional composites
Imperial developed morphing composites that have shape memory, controllable stiffness, and intrinsic heating. A proof-of-concept structure that was initially flat was able to deploy into a mesh. UVienna upscaled electrophoretic deposition strategies to create the anode and cathode. This yielded structural batteries and supercapacitors with improved energy storage capabilities. BME extended damage sensing capabilities compared to their existing patent, and improved interlaminar fracture toughness so that pseudo-ductile behaviour is achievable even for thicker plies. Intrinsic reparability was demonstrated in discontinuous layer hybrid laminates by thermoplastic film interleaving.

WP5: Recycling & alignment
Gen2Carbon undertook trials to better understand and optimise the use of pyrolysis for recovery of glass and carbon fibre from waste composite material. They also developed a separation method based on tribo-electrostatic charge to separate recycled carbon and glass fibres. UNott have upscaled and improved a rotating drum process to align short, discontinuous. This enables them to produce aligned fibre preforms at high production rates and with complex microstructures.

In addition to training 13 young researchers, HyFiSyn gained further insight into optimising fibre-hybrid composites, overcame some of the usual limitations of composites, and introduced new functions. Finally, recyclability of these materials was addressed and solutions were found to recover costly carbon fibres.