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

Periodic Reporting for period 1 - HyFiSyn (Hybrid Fibre-reinforced composites: achieving Synergetic effects through microstructural design and advanced simulation tools)

Reporting period: 2018-06-01 to 2020-05-31

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 will therefore develop 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 taken into account for accurate predictions. The process simulation tools will also help gaining better control of the manufacturing and hence the microstructure. HyFiSyn’s research programme therefore has four objectives:
• To develop simulation tools to predict synergies and to support changes in manufacturing;
• To fundamentally understand the 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 are brought together to jointly tackle these challenges. The academic partners will develop advanced simulations tools, perform dedicated experiments to validate those tools and explore new concepts for maximising synergetic effects and achieving smart and functional composites. The material manufacturers will enhance their existing technologies to better suit the needs for fibre-hybrid composites. The end users will adopt their design procedures to structural parts in fibre-hybrid composites and to optimally exploit synergetic effects. Additionally, they will provide an industrial perspective for the developed technologies, and ensure that the research develops in the right direction.
HyFiSyn is currently about half-way in the project, and has already led to significant results. To name just a few of the main results:
- A fatigue model was developed that predicts the full fatigue life diagram based on realistic micromechanisms.
- A finite element model was developed to predict the stress redistribution around fibre breaks, including debonding, thermal stresses and friction.
- A microstructure generator was developed for short, aligned fibre composites.
- Extensive tensile tests were performed to find a reliable methodology for measuring the strength of UD composites.
- New tools for automatically analysing the microstructre of hybrid composites were developed.
- Novel thin ply prepregs and textiles were manufactured and characterised.
- Functionalities, such as morphing, damage sensing and energy storage, were introduced through fibre-hybridisation.
The key innovation of HyFiSyn lies in 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. These different backgrounds provide a unique opportunity to catalyse the state of the art. Many researchers in the field of composites are either modelling experts or experimentalists, but few of them are both. The strong emphasis on training ESRs to develop both modelling and experimental skills hence strongly differs from the traditional approach in this field. The HyFiSyn consortium is convinced that this approach is essential to catalyse progress and increase the innovation capacity of the ESRs and EU as a whole.
The research programme contains a wide variety of innovations in terms of design tools, experimental setups, functionality and processing.

Microstructural design tools will be developed that capture synergetic effects and can optimise the microstructure. These synergies will then be brought to larger scales through a multiscale approach. Secondary damage will be accounted for in multiscale mechanistic models to capture the volumetric extension of the damage process zone in hybrid laminates. New macroscopic strength and fracture models will be established by homogenisation to build physically sound, scale-independent models for strength and fracture. HyFiSyn develops process simulations to gain a better control over the microstructure, so that the designed microstructures can be manufactured.

HyFiSyn will employ advanced characterisation techniques to experimentally validate internal damage development rather than just final failure. HyFiSyn uses the damage development in tension and flexure as a starting point to understand more complex loading scenarios, such as compression and fatigue. By using micro-computed tomography and high resolution microscopy, the detailed 3D damage process zone will be analysed and secondary damage will be quantified. Fracture parameters will be determined by matching parametric finite element predictions to the displacement field measured by state-of-the-art characterisation techniques.

HyFiSyn explores intrayarn configurations in three ways: (1) the traditional comingling route, (2) the alignment of recycled, short fibres and (3) simultaneously spreading two fibre types. The risk-gain balance for these three strategies is low-low, low-high and high-high, respectively. Process parameters will be determined and models will be developed to better understand what controls the spreading quality of prepregs, and apply that knowledge to develop new thin ply prepregs. HyFiSyn strives for a more holistic approach: the spreading and curing parameters are looked at simultaneously, leading to a cured composite with optimal performance.

HyFiSyn investigates how the additional design freedom in fibre-hybrid composites can be exploited to create smart features and added functionality such as morphing, energy storage, self-monitoring and self-healing in composites. HyFiSyn will investigate how incorporating fibres within the thermoplastic can improve the mechanical properties of the interleaved composite and how the controllable stiffness and shape memory capabilities are affected. In addition to improving the mechanical properties, HyFiSyn will investigate the use of additional reinforcement in the thermoplastic layer as a resistive heating element to control the stiffness loss and shape recovery process. HyFiSyn develops mingling strategies to finely disperse the anode and cathode, and scale up energy storage technology.

HyFiSyn will evaluate the best approach for dealing with hybrid waste streams by investigating ways to remove the glass fibres from the waste stream. HyFiSyn also develops technology to align discontinuous, recycled fibres to manufacture hybrid composites with highly aligned structures comprising various fibre lengths and a wide range of different fibre fractions. Process tools will be developed to gain better control over the process.