• Recycling of FRP wind blade waste material in concrete
• Intelligent composites forming - simulations for faster, higher quality manufacture
• Development of morphing fairing for semi-aeroelastic hinge winglets
• Nanocomposite excitonic superconductors
• Redesigning composite repair process using induction heating
• Digital engineering of space composites
• Investigation of porous composite materials for hydrogen storage
• Layer-by-layer manufacturing of complex composites
• Forming of thermoplastic prepreg with aligned High-Performance Discontinuous Fibre (HiPerDiF) for sustainable composite manufacturing

Recycling of FRP wind blade waste material in concrete

Student: Meiran Abdo
Supervisors: Eleni Toumpanaki, Andrea Diambra, Lawrence Bank (Georgia Institute of Technology)

The increased UK investments in the wind energy sector will result in an upsurge in the fabrication of wind turbines. Fibre Reinforced Polymer (FRP) wind turbines have a design life of approximately 20 years due to fatigue limitations [1] and a high volume of construction waste is expected from the offshore wind farms by 2050. FRP reuse strategies, such as the pyrolysis, focus on fibre retention with a particular interest in carbon due to the high value of the material [2]. Yet, these methods are more energy intensive and can often lead to damage and degradation of the fibres [2]. Mechanical recycling and use of FRP material as aggregate replacement or fibre reinforcement in concrete is an alternative method (downcycling) [3]. The mechanical properties of concrete with recycled FRP (FRPcrete) depends on the aspect ratio of the FRP needles with low aspect ratios, leading to considerable decrease in both compressive and tensile properties [3] and high aspect ratios resulting in superior tensile performance [4].

However, high aspect ratios of FRP needles can lead to agglomeration and porous concrete when a dense steel reinforcement cage is used on site in concrete structural elements. Fibre alignment in FRP needles plays a significant role in the tensile performance of FRPcrete and pultruded recycled FRP rods result in higher toughness via the crack bridging effect [4]. However, in FRP blades the fibre orientation changes within the same laminate (through thickness variation) and across the blade. Despite the majority of FRP blades being made of Glass Fibre Reinforced Polymers (GFRPs), Carbon Fibre Reinforced Polymer (CFRP) laminates can also be found inhibiting standardisation in the recycling process. To provide FRPcrete with reliable mechanical performance, other key aspects that need to be addressed are the durability of GFRP within the concrete alkaline environment and the structural integrity of the interfacial transition zone (ITZ) between the FRP needle and cement matrix that affects the concrete failure process.

The aim of the project is to assess both the short-term and long-term mechanical performance of FRPcrete for structural applications considering different variables (e.g. optimised geometry of FRP needles and aggregate replacement ratio). Both experimental and numerical work will be conducted using a validation and integration design approach. The end goal is to develop concrete that can effectively take advantage of the FRP wind blade waste.

Objectives

1) Find the optimum geometry (aspect ratio) of FRP needles and aggregate replacement ratio considering manufacturing limitations (steel reinforcement, concrete segregation and FRP needles agglomeration).

2) Find the optimum surface deformation of FRP needles (e.g. sand blasting and grooves) to increase the bond at the FRP/concrete interface.

3) Build an analytical model to predict the mechanical performance of FRPcrete considering variations in FRP needle geometry, fibre orientation, type of fibre (carbon and glass) and aggregate replacement ratio.

4) Assess the long-term performance of FRPcrete by conducting both permeability and mechanical tests.

5) Address size effects and the mechanical performance of large-scale beams.

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Intelligent composites forming - simulations for faster, higher quality manufacture

Student: Siyuan Chen
Supervisors: Jonathan Belnoue, Stephen Hallett, Adam Thompson, Tim Dodwell (University of Exeter)

Liquid composite moulding (LCM) techniques are a cheaper alternative to other composite manufacturing methods such as prepreg and autoclave moulding. Prior to the infusion phase, the dry fibrous reinforcement, which is typically difficult to handle, is formed to shape. Forming is a cheap and productive approach to handle the preformed fabric, however, the nature of fibrous reinforcement materials makes them highly susceptible to variation during the forming process. The variation, including aspects from geometry of tool, forming control, and material itself, may lead to a different level of defect, such as wrinkles and bridges.

To optimize the forming process, the finite element (FE) modelling approach has been explored to assist prediction and optimization, and has been able to simulate relatively complex component in a good accuracy. However, these models are typically time-consuming, especially for iterative design optimization. Thus, it will be meaningful for industry application to develop a quick method to evaluate the parameters (including material and geometry) of forming process to avoid unacceptable defects. Furthermore, a major challenge in FE modelling is to account for these variabilities into the simulations, so that the statistical spread of possible outcomes is considered rather than a single deterministic result. To achieve this, a probabilistic modelling framework is required. Machine learning (ML) is a possible direction for developing such a surrogate model framework based on learning from simulation data, which could skip time-consuming modelling process as well as provide a quantification to the variances and uncertainty. In the long run, this would allow the construction of a fully autonomous forming rig with embedded sensors and active controls where the manufacturing conditions are adapted on the fly and defect formation mitigated based on rich live experimental data feeding into real-time simulation and optimization of the process.

This project aims to explore an intelligent way to optimize and accelerate our computer assistant modelling tool which simulates the textile forming process. A machine learning (ML) based surrogate model is being developed, which aims to provide live prediction to fabric forming industry. This surrogate model is to be trained by a set of data points generated by FE model, thus in the first step a property FE constitutive model is selected for forming simulations. A shell-membrane hybrid FE modelling tool is adopted to simulate the behaviour of textile during forming on an industry-inspired tool. A series of springs or other controlling method will be adopted to adjust the forming controls in the FE model, in order to simulate the different wrinkling and bridging level under different forming parameters. In current research, the positions and stiffnesses, together with the pressure applied on the top, are regarded as input parameters and can be modified to control the deformation of textile during forming. By providing a set of combinations of input parameters, hundreds of simulations will be conducted to obtain a data set, which will be used as the training set for surrogate model.

The Gaussian Process Regression (GPR) method is used to develop the surrogate model, for its applicability on small data set problem. On the other hand, GPR method naturally features uncertainty quantification ability, which can be used to predict and quantify the potential variances in the forming process. In this project, a GPR emulator will be developed and tested by rich simulation and experimental data. In the future, this method will be developed as a tool for our industry partners, which is expected to greatly reduce forming defects as well as shorten the parameter test period.

With the maturation of this surrogate model, the model together with the entire method can be compiled into software and integrated in forming process equipment in the future. With the use of sensors, real-time parameters such as the local temperature, tensile force, and shear angle of fabrics and moulds can be detected and collected during the process. By importing these real-time data into the surrogate model, the software can calculate the point with the highest probability of producing the optimal result, so that the forming rig can fine-tune the control parameters to optimize the quality of the forming.

This technology can not only be applied in the forming process. In the various steps of composites part production, such as compaction, curing or AFP layup, this technology can be used for real-time optimization of processing quality. It can be said that this technology is an important way for the intelligent upgrading of the manufacturing industry.

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Development of morphing fairing for semi-aeroelastic hinge winglets

Student: Nuhaadh Mahid
Supervisors: Ben Woods, Brano Titurus, Mark Schenk, Tom Wilson (Airbus)

In recent years, increasing emphasis has been placed on reducing aircraft emissions. One of the well-understood approaches to reduce emissions in civil aircraft is to increase the wingspan. This reduces the induced drag of the wing, hence, the fuel consumed. Two major constraints in the way of this approach are (1) the limited airport gate sizes and (2) the increased structural requirement of a longer wing.

The Semi-Aeroelastic Hinge concept is aimed at circumventing the above-mentioned two challenges by having a folding wingtip where the folding axis is at a flare angle outward to the freestream direction. The folding of the wingtip allows the aircraft to shorten the wing before approaching the airport gate and the flare angle allows the wing to reduce the maximum gust load on the wing root. Previous research in the literature has shown that the best gust load alleviation is achieved for wingtips with low folding stiffness, damping and mass along with a high flare angle.

One of the challenges in the physical realisation of such a device is the discontinuity of the wing skin between the inboard wing and the wingtip. This discontinuity of the surface is prone to the generation of vortices and the subsequent flow separation which erodes some of the aerodynamic benefits of the foldable wingtip. A compliant fairing around the joint will close the gap while allowing for the folding of the wingtip. This fairing could be an integrated primary structure that also acts as the joint; or a secondary skin around a hinge joint, which only carries the aerodynamic load. The choice of the latter is based on space efficiency and minimising the folding stiffness for better gust load alleviation.

This research project focuses on (1) studying the behaviour of the skin on a folding wing geometry and identifying the properties of the skin which optimise the desired characteristics, (2) identifying the architecture of skins that has the desired properties and (3) implementation of the identified skin architecture on a folding wingtip device.

In summary, the overarching research question could be summarised as “What benefits can compliance-based, stiffness tailored, morphing fairings provide to full-scale commercial airliners with Semi-Aeroelastic Hinge winglets?”.

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Nanocomposite excitonic superconductors

Student: Rikesh Patel
Supervisors: Simon Hall, Chris Bell, Steve Eichhorn

Around 60 % of all electrical energy generated worldwide is lost to resistive heating of transmission wires, leading to more fossil fuels being needed to make up the shortfall, and hindering the use of green alternatives. With the ability to transmit electricity with zero electrical resistance, superconducting wires would resolve the problem of resistive losses in the grid. However, this is not yet realised since current superconductive technologies require cryogenic cooling to function. It, therefore, remains a holy grail of the technology to realise superconductivity at ambient temperatures and pressures. This project aims to realise such a material by making a nanocomposite between transition metal dichalcogenides (oxygen group element) and carbon.

In this project, first nanoparticles of WSe­2 and TiSe2 will be made and characterised by a suit of characterisation methods including, Ultraviolet and Visible Light Spectroscopy and Transmission Electron Microscopy (TEM). These nanoparticles will then be composited with carbon. Initially, functionalised (with metallophilic functional groups on the surface) carbon fibres will be used with the goal of ‘sticking’ the particles to individual carbon fibres. These will then be tested for superconductivity using a Superconductive Quantum Interference Device (SQUID), the gold standard for these tests.

The outcome of this project has the potential to revolutionise not only how electricity is transmitted but also how it is generated.

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Redesigning composite repair process using induction heating

Student: James Uzzell
Supervisors: Dmitry Ivanov, Laura Pickard, Ian Hamerton

The application of advanced composite materials in the aerospace industry, utilised for their superior mechanical properties, has grown exponentially over the last few decades. The largest limitation of these materials from both an economic and sustainability viewpoint are the inability for time and energy efficient repair. Traditionally, damaged plies are replaced with laminate patches or wet lay ups followed by a long cure cycle over the entire component. Therefore, there is a requirement for a more localised curing method which can produce repair patches cured in-situ in a fast and energy efficient manner.

To achieve this, induction heating will be testing by volumetrically heating composite laminates to gain a better understanding of its effects before producing repair patches cured in-situ. Preliminary experiments have achieved rapid heating in carbon fibre based laminates as well as glass fibre laminates containing metallic tufts. These experiments show heating patterns to be highly dependent on the geometry of the induction coil used. There is also a significant non uniformity in the heating of a composite panel both in plane and through thickness which could be improved using novel induction coil geometries as well has highly conductive susceptors.

This research aims to optimise the process of induction curing both in terms of rate of cure and uniformity of heating profile. Numerical modelling using the electromagnetic capabilities of Finite Element software, Abaqus, will form the basis for understanding the effect of coil geometries and materials parameters on the heating profile. These models will be used to manufacture an induction coil followed by an optimisation process to cure laminates quickly with high uniformity. This optimised process will be used to manufacture repair patches which will be compared to conventional methods.

The key objectives of this project are:

• Perform an optimisation of design variables to maximise the efficiency and uniformity of inductive heating using Finite Element modelling.
• Manufacture composite laminates using optimised process based on modelling.
• Apply experimental methods to produce repair patches cured in-situ.
• Manufacture composite laminates using optimised process based on modelling.

The results of this work should allow manufacture of composite repair patches which can be cured in situ which will allow for repair of large laminate components significantly more time and energy efficient manner.

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Digital engineering of space composites

Student: George Worden
Supervisors: Ian Hamerton, Kate Robson-Brown, Sebastien Rochat

The aim of this project is to create a method to estimate the degradation of materials in hostile environments. Hostile conditions such as space or the deep sea make it difficult to actively monitor how a material or structure is performing. More accurate estimation of a material’s life cycle in such conditions lead to more efficient designs that are better suited to the intended application.

The primary method used in this project will be to create a digital twin model for a number of composite laminates that are to be sent to the International Space Station (ISS) and exposed to space. The composite laminates will be sent to the ISS in April 2021 and then be exposed on the Bartolomeo platform for 6 months as part of a project with the European Space Agency (ESA). Following exposure, the samples will be returned to Earth where they will be reanalysed to quantify the effects of LEO exposure on the material. This information can then be used to update the computer model.

The computer model will be created using data collected through analysing sample laminates using a variety of imaging, thermal, and mechanical techniques such as optical microscopy, CT scanning, and mechanical testing. The data analysis and model building will be done in cooperation with the Jean Golding Institute which is involved in data science and data-intensive research at the University of Bristol.

Conditions in low earth orbit (LEO) such as those present around the ISS are very hostile, particularly to polymer materials like those in the matrix of fibre-matrix laminates. The hazard that will be focused on in this project is the presence of atomic oxygen from the upper atmosphere. This oxygen oxidises the surface of the materials in LEO, leading to erosion and loss of material which could lead to a loss in material performance. Other significant hazards in LEO are high-energy radiation and impacts by micrometeoroids. It may be possible do some ballistic testing to simulate impact and build this into the digital twin as well. The matrix material used for this project is a novel polybenzoxazine polymer mixed with polyhedral oligomeric silsesquioxane (POSS). The benzoxazine polymer provides improved mechanical and thermal performance compared to standard aerospace epoxies while the addition of POSS has been shown through previous research to increase resistance to atomic oxygen erosion in polymeric materials.

Ultimately, it is hoped that this model could be used to add functionality or develop new materials for use on structures in low earth orbit. Later in the PhD project, once the digital twin model is complete, self-healing functionality will be added to the benzoxazine-POSS material using the Diels-Alder self-healing system.

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Investigation of porous composite materials for hydrogen storage

tudent: John Worth
Supervisors: Charl Faul, Valeska Ting

The depletion of traditional fossil fuels on such a comprehensive scale has led to calamitous global climate change and severe environmental concerns. Hydrogen is a promising candidate to replace existing finite petroleum-based energy sources because of its remarkable gravimetric energy density, clean combustion and abundance. However, the storing of hydrogen presents significant challenges because of its low volumetric density at ambient temperatures. Currently, the industry standard for storage is to highly compress hydrogen at ambient temperatures. This strategy suffers from eventual compression losses and demands lightweight, mechanically high performing and costly containment structures.

Nanoporous materials have demonstrated the ability to adsorb hydrogen allowing for it to be stored at high densities under specific conditions; often extremely low temperatures, high pressures, or both. As a result, their application to systems that require more modest working conditions (such as transportation applications) has been restricted. Designing and conceiving materials for adsorption that can successfully store and relinquish hydrogen at ambient conditions continues to be an important challenge.

A specific class of nanoporous polymer known as conjugated microporous polymers (CMPs) exhibit highly cross-linked three-dimensional porous networks in an amorphous fashion that results in both high thermal and chemical stability. CMPs have been used in a range of applications, including the adsorption and capture of  gases  such as carbon dioxide, but their hydrogen storage capabilities have received considerably less attention. This project aims to investigate the potential of CMPs and composites formed from these materials for safe and efficient hydrogen storage.

Design and synthesis of a range of CMPs using an established metal catalysed cross-coupling reaction (Buchwald—Hartwig coupling) will be conducted before characterisation of the physical properties of the resulting material using standardised techniques including gas sorption analysis (to determine specific surface area, pore volume and pore size), thermogravimetric analysis, X-ray diffraction, ultraviolet-visible spectroscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy and transmission electron microscopy.

Selected high performing CMPs may be blended with various matrices to form a composite that offers numerous advantages over the raw powdered counterpart in terms of safety, handling and practical manufacturing. An evaluation of the performance of these materials in the composite form will be conducted, including an assessment of their stability and mechanical properties, in order to conclude if these materials could contribute to the hydrogen storage field by either increasing hydrogen storage capabilities or decreasing the required operating pressure in hydrogen storage vessels and ultimately contribute towards carbon neutrality/net zero.

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Layer-by-layer manufacturing of complex composites

‌Student: Axel Wowogno
Supervisors: James Kratz, Iryna Tretiak, Stephen Hallett

Autoclave moulding is one of the commonly used processes by the aerospace industry to manufacture low weight and high-performance composite parts. This manufacturing process is a robust and well-established production method that offers satisfactory consolidation and supresses defects formation, by applying high pressure and temperature. However, it involves high capital and operation costs, as well as long cycle times, creating process bottlenecks. That is why a cost-effective and more versatile process is in a high demand by manufacturers.

Vacuum-Bag-Only (VBO) consolidation is one of the available Out-of-Autoclave (OOA) techniques that is under consideration to replace autoclave moulding using a new generation of OOA prepregs. Even without the autoclave, an additional oven moulding step after the material deposition, often performed via Automated Fibre Placement (AFP), is nevertheless still necessary. There is hence a need for a novel method that tackles altogether the issues of process rate, cost, energy use, and part performance.

The main goal of this PhD is to develop a new single-stage additive manufacturing process by combining material placement, consolidation and curing of thermosetting composites. To achieve this, several objectives must be considered:

• Materials: Investigation of materials behaviour and selection of the suitable material for layer-by-layer curing.
• Manufacturing process: Development of a procedure and selection of suitable process parameters, i.e. contact time, temperature, deposition speed and pressure.
• Part quality: Investigation of the mechanical performance of the manufactured samples, achieved via defect analysis and mechanical testing.

This project is supported by Rolls-Royce.

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Forming of thermoplastic prepreg with aligned High-Performance Discontinuous Fibre (HiPerDiF) for sustainable composite manufacturing

Student: Burak Ogun Yavuz
Supervisors: Jonathan Belnoue, Marco Longana, Ian Hamerton

Although composite materials can play a role part in the decarbonisation of transport, through structure lightweighting, they are inherently challenging in terms of sustainability. This is because the high-performance composites used in the aerospace and automotive sector are often made of carbon fibres and thermosets resins that are difficult to recycle.

The HiPerDiF (High-Performance Discontinuous Fibre) method, invented at the University of Bristol, offers a way to remanufacture composites from reclaimed fibres. The method allows the production of composites comprising high-volume fractions of highly aligned discontinuous fibres, with high processability and performance. Still, greater sustainability credentials can be gained by using thermoplastic matrices which have a greater potential for recycling.

This study aims to develop a forming simulation tool for the manufacturing of thermoplastic HiPerDiF tapes, which are composed of 3mm long carbon fibres and PLA matrix. The tool is expected to be validated by forming experiments. This can help in the development of a robust manufacturing process for the highly formable HiPerDiF thermoplastic matrix tapes.

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