PhD projects 2012 cohort
- Novel morphing structures for aerofoil flow and noise control purposes
- 4D materials: programming reversible shape change into hydrogels
- Tailorable energy absoprption using 3D printed thermoplastic polyurethane honeycombs
- The application of piezoelectric sensors to composite materials
- Light and chemistry applied to the control of smart materials and structures
- Chlorhexidine-phosphate salts in wound care; the development and testing of antimicrobial functionalised materials
- Aerolastic tailoring of aircraft wings using structural geometric features
- Composite armour - from atoms to application
- On laminators in composite design and manufacture
- Additive manufacture of composite materials with ultrasonically assembled reinforcement microstructure
- Multi-scale characterisation and modelling of tufted composites
- Investigation of aligned short fibre reinforcements for manufacturing high-volume and geometrically complex components
- Structural design of variable stiffness composites laminated on doubly curved surfaces
Novel morphing structures for aerofoil flow and noise control purposes
Student: Qing Ai
Supervisors: Mahdi Azarpeyvand and Paul Weaver
Aerodynamic noise has remained the most significant cause of adverse community reaction related to the operation and expansion of airports and wind-farms, and is still an obstacle to the application of some new technologies, such as contra-rotating propellers. The state-of-art of airfoil noise reduction relies mainly on some passive methods, such as trailing edge serrations, porous materials, etc. the most important aspect of this research is to introduce and investigate the concept of morphing aero-structures for aero-acoustic purposes, which can actively manipulate the flow pattern around the airfoil.
The aim of this research is to further understand and improve the design philosophy of morphing aero-structures considering their targeted performance. Methods used in this analysis include semi-empirical airfoil self-noise prediction model, analytical method and also FEA method for the prediction of the mechanical behaviour of the morphing structures. Demonstrators will be built for experimental investigations of both the flow behaviour and mechanical behaviour of the morphing structures.
4D materials: programming reversible shape change into hydrogels
Student: Anna Baker
Supervisors: Duncan Wass and Richard Trask (University of Bath)
This project will use a novel polymer network that will remodel under mechanical stress by using heterocyclic mechanophores as crosslinkers. And aims to use a variety of different mechanical forces to cause the mechanophore to undergo retro-cycloaddition breaking the crosslinks. The mechanophore will then be formed through cycloaddition using an embedded catalyst creating a reformable polymer network. This polymer is proposed to be used to mitigate against the initiation and development of critical and sub-critical damage in composite materials.
Tailorable energy absoprption using 3D printed thermoplastic polyurethane honeycombs
Student: Simon Bates
Supervisors: Ian Farrow, Richard Trask (University of Bath), Steve Austen (RNLI) and Holly Phillips (RNLI)
The Royal National Lifeboat Institution (RNLI) is seeking to develop multifunctional materials and structures to enhance fleet and personnel performance and safety. One challenge is crew safety to extreme operational environments. To protect the crewmembers in these situations, it will require the integration of novel functionalities for a range of real operational conditions. Realistically, to meet this aim will require the development of new design and materials integration, whilst considering the operational demands upon the crew member. Ideally the new ‘multifunctional composite’ system will offer better agility (i.e. lower physiological burden), better integration, multi-protection for environmental survivability and be ‘intuitive’.
The application of piezoelectric sensors to composite materials
Student: Jamie Chilles
Supervisors: Anthony Croxford and Ian Bond
The increasingly common use of composites for crucial aerospace components has resulted in an urgent desire to increase the ability to inspect such components. Currently components are typically designed on the basis of being able to tolerate any damage that cannot be detected reliably with visual methods. The result being that structures are designed very conservatively.
This project will look at an alternative approach where a network of sensors is permanently embedded in a composite structure and periodically interrogated to provide information about its current state. In doing this the structure can be designed to be significantly lighter and closer to its ultimate performance. The approach employed in this project is to embed conventional piezoelectric ultrasonic transducers into a structure and connect to them using inductive coupling. Thus an inspector can potentially move an inspection “wand” over the structure making ultrasonic measurements automatically as it passes over embedded sensors and determine the condition of the structure.
The objective of this research is to develop experimental and numerical techniques to assess the effect of embedding sensors within composite laminates using different strategies. In addition the performance of the sensors under thermal and mechanical loading will be analysed, to identify temperature compensation for the embedded sensors and characterize sensor performance in an operational structure.
Light and chemistry applied to the control of smart materials and structures
Student: Michael Dicker
Supervisors: Ian Bond, Paul Weaver and Jonathan Rossiter
This research is concerned with the integration of the functions of sensing and control within structures composed of self-actuating composites. The aim of doing so is to create a new class of sentient structure which can intelligently change their orientation or configuration in response to their environment. Such a system would mimic the distributed sensing and solid state actuation so often seen in nature, resulting in robust, highly reliable multifunctional structures. The initial focus of this work will be on the development of a novel self-actuated structure, composed of a hydrogel core flexible matrix composite. In the future such devices could find application in solar power generation, efficient aerospace structures and soft robotics.
Michael was awarded a Faculty of Engineering Commendation for his thesis.
Chlorhexidine-phosphate salts in wound care; the development and testing of antimicrobial functionalised materials
Student: Peter Duckworth
Supervisors: Michele Barbour, Sameer Rahatekar and Valeska Ting
Chronic wounds with prolonged healing times are very vulnerable to infection which frequently results in amputation; to counter this - this project aims to offer a multifunctional wound dressing material which has embedded antimicrobial action.
Novel antimicrobial nanoparticles, developed and patented by the Oral Nanoscience Group at the University of Bristol, have been incorporated within a natural polymer matrix to create a nanocomposite suspension from which thin films and electrospun fibres have been manufactured.
These materials have been fully characterised by various microscopies and the nanoparticles, which have been found to survive the material processing, are evenly distributed throughout the matrix. Elution of antiseptic from this material into an aqueous environment occurs over at least a two week time period and shows a dose dependant response.
Antimicrobial work has demonstrated the material is fit for purpose – being effective against the most common organisms to infect wounds. Current work is investigating any effect this material may have on the ability of a wound to heal naturally.
Other current work involves a novel 3D printed low shear, continuous flow biofilm reactor which has very recently been designed, prototyped and manufactured. This allows more complex microbiology experiments to be run, obtaining more relevant results by mimicking a real wound environment whilst still being a simple and inexpensive setup.
Aerolastic tailoring of aircraft wings using structural geometric features
Student: Guillaume Francois
Supervisors: Jonathan Cooper and Paul Weaver
The aeroelastic performance of a wing, including static aeroelastic shape, flutter/divergence speed and gust load response, has a significant influence on aircraft design. The control of aeroelastic performance, also known as aeroelastic tailoring, therefore offers potential weight savings. Aeroelastic tailoring is made by controlling the wing’s bending and torsional stiffness and the ability of the wing to twist under bending loads. This project investigates the effect of three internal structural geometric features (e.g. arrangement, shape and cover thickness) of a conventional wing structure composed of spars, ribs and covers on the wing’s stiffness and bend-twist coupling using the entire 3D aerodynamic shape to improve aeroelastic performance. In order to quantify the effect of different structural concepts on aeroelastic performance a thorough approach based on Finite Element (FE) modelling and various load cases is developed. Finally, experimental validation of the FE trends found with the structure arrangement is attempted using wings made from additive layer manufacturing.
Composite armour - from atoms to application
Student: Mark Hazzard
Supervisors: Stephen Hallett, Richard Trask (University of Bath), Paul Curtis (DSTL) and Lorenzo Iannucci (Imperial)
The aim of this research is to generate an enhanced experimental and analytical understanding for the potential of novel composite structures at absorbing energy in dynamic high strain rate environments during impact events. Composites themselves are traditionally used due to their excellent specific properties, however recently they have also been exploited to absorb large amounts of energy under impact such as in Formula 1 for crashworthiness. There have also been developments in the production of ultra-high molecular weight polyethylene (UHMWPE) fibres to absorb large amounts of impact energy at high strain rates through elastic deformation. It is envisaged that a material configuration can therefore be designed from the nano-scale upward across multiple length scales to further improve composite high strain rate performance. A materials development and testing program is therefore required in this project as well as theoretical modelling work through explicit finite element analysis to understand and optimise novel material architectures to maximise impact performance.
The image shows a finite element model of a ballistic impact on a Dyneema® composite showing partial perforation of the laminate.
Mark was awarded a Faculty of Engineering Commendation for his thesis.
On laminators in composite design and manufacture
Student: Helene Jones
Supervisors: Kevin Potter and Carwyn Ward
This work is an investigation into the design process for batch of one composite products. The freedoms offered by composite materials will be explored in the context of unconstrained applications. The aim is to contribute to an interdisciplinary language defining clarity on what design for composites means. The methodology framework implemented will be based on the assumption that both materials and fabrication processes contribute to the development of a product. How motivations, such as performance properties and conceptual ideas, inform the design process in this framework will be studied. An experimental approach will be adopted to produce physical prototypes. These will validate the methodological framework used to conduct this research.
Additive manufacture of composite materials with ultrasonically assembled reinforcement microstructure
Student: Thomas Llewellyn-Jones
Supervisors: Bruce Drinkwater and Richard Trask (University of Bath)
Due to the manufacturing issues inherent with continuous fibre composites, a number of different methods have been developed to produce short fibre composites with comparable material properties. Short fibre composites currently have no mechanism for effective load transfer from the matrix to the fibres, and so their materials are largely matrix dominated. Acoustic radiation forces have previously been used to produce short fibre composites, but only in small samples, and the aim of this work is to develop a suitable manufacturing process to continuously form such materials. In order to enhance matrix-reinforcement stress transfer, the aim is to stagger hierarchical fibres developed within ACCIS, consisting of glass microfibres with Zinc Oxide nanorods grown on their surface. To maximise control of the reinforcing fibres, other field effects will likely be used in conjunction with acoustic radiation pressure.
Multi-scale characterisation and modelling of tufted composites
Student: Camilla Osmiani
Supervisors: Ivana Partridge, Giuliano Allegri (Imperial College London), Galal Mohamed and Victoria Coenen (Rolls-Royce plc)
Multi-scale modelling is gaining increasing interest in the aerospace industry of composite materials and has been identified as the tool that could accelerate the certification of through-thickness reinforcements for the control of delamination in composite structures. The application of this technique to z-reinforced composites requires a deep understanding of the mechanisms of delamination bridging, characteristic of each type of microfastener (Z-pins, stitches and tufts the most common), at various length scales. This project focuses on the multi-scale characterisation and modelling of tufted composites. Specific preform architecture, tufting thread and resin system were selected for this study: biaxial carbon NCF, twisted continuous carbon fibre thread and low cure temperature epoxy. Mechanical tests on pre-delaminated single-tuft cuboidal specimens were carried out to identify the response of tufts to tension, shear and mixed tension-shear loads. Micrographic analysis and x-ray computed tomography were used for the morphological characterisation of tufts and the identification of their failure mechanisms. This experimental data informed the development of a novel analytical mode I constitutive model for tufts. The objective of the model was the simulation of a stress-displacement law (or cohesive law) to be implemented into predictive meso- and macro-scale models of tufted composites. Meso-scale models of tufted fracture coupons were developed via the Cohesive Zone Modelling (CZM) technique. The challenges associated with using cohesive elements to predict the large-scale bridging responses of tufted interfaces were analysed and discussed. The developed meso-scale models were validated against experimental data on tufted Double Cantilever Beam (DCB), End Notch Flexure (ENF) and Mixed Mode Bending (MMB) fracture coupons, with encouraging results. The purpose of the presented multi-scale modelling strategy was to catalyse further modelling development and provide design guidelines to help tufting reach a level of technology readiness comparable with that of Z-pinning.
Investigation of aligned short fibre reinforcements for manufacturing high-volume and geometrically complex components
Student: Matthew Such
Supervisors: Kevin Potter and Carwyn Ward
The current methodologies employed to manufacture composite components still lack sufficient rate to meet demand, furthermore, state of the art automated processes impose restrictions on component geometrical complexity. Many of these restrictions arise directly as a result of the use of continuous fibre reinforcements, making a detailed investigation of discontinuous fibre forms an opportune research topic at this time. The tensile stiffness, strength and failure strain of aligned discontinuous fibre composites are similar to those of continuous fibre composites, provided the fibres are accurately aligned and their length is sufficiently long compared to the critical fibre length. Processing of highly-aligned discontinuous fibres may avoid many of the manufacturing defects induced in continuous fibre architectures, while allowing for similar mechanical properties. The future will allow for faster and simpler forming operations and better use of in process scrap. In this DTC PhD project, the focus will be on understanding the manufacturability of highly-aligned discontinuous fibre structures and designing methods to cope with high-volume manufacturing of geometrically complex components.
Structural design of variable stiffness composites laminated on doubly curved surfaces
Student: Matthew Thomas
Supervisors: Paul Weaver and Stephen Hallett
This research developed methods for designing variable stiffness composite laminates to further improve the structural design of composite fan blades in jet engines. Variable stiffness laminate design in literature has been limited to structures of zero to little curvature in only one direction, such as cylinders. In this research, a novel method for designing fibre paths of variable angle tow (VAT) plies on to doubly curved surfaces were developed.
Lamination parameters convert laminate stiffnesses to a convex and continuous design space, while also decreasing the number of design variables needed to define laminate stiffness. This makes stiffness optimisation via gradient-based optimisers a fast and efficient process. Spatially varying lamination parameters were used to varying the laminate stiffness over the part. The optimal variation of lamination parameters for a variable stiffness and thickness fan blade were found through gradient-based optimisation. Results show a 40.2% and 9.3% reduction in strain energy compared to a quasi-isotropic (QI) and the optimal constant stiffness laminates, respectively. The tow paths and ply shapes of every VAT ply were subsequently found using a two-stage optimisation process to minimise the difference between the VAT laminate and the optimal lamination parameter variation.
Bend-twist coupling has been extensively researched for wind turbine applications as a means of shedding load and improving turbine performance in response to sudden changes in wind speed during turbulent wind conditions. The use of stiffness coupling terms, such as extension-twist and bend-twist, to produce to a fan blade that can passively increase blade angle difference between representative takeoff and cruise conditions was investigated.