Extended projects: 2010 cohort
- Damage mechanics of fatigue delamination growth
- Damage progression and defect sensitivity
- Multistable orthotropic shell structures
- Novel mid span joints
- Microwave attenuation of structural composites containing ferromagnetic glass-coated amorphous microwires
- Biologically inspired body armour
- Simple numerical tools for assessment of impact damage
- An investigation of delamination and matrix crack interaction in composites failure
- Towards differential damage detection in composite materials
- Short fibre composite fabrication via additive layer manufacture: Evaluation of a concept
- Carbon nanotube sheets for multifunctional aerospace composite
- Moment-less states in shells under internal pressure with VAT (variable angle tow) derived orthotropy
Damage mechanics of fatigue delamination growth
Student: Jamie Blanchfield
Supervisors: Giuliano Allegri and Stephen Hallett
Composite structures have excellent in-plane strength, but are extremely weak through the thickness, and so they are prone to fracture at the interfaces between plies (delamination). Being able to model the onset and propagation of delaminations in composite structures experiencing fatigue loading is important to reduce the cost of experimental testing, and to this end the University of Bristol, supported by Rolls Royce, have been developing interface element formulations and fatigue damage accumulation laws for use within Finite Element Models.
This project aims, through numerical modelling, to validate (against previously obtained experimental data) a recently developed unified nonlinear damage evolution law for mode II fatigue damage onset and growth.
Damage progression and defect sensitivity
Student: Dominic Bloom
Supervisors: Kevin Potter, Jinhuo Wang and Chris Payne (Vestas)
Fibre waviness and wrinkling are recognised as some of the most common issues in the design and manufacture of industrial composite components. The aim of this project is to look at the effect of these defects on the performance of composite structures. A method which replicates the mechanism of formation of wrinkles is developed and used to generate representative specimens for tensile testing. Monitoring with Digital Image Correlation as well as Video Extensometry allows the initiation and progression of damage through the structure to be observed and understood.
Multistable orthotropic shell structures
Student: Broderick Coburn
Supervisor: Paul Weaver
Multistability in structures can be achieved via various mechanisms including anisotropy, pre-stressing, flexural rigidity tailoring and shell curvature. This project explores two case studies of multistability, namely tristability of an elliptic shell and bistability of the Venus flytrap both achieved with orthotropic doubly curved shells.
Achieving tristability of an elliptic composite shell by tailoring lay-up and initial curvature is explored with finite element analysis followed by the manufacture of a demonstrator. The Venus flytrap fast "snapping" mechanism is explained by a bistable theory, accounting for the geometry and orthotropic nature, both qualitatively and quantitatively using structural mechanics and finite element analysis.
Novel mid span joints
Student: Michael Elkington
Supervisors: Kevin Potter and Chris Payne (Vestas)
The latest generation of wind turbine blades are reaching a size where moving them by road is becoming almost impossible. This aim of the project is find a solution, in the form of the mid span joint which will allow blades to be built in two or more sections and assembled on site. Joining composite laminates on the scale seen here is rarely attempted, and the blades have a very demanding fatigue life. The task is complicated further as it is not possible to control the on site conditions sufficiently to use adhesives in the joining process. Several potential designs are currently being developed.
Microwave attenuation of structural composites containing ferromagnetic glass-coated amorphous microwires
Student: Jonathan Fuller
Supervisors: H-X. Peng and G. Hilton
The project involves the analysis of the microwave characteristics of polymer composites containing randomly dispersed short Fe-rich ferromagnetic microwires. The study has been performed in the X-band range (8-12 GHz) using a horn antenna. Wires are evenly dispersed within epoxy resin and on the top surface of each of the structural composites (CFRP, GFRP). Due to the GMI effect of the microwires, increased concentrations of wires will further reduce the reflection coefficient. The size and orientation of each sample is likely to affect the attenuation, and as such the edge diffraction effects have been accounted for in the data capture.
Biologically inspired body armour
Student: Mark Gilbert
Supervisors: Richard Trask and Stephen Hallett
Modern body armour design has evolved beyond the idea of a solid material and instead started to take lessons from nature's natural armour, such as nacre. Nacre is made up of a collection of random sized hexagonal tiles which are arranged within layers exhibiting a waviness pattern promoting the delocalisation of the energy upon impact. This project's intention is to recreate these mechanisms with synthetic materials and determine their suitability to be used as a new design philosophy for impact resistant body armour.
Simple numerical tools for assessment of impact damage
Student: Salah Muflahi
Supervisors: Stephen Hallett and Matt Jevons (Rolls-Royce)
Current high fidelity finite element analysis tools for impact assessment can be extremely complex and take a very long time to run. The main aims of this project are to create much simpler tools for the assessment of composite plates under impact and verify these against existing models and experimental results. As an early stage design tool, this can be used to save time and verify whether a given configuration is feasible. The tools to be developed will use MATLAB for closed-loop analytical solutions, extending results already available in open literature, and LS-DYNA for finite element analysis using shell elements and cohesive zone modelling.
An investigation of delamination and matrix crack interaction in composites failure
Student: Maria Francesca Pernice
Supervisors: Luiz Kawashita and Stephen Hallett
The interaction between delamination and matrix cracking in fibre reinforced composites is a critical mechanism by which cracks can join up and lead to ultimate failure. Here it is investigated, using a mode I test on ±45 and 60° angle ply laminates. Finite element analysis with a cohesive zone model was employed, to account for both the delamination between plies and matrix cracks. Matrix cracks were included at discrete intervals along the ply length. Double cantilever beam tests were then performed, to help better understand the physical failure phenomena. The model was able to capture the main features of the damage mechanism observed in the experiments, including migration from one delamination plane to another.
Towards differential damage detection in composite materials
Student: Steven Rae
Supervisors: Ian Bond, Duncan Wass and Richard Trask
Polymer shell microcapsules of varying diameter, containing solvent dyes with dissimilar fluorescence emission peaks, can be employed in the development of a system capable of providing differential damage visualisation and detection in composite materials. Key to indicating the severity of an impact is synthesis of microcapsules with a controlled and tunable diameter range; small capsules burst with higher impact loads and vice versa. By altering the agitation rate during synthesis the average microcapsule diameter can be controlled producing batches with specific size ranges. Different microcapsules can contain different coloured dyes thus a different signal can be detected depending on impact severity.
Short fibre composite fabrication via additive layer manufacture: Evaluation of a concept
Student: Marc Scholz
Supervisors: Richard Trask and Bruce Drinkwater
This project addresses the fabrication of new generation short fibre composites in the light of additive layer manufacture. Aiming to enhance the overall structural performance of currently available short fibre composites, the staggered fibre architecture of naturally evolving biological systems is adopted. Unable to realise such complex fibre constructs, given the current rapid prototyping methodologies, a wholly new approach is to be taken here. Specifically, external non-contact field gradient technologies are introduced to aid both orientation and positioning of reinforcement particles.
Carbon nanotube sheets for multifunctional aerospace composite
Student: James Trevarthen
Supervisor: Sameer Rahatekar
Carbon nanotubes (CNTs) have excellent properties on a molecular scale. Exploitation of these properties in composite materials, however, has been disappointing. Typically, CNT nanocomposites have been created by dispersion of CNTs in matrix resins. This is difficult and limited to a few weight-percent CNT. This project aims to produce hybrid composites of carbon-fibre and aligned CNT films (CNTFs), allowing greater volume-fractions of CNT, as well as control of directionality and placement. The manufacturing route developed is evaluated by examining manufactured quality of hybrid-laminates, as well as characterising interlaminar fracture toughness (mode I) and surface conductivity for comparison with traditional laminar composites.
Moment-less states in shells under internal pressure with VAT (variable angle tow) derived orthotropy
Student: Simon White
Supervisor: Paul Weaver
Under the action of internal pressure shell structures with a variable radius of curvature will usually develop bending strains; the severity of which depending on the rate of change of mid-plane curvature and the boundary conditions. A moment-less shell is a novel structure, designed to exhibit no bending effects under an applied loading.
Until now moment-less shells have been studied theoretically by: varying the mid-plane geometry, varying the shells thickness, and by varying fibre volume fractions. In this project the possibilities of attaining moment-less states in shells under internal pressure by varying the fibre trajectories are explored.