PhD Projects for 2023 Entry

2023 entry fully-funded PhD projects are currently being finalised, and links to job adverts will appear here as they come online. If you are interested in joining us for the 2023-24 academic year, we would be happy to have a chat and provide more information

Developing a microscale split Hopkinson pressure bar (Dr D Williamson)

The strength of metals increases with deformation rate. Knowing by how much, and arguably more importantly why, are important considerations and questions in the fields of engineering and condensed matter physics.

A split Hopkinson pressure bar (SHPB) is an instrument that acts as a mechanical waveguide and is typically used to deform samples of materials at strain rates of order 10^3 per second. Miniaturization, of both the instrument and samples, is key to achieving higher strain rates. Using a so-called mini-SHPB we have had a great deal of success studying such materials as polycrystalline copper at strain rates of 10^4 to 10^5 per second.

Taking the next logical step, this experimental PhD project addresses the novel and technically challenging problem of developing and utilising a microscale split Hopkinson pressure bar for the study of single crystal and small grain size polycrystalline materials in uniaxial stress compression at extremely high strain-rates; in excess of 10^6 per second. This is a loading regime of importance in the development of physics-based materials models which is not directly accessible by other research techniques. The material to be studied will primarily be the bcc metal tantalum in single crystal form along specific loading axes (i.e., the principal crystal orientations) and the data will used for the development and validation of dislocation mobility and strain-hardening laws employed in mesoscale (grain-level) crystal plasticity simulations.

****************************************

Some examples of other possible PhD projects (which do not currently have specific funding sources attached) are given below

Effect of structure on dynamics of geological materials (Dr C Braithwaite / Dr James Perry)

The dynamic mechanical response of geological materials is of great importance, both industrially and scientifically, with applications ranging from seismology and planetary impact, to oil exploration and mining. The materials themselves are often complex and polycrystalline with a variety of constituent minerals and wide range of inherent length scales. While significant research has been conducted in the field, currently there is a lack of data examining the effect that the microstructure plays in determining strength parameters.  This project aims to use a variety of existing high strain rate experimental equipment to examine the response of geological materials. Novel methodologies and diagnostics will need to be developed to monitor grain level behaviour and relate this to macroscale properties. Interaction with computational modelling will also be sought, to enhance the understanding of the experimental results obtained. The research group has substantial experience in this area and maintains a variety of relevant industrial contacts.

Granular materials under high rates of compaction (Dr C Braithwaite / Dr James Perry)

The processes by which brittle granular materials compact largely depend on their microstructure and the properties and interactions of the grains themselves. Predicting the dynamic response of these systems requires knowledge of how grain-scale phenomena manifest as macroscopic response. Such insight is crucial for a wide range of high rate applications including planetary formation and impact cratering, the response to blast and

penetration, and predicting and improving soil response to earthquakes and landslips through seismic coupling.  This project will follow on from a highly successful project studying the shock compaction of cohesionless sands at different moisture levels; it will extend the research programme to silts (smaller grain sizes), cohesive materials such as clays, and will begin to study how granular compaction can be controlled using suitable ‘modifiers’.

Ultra-fast temperature sensors for shock (Dr D Williamson)

Accurate temperature measurement during high speed events remains a consistent problem in shock-physics. Existing transducers are rate limited by their thermal mass, whereas standard optical techniques can only be applied under limited conditions (usually very high temperatures). In this project, we will focus on developing new techniques for ultra-fast temperature measurement. These will include modelling, fabrication and testing of nanometre-scale thermistor based instrumentation and fast response infra-red pyrometry. The techniques will be applied to study shock temperatures in polymeric and liquid systems, which are of increasing industrial importance.

Adhesion and damage in composites (Dr D Williamson)

Composite materials are of great importance in the everyday world.  Their fundamentally inhomogeneous nature means composites can exhibit complex forms of behaviour, relating to characteristics of the binder, filler and the nature of the interaction between them.  This project will focus on predicting the behaviour of composites using physically based models, supplemented by experimental data.  Low temperature thermo-physical measurements enable key model parameters to be populated.  Predictions may then be validated using other, mechanically based, measurements.  It will suit a keen experimentalist, and will likely involve extensive collaboration with other researchers.

Dynamic properties of fibre composites (Dr James Perry)

Composite materials (particularly Glass-fibre reinforced polymer, GFRP) can be stronger and lighter than steel, and resistant to corrosion. Fibreglass has been used for decades in everything from small watercraft and waterslides to traffic lights and surfboards, and more recently high-performance composites have started to replace metals in applications such as bicycles, commercial aircraft and wind turbines. Although their properties can be highly desirable, there are several challenges to working with composites. They are highly anisotropic, degrade via damage prior to failure, and are not so much materials as structures, which means their properties can depend strongly on the macroscopic size and shape of a sample.

High-performance applications often push materials towards their extremes, and so it is critically important that we can understand when, how and why materials fail. In the Fracture group we are particularly interested in the rate-dependence of material properties. Even when the quasi-static properties of composites are now quite well understood, understanding of their high-rate dynamic response remains much more limited. Currently, this leads to the need for extensive, expensive, large-scale testing of composite components. If we are to use composites more widely and more cost-effectively, we first need to be able to better predict their behaviour and so reduce the need for physical testing. All of this starts with small-scale lab experiments, to start to unpick the underlying physics both quantitatively and phenomenologically.

Your idea here (Dr D Williamson / Dr C Braithwaite / Dr James Perry)

We are always open to ideas with regards to potential PhD projects within the group's field of research, including joint and interdisciplinary projects run between several research groups, where students have access to funding (Departmental, College, JRF etc) - see our research and facilities pages if you need some inspiration.