Supervisor: James Marrow (University of Oxford)
The safety and economic operation of future fusion systems will depend on their tolerance to damage by processes such as fatigue and fracture, These properties of structural materials are usually measured using standard test specimens. However, real cracks are three-dimensional and more complex, with strong influences from the microstructure that can be affected by temperature and irradiation. Predicting whether and how quickly a crack will propagate with confidence and without excessive conservatism remains difficult. We aim to improve our understanding of crack propagation by investigating how the applied loading is mediated by the processes that occur around the crack. In other words, what are the local conditions that exist at the crack tip that allow it to propagate. These can be quite different from what we might expect if we only consider the remotely applied boundary conditions, which are the loads or displacements and crack geometry (length and shape). This is important both for the fundamental investigation of material properties, but also for the qualification testing of new materials for engineering design that may require small-specimen testing or studies at the microscale.
One way to address this is to simultaneously examine both the strain and stress fields that exist when the crack propagates. This can be done by 2D and 3D digital correlation image analysis to obtain precise, in-situ, measurements of the material displacements at the surface and inside solid samples, and also measurements of the deformations of the crystal lattice by scattering of X-rays, neutrons or electrons. These measurements are used with numerical modelling to investigate the criteria for crack propagation. Some recent examples include fatigue cracks in metals (doi.org/10.1016/j.ijfatigue.2020.105474 and doi.org/10.1016/j.prostr.2022.03.139), cleavage cracks in ceramics (doi.org/10.1016/j.jmps.2022.105173) and nuclear graphite (doi.org/10.1016/j.carbon.2020.09.072 and doi.org/10.1007/s11340-021-00754-1).
The objective of this project is to develop novel methods to better characterise and understand the interaction between events at the crack tip and the surrounding deformation fields in materials (metals or ceramics) for fusion energy that are susceptible to degradation by fatigue, brittle fracture or stress corrosion. The project will use experimental techniques that include SEM, XRD (synchrotron), Raman, optical and X-ray tomography and finite element modelling.
The project is suitable for graduates with an engineering, mathematical or physics background.
The project will be mainly based in Oxford, but there is the opportunity for travel to conferences and experiments at national facilities.
This project is offered by University of Oxford. For further information please contact: James Marrow (james.marrow@materials.ox.ac.uk)
This project may be compatible with part time study, please contact the project supervisors if you are interested in exploring this.