My research group work on understanding the behaviour of materials under extreme environments, such as radiation damage, high temperatures or high stresses. By developing an understanding of the mechanical behaviour and defects which control materials behaviour we then try and develop materials better able to operate under extreme conditions. We are now working to take technqiues we have developed for traditional engineering materials and apply them to questions in other areas such as solid state batteries for energy storage and geological materials.
Much of our work is centred on developing mechanical testing techniques at the nano and micro scale. We have a state of the art high temperature nanoindentation system which allows us to perform tests up to temperature above 1000K. These techniques are being used to study a range of important materials for both nuclear power and aerospace applications. We also work with leading groups in Oxford and elsewhere to use understanding gained from our experiments to process new materials better suited to working under extreme conditions.
Materials systems being studied include; ceramic composites, high entropy alloys, refractory alloys, high strength steels and zirconium alloys. This is carried out with a range of partners including, UKAEA, General Atomics, Rolls Royce, Karlsruhe Institute of Technology, Germany and UC Berkeley, and University of Wisconsin-Maddison, USA, as well as many collaborators within Oxford. Particular areas of current research include:
Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine.
The strength of olivine at low temperatures and high stresses in Earth's lithospheric mantle exerts a critical control on many geodynamic processes, including lithospheric flexure and the formation of plate boundaries. Unfortunately, laboratory-derived values of the strength of olivine at lithospheric conditions are highly variable and significantly disagree with those inferred from geophysical observations. We demonstrate via nanoindentation that the strength of olivine depends on the length scale of deformation, with experiments on smaller volumes of material exhibiting larger yield stresses. This "size effect" resolves discrepancies among previous measurements of olivine strength using other techniques. It also corroborates the most recent flow law for olivine, which proposes a much weaker lithospheric mantle than previously estimated, thus bringing experimental measurements into closer alignment with geophysical constraints. Further implications include an increased difficulty of activating plasticity in cold, fine-grained shear zones and an impact on the evolution of fault surface roughness due to the size-dependent deformation of nanometer- to micrometer-sized asperities.