PhD studentships
The Mechanical Properties of Nanowires
It is well known that the yield strength of polycrystalline materials decreases with decreasing grain size and this is well described by the Hall-Petch relation. It is also well documented that as small volumes of material are tested there is also an increase in the measured yield stress. In many of these small volume tests, e.g. nanoindentation or the torsion of small wires with radii < 10 microns, the increase in yield stress is ascribed to "strain gradient plasticity" or the presence of "geometrically necessary dislocations". Recent experiments have tested single crystal metal nanowires with diameters in the range 100 - 500 nm in compression to find an increase in yield stress in the absence of strain gradients; there have also been reports on the deformation of nanowires in bending that report much higher yield strengths. In this project we will investigate differences in the deformation of nanowires when tested in compression and by bending. Deformation of very small volumes of material can act as a test for geometric aspects of deformation and probe the role of strain gradients in enhancing yield stress.
Single crystal metallic nanowires will be grown using nanoporous alumina templates using procedures developed in recent years in Manchester. Deformation experiments will be carried out in compression using a nanoindenter as an ultra-low load testing system. Nanowire bending will be carried out using AFM loading of nanowire samples fixed in position by focussed ion beam methods. Simple dislocation models will be used to determine the density of geometrically necessary dislocations that must be generated to accommodate observed bending deformation and these used to calculate enhanced bending stresses using virtual work models. We will also develop a continuum plasticity model of bending using strain gradient plasticity to test whether empirical continuum plasticity models operate at this length scale.
The student will also carry out transmission electron microscopy of deformed nanowires to verify the presence of geometrically necessary dislocations.
Degree Type
3 year PhD
Eligibility
Good Honours Degree (2:1 or better) in Materials Science, Physics, Engineering or related discipline
Funding
If you are from UK / EU you can apply for funding for this studentship through the School's EPSRC Doctoral Training Account (DTA). The award will provide Home tuition fees and an EPSRC-level stipend of £12,600.
Awards will be based on the merit of your application against the applications of other applicants. There is no deadline for applications, but the majority of funding will be allocated in June 08.
Start Date
September 2008
Application Deadline
Available until filled
Reference
PhD/07/BD/04
Supervisor Contact Details
For further information about the project, please contact:
Email: Brian.Derby@manchester.ac.uk
Tel: +44 (0)161 306 3569
Admissions Contact
Postgraduate Team, School of Materials
Email: pg-materials@manchester.ac.uk
Tel: +44 (0)161 306 4824
How to Apply
You can apply for postgraduate opportunities online quoting the project reference number.