The Size Effect: Theory and Experiment

Research Group: 
Centre for Condensed Matter and Material Physics
Length of Study in Years: 
Full-time Project: 
QM Scholarship
Project Description: 
The project will be part of an on-going experimental and theoretical research programme, including micromechanical experimentation and theoretical work on dislocation behaviour in confinement and on local and non-local theories of plasticity. The aim of the project is to develop a consistent and coherent understanding of the size effect (smaller is stronger; i.e. the effect of length scales on strength) in its many manifestations, supported by experimental studies. This will enable length-scale engineering in the design and fabrication of new or improved materials.

Specific experiments that would form the basis of the PhD programme could include nanoindentation, torsion of hollow wires (thin tubes) or bending of hollow thin foil structures. The student could undertake experiments on the torsion of very long thin wires in The Monument, London. Analysis and interpretation of new and existing data is an important part. Theoretical work would include interpretation of data in terms of critical thickness theory, and in terms of strain-gradient theory. The student could also undertake work aimed at the reconciliation of these two very different theoretical approaches.

The students will undergo training in the area of micromechanical experimentation, metallurgy, statistical analysis, fundamental physics of materials science.

Recent references:
Y. Li, A.J. Bushby and D.J. Dunstan, 2016, The Hall-Petch effect as a manifestation of the general size effect, Proc Roy Soc A 472, 20150890.
D. Dong, D.J. Dunstan and A.J. Bushby, 2015, Plasticity and thermal recovery of thin copper wires in torsion, Phil Mag 95, 1739-1750.
An interest in the strength of materials
A good first degree in Physics, Engineering or Materials Science
SPA Academics: 
David Dunstan