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Edmund Tarleton

Dr Edmund Tarleton CEng, MIMMM
EPSRC Fellow in Dislocation Modelling

Department of Materials
University of Oxford
16 Parks Road
Oxford OX1 3PH
UK

Tel: +44 1865 273768 (Room 110.15.04)
Tel: +44 1865 273777 (reception)
Fax: +44 1865 273789 (general fax)

Micromechanics Group
MFFP Group

Summary of Interests

-Dislocation dynamics

-Finite element method

-Crystal plasticity

Current Research Projects

Dislocation based modelling of engineering alloys
Dr E. Tarleton, Dr H. Yu, B. Bromage, D. Garza, Professor. A.J. Wilkinson
If loaded a small amount, a metal will deform elastically, returning to its original shape when the load is removed. However if the load exceeds some value, then permanent deformation occurs, known as plasticity. Plasticity is far more complex to understand than elasticity as it involves breaking lines of atomic bonds in the metal. These lines of broken atomic bonds are called dislocations. In the last decade it has become possible to perform mechanical tests on samples that are only a few microns in size. The samples are so small, that by utilizing the power of modern graphics cards, it will be possible to simulate the experiment including every dislocation in the material explicitly, and watch how they interact with each other and with multiple precipitates. Being able to simulate an entire experiment at this level of detail is unprecedented and it will provide new insights into the details of what exactly goes on when metal deforms plastically and fractures.  The fundamental new insights gained during the project will be used to develop more accurate engineering design rules for industry. Funded by EPSRC.

Brittle-ductile transitions in BCC metals for fusion power applications
Dr D.E.J. Armstrong, Dr. E. Tarleton, Professor S.G. Roberts, Dr. A.J. Wilkinson, Professor S.L. Dudarev*
The project investigates the brittle-to-ductile transition in tungsten and iron-chromium alloys up to 12%Cr (all these metals are the basis for proposed fusion power plant alloys). Pre-cracked miniature bend specimens of single crystals and polycrystalline materials are fracture tested in the temperature range 77 - 450K. The effect of dislocation motion around the crack tips on fracture stress is examined, and modelled using dynamic-dislocation simulations. Funded by EPSRC and CCFE. (*EURATOM/CCFE)

2 public active projects

Research Publications

My recent publications are available here

 

 

 

Projects Available

Dislocation based modelling of engineering alloys
E Tarleton and Prof A J Wilkinson

You will be part of a small dynamic team developing state of the art computational models which are used to simulate a range of micro mechanical tests and microscopy data. This project focuses on simulating delayed hydride cracking in Zr alloys as used in compact nuclear reactors for submarine propulsion. You will simulate the coupled mechanical/hydrogen diffusion process within a discrete dislocation plasticity framework. This will involve developing a FEM code to solve the H diffusion equation, and coupling this with a discrete dislocation plasticity code to simulate dislocation-hydrogen interactions. The majority of the coding will be in Matlab, with the opportunity to learn and use C and CUDA to accelerate the code.

The project will link to experimental work within the wider Materials for Fusion and Fission Power group and may involve interaction with Rolls Royce (Marine).

 

Also see homepages: Edmund Tarleton Angus Wilkinson

Modeling of Micromechanical Testing of Irradiated Nuclear Fusion Materials
Edmund Tarleton, Angus Wilkinson, David Armstrong Oxford, Chris Hardie CCFE

Understanding how irradiation damage from neutrons affects the mechanical properties of structural materials is a key step towards realising nuclear fusion as a sustainable power source.  However working on irradiated materials is costly, and generating mechanical data from them is difficult. Neutron damage can be simulated with ion irradiations but the damage layers are thin -  200nm to 100µm. As such traditional mechanical testing methods cannot be used and novel micro-mechanical tests must be conducted. This leads to difficulties in interpreting the results due to size effects inherent in testing small material volumes.

This project will involve coding, debugging and performing simulations with state of the art computer models being developed in Oxford namely a coupled 3D (DDP) discrete dislocation plasticity / finite element code and a crystal plasticity finite element code (Abaqus UMAT) to simulate nano-indentation experiments. The experiments you will simulate are being performed at the Materials Research Facility at the Culham Centre for Fusion Energy to study the effects of ion irradiation on fusion materials and correlate this with the defect populations produced. The insight gained will then be used to develop methods to use small scale mechanical tests to aid engineering design of future fusion systems. Materials of interest include chromium, vanadium and tungsten based alloys.

 

Key challenges will be how to accelerate the code using a GPU, how to implement the correct traction/displacement boundary conditions, and how to incorporate complex geometry such as multiple precipitates. You will be part of a small team developing the codes and performing simulations and will also interact closely with experimental researchers at MRF at CCFE as well as work in the Oxford Materials Department and therefore will have access to rich data sets to validate and improve the model. The ultimate goal of the project is to be able to perform virtual experiments that reproduce real experiments and in doing so fully understand the mechanisms which control deformation of irradiated materials.

Also see homepages: David Armstrong Edmund Tarleton

Understanding High Temperature Small Scale Mechanical Performance of Materials for Nuclear Fusion
Dr D.E.J. Armstrong, Dr E. Tarleton, Professor A.J. Wilkinson,

Future nuclear power systems, both fission and fusion, rely on the development of materials which can withstand some of the most extreme engineering environments. These include temperatures up to 1500oC, high fluxes of high energy neutrons and effects of gaseous elements produced by transmutation and implantation from the plasmas. Due to efforts to minimise the production of nuclear waste by such reactors the elements which may be used in structural components is limited and in many cases there is a lack of understanding of the basic deformation processes occur in ether pure materials or alloys and importantly how these are affected by temperature, radiation damage and gas content. This project will build upon the expertise in the MFFP and Micromechanics groups on high temperature mechanical testing at the micro and nano-scale. Facilities include two high temperature nanoindenters (-50oC to 950oC), high temperature microhardness (RT to 1500oC) and dedicated FIB-SEM and FEG-SEM with EBSD as well as state of the art computer codes for strain gradient crystal plasticity finite element modelling and discrete dislocation plasticity modelling. Both nanoindentation, micro-compression and micro-bend experiments will be used to study plastic deformation, fracture and creep in a range of novel high temperature materials (likely Fe, SiC or Zr based) with potential for use in future fusion reactors. HR-EBSD and AFM will be used to study deformation structures produced during testing and to inform strain gradient crystal plasticity finite element and discrete dislocation models. This will allow for a fuller understanding of the underlying physics of deformation in these materials both before and after irradiation or gas implantation. Strong links will be made to activities within the Science and Technology of Fusion Energy (EPSRC Centre for Doctoral Training) and the Culham Centre for Fusion Energy.

Also see homepages: David Armstrong Edmund Tarleton Angus Wilkinson

Micromechanical Testing of Irradiated Nuclear Fusion Materials
Dr David Armstrong, Dr Angus Wilkinson, Dr Edmund Tarleton, Oxford, Chris Hardie CCFE

Understanding how irradiation damage from neutrons affects the mechanical properties of structural materials is a key step towards realising nuclear fusion as a sustainable power source.  However working on irradiated materials is costly, and generating mechanical data from them is difficult. Neutron damage can be simulated with ion irradiations but the damage layers are thin -  200nm to 100µm. As such traditional mechanical testing methods cannot be used and novel micro-mechanical tests must be conducted. This leads to difficulties in interpreting the results due to size effects inherent in testing small material volumes.

This project will utilise the newly opened Materials Research Facility at the Culham Centre for Fusion Energy to study the effects of ion irradiation on fusion materials and correlate this with the defect populations produced. This will then be used to develop methods to use small scale mechanical tests to aid engineering design of future fusion systems. Materials of interest include chromium, vanadium and tungsten based alloys.

 

Ion irradiations will be carried out using protons and heavy ions at a range of international irradiation facilities, at fusion reactor relevant doses and temperatures. Advanced electron microscopy at the Department of Materials, University of Oxford will be used to characterise the damage and defect types produced. Micromechanical tests will be performed at the MRF to understand how these defects affect mechanical behaviour, such as fracture toughness, work hardening, and flow localisation. Tests conducted will include nano-indentation, micro-cantilever and compression tests and micro-scale tensile tests. Finite element modelling will be used to interpret the results. This work will be in close collaboration with a defect based modelling phd based at Oxford Materials, to fully understand the mechanisms which control deformation of irradiated materials. The student will be enrolled on the Fusion CDT and the project will involve significant periods of experimental work at the MRF at CCFE as well as work in the Oxford Materials Department.

Also see homepages: Edmund Tarleton

Strains Induced by Hydride Formation in Zirconium
Prof Angus J Wilkinson, Dr Ed Tarleton, and Dr David E J Armstrong

In service temperature cycling of nuclear fuel cladding can lead to repeated sequences of precipitation and dissolution of hydrides in zirconium based alloys. During the transformation from hydrogen in solid solution to the hydride phase there is a considerable volume expansion. This project will explore the links between nucleation sites, hysteresis between temperatures for precipitation and dissolution, the stress field and local plasticity induced by the transformation strain and the precipitation morphology. The following techniques will be used: high resolution EBSD, digital image correlation of SEM images, in situ thermal cycling, finite element based-crystal plasticity simulations. This project will be carried out in close conjunction with Rolls Royce and other partner Universities within the HexMat flagship EPSRC programme (http://www3.imperial.ac.uk/hexmat).

Also see homepages: David Armstrong Edmund Tarleton Angus Wilkinson

Also see a full listing of New projects available within the Department of Materials.