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Finite Element Modelling of Friction Stir Welding on Copper Canister
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.ORCID iD: 0000-0002-8494-3983
2004 (English)In: 5th International Friction Stir Welding symposium, 2004Conference paper, Published paper (Refereed)
Abstract [en]

In an effort to enhance safety for long time deposit of waste nuclear fuel, friction stir welding has been tentatively used to seal copper canisters. To avoid the formation of voids and cracks during the welding process, and to understand the heat and material flow as well as the evolution of the microstructure, are of great importance. Finite element modelling has been used to simulate the friction stir welding process.

A model involving heat transfer, material flow, and continuum mechanics has been developed. The steady state solutions have been compared with experimental temperature observations as well as analytical solutions, showing good agreement. Temperature distribution is affected by the welding speed. For a given reference point perpendicular to the welding direction, a lower welding speed corresponds to a higher peak temperature. The plunging position of welding tool influences the temperature distribution and therefore also the thermal distortion of the weldment.

Place, publisher, year, edition, pages
2004.
Keyword [en]
friction stir welding, FSW, copper, finite element modelling
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-12012OAI: oai:DiVA.org:kth-12012DiVA: diva2:294093
Conference
5th International Friction Stir Welding symposium, Metz, France, 14-16 September, 2004
Note
QC 20100719Available from: 2010-02-16 Created: 2010-02-16 Last updated: 2010-12-07Bibliographically approved
In thesis
1. Investigation and modelling of friction stir welded copper canisters
Open this publication in new window or tab >>Investigation and modelling of friction stir welded copper canisters
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work has been focused on characterisation of FSW joints, and modelling of the process, both analytically and numerically. The Swedish model for final deposit of nuclear fuel waste is based on copper canisters as a corrosion barrier with an inner pressure holding insert of cast iron. Friction Stir Welding (FSW) is the method to seal the copper canister, a technique invented by The Welding Institute (TWI).

The first simulations were based on Rosenthal’s analytical medium plate model. The model is simple to use, but has limitations. Finite element models (FEM) were developed, initially with a two-dimensional geometry. Due to the requirements of describing both the heat flow and the tool movement, three-dimensional models were developed. These models take into account heat transfer, material flow, and continuum mechanics. The geometries of the models are based on the simulation experiments carried out at TWI and at Swedish Nuclear Fuel Waste and Management Co (SKB). Temperature distribution, material flow and their effects on the thermal expansion were predicted for a full-scale canister and lid. The steady state solutions have been compared with temperature measurements, showing good agreement.

In order to understand the material flow during welding a marker technique is used, which involves inserting dissimilar material into the weld zone before joining. Different materials are tested showing that brass rods are the most suitable material in these welds. After welding, the weld line is sliced, etched and examined by optical microscope. To understand the material flow further, and in the future predict the flow, a FEM is developed. This model and the etched samples are compared showing similar features. Furthermore, by using this model the area that is recrystallised can be predicted. The predicted area and the grain size and hardness profile agree well.

Microstructure and hardness profiles have been investigated by optical microscopy, Scanning Electron Microscopy (SEM), Electron Back Scatter Diffraction (EBSD) and Rockwell hardness measurements. EBSD visualisation has been used to determine the grain size distribution and the appearance of twins and misorientation within grains. The orientation maps show a fine uniform equiaxed grain structure. The root of the weld exhibits the smallest grains and many annealing twins. The appearance of the nugget and the grain size depends on the position of the weld. A large difference can be seen both in hardness and grain size between the start of the weld and when the steady state is reached.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. 62 p.
Keyword
Friction Stir Welding (FSW), Copper, Welding, Finite Element Method (FEM), SKB, Material flow
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-11999 (URN)978-91-7415-568-6 (ISBN)
Public defence
2010-03-04, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC20100719Available from: 2010-02-15 Created: 2010-02-12 Last updated: 2010-07-19Bibliographically approved
2. Friction stir welding of copper canisters for nuclear waste
Open this publication in new window or tab >>Friction stir welding of copper canisters for nuclear waste
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The Swedish model for final disposal of nuclear fuel waste is based on copper canisters as a corrosion barrier with an inner pressure holding insert of cast iron. One of the methods to seal the copper canister is to use the Friction Stir Welding (FSW), a method invented by The Welding Institute (TWI).

This work has been focused on characterisation of the FSW joints, and modelling of the process, both analytically and numerically. The first simulations were based on Rosenthal’s analytical medium plate model. The model is simple to use, but has limitations. Finite element models were developed, initially with a two-dimensional geometry. Due to the requirements of describing both the heat flow and the tool movement, three-dimensional models were developed. These models take into account heat transfer, material flow, and continuum mechanics. The geometries of the models are based on the simulation experiments carried out at TWI and at Swedish Nuclear Fuel Waste and Management Co (SKB). Temperature distribution, material flow and their effects on the thermal expansion were predicted for a full-scale canister and lid. The steady state solutions have been compared with temperature measurements, showing good agreement.

Microstructure and hardness profiles have been investigated by optical microscope, Scanning Electron Microscope (SEM), Electron Back Scatter Diffraction (EBSD) and Rockwell hardness measurements. EBSD visualisation has been used to determine the grain size distribution and the appearance of twins and misorientation within grains. The orientation maps show a fine uniform equiaxed grain structure. The root of the weld exhibits the smallest grains and many annealing twins. This may be due to deformation after recrystallisation. The appearance of the nugget and the grain size depends on the position of the weld. A large difference can be seen both in hardness and grain size between the start of the weld and when the steady state is reached.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 39 p.
Keyword
Materials science, Friction Stir Welding (FSW), Copper, Welding, Finite Element Method (FEM), Materialvetenskap
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-318 (URN)91-7283-974-0 (ISBN)
Supervisors
Note
QC 20101207Available from: 2005-07-19 Created: 2005-07-19 Last updated: 2010-12-07Bibliographically approved

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