Analysis of bolted connection used in a reflectometry system for ITER Aerospace Engineering

113 Pages·2017·14.66 MB·English

by  Diogo Murteira

Analysis of bolted connection used in a reflectometry
system for ITER

Diogo Miguel dos Santos Mendes Vilar Murteira

Thesis to obtain Master of Science Degree in

Aerospace Engineering
Supervisors: Prof. Miguel António Lopes de Matos Neves
Dr. Hugo Filipe Diniz Policarpo

Examination Committee
Chairperson: Prof. Filipe Szolnoky Ramos Pinto Cunha
Supervisor: Prof. Miguel António Lopes de Matos Neves
Member of the Comittee: Prof. Eduardo Joaquim Anjos de Matos Almas

April 2017
Acknowledgments
I would like to express my thanks to:
My supervisor, Professor Miguel de Matos Neves, for his guidance, availability to help, for his
revision of this thesis and the support he gave me throughout its completion.
My co-supervisor, Doutor Hugo Policarpo, for his guidance, support and motivation, and for
always trying to be available to help.
Instituto de Plasmas e Fusão Nuclear as an institution, for the trust laid on me and for choosing
me to work in this project.
Engineering Systems and Integration team at Instituto de Plasmas e Fusão Nuclear, especially
to Paulo Quental, for all the help they managed to give me, even though they were not in any
obligated to do so.
Everyone that, in one way or another, participated in my path as a student.
My family, and my girlfriend, for the unconditional and untiring support provided to me.
The work leading to this publication has received financial support from Fundação para a Ciência
e Tecnologia (FCT) through project UID/FIS/50010/2013 through grant BL58/2016. Author further
acknowledge the data provided by Fusion for Energy under F4E-FPA-375-04.

i
Resumo
Este trabalho tem como objetivo a proposição e avaliação de uma metodologia para realizar
análises termo-estruturais de ligações aparafusadas de um sistema de refletometria para o ITER.
Os principais factores a ter em conta nas análises são o alinhamento das ligações, visto que
unem segmentos de guias de micro-ondas, e a comparação das distribuições de tensões obtidas
com os limites definidos pelo ITER.ddddddddddddddddddddddddddddddddddddddddd
As análises são realizadas no software de elementos finitos Ansys® Workbench Mechanical. Os
modelos de ligação analisados foram criados e adaptados especialmente para o efeito,
recorrendo ao desenho assistido por computador. Tanto as ferramentas de análise disponíveis
no software de elementos finitos, como as opções de modelação utilizadas na metodologia
proposta são descritas em pormenor. A metodologia proposta foi verificada, aplicando a mesma
a problemas cuja solução analítica é conhecida. Foi também aplicada para a análise de ligações
aparafusadas em três casos de carregamento distintos. Ligação sujeita apenas ao aperto dos
parafusos,ligação sujeita a aperto e distribuição de temperatura imposta e ligação sujeita a aperto
e um carregamento limite estático. Concluiu-se acerca das vantagens e limitações da
metodologia proposta: Permite extrair informação sobre tensões nos parafusos que pode ser
comparada com limites impostos pelo ITER, e sobre o alinhamento dos guias de onda. Apresenta
problemas no que toca à convergência de tensões em pontos de singularidade e em interfaces
de contacto.

Palavras-chave: ITER, refletometria, ligação aparafusada, elementos finitos, análise termo-
estrutural
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Abstract
The goal of this work was to propose and evaluate a methodology to perform thermal-structural
analysis in bolted connections of a reflectometry system for ITER. The main concerns the
analyses should cover are the connections’ alignment, given that they connect guides through
which microwave radiation travels. Also the comparison between stress distributions and stress
limits defined by ITER. The analyses were performed in Finite Element software Ansys
Workbench Mechanical. The connection models were specially created for this work using
computer-aided-design (CAD). Both the analysis tools provided by the software and the modelling
options used in the proposed methodology are described in detail. The methodology was verified
by applying it to solve problems for which analytical solutions are known. It was also applied to
the analysis of bolted connections under three distinct loading cases. Connection subject only to
bolt-tightening force, connection subject to bolt pre-tightening and imposed temperature
distribution, and connection subject to bolt pre-tightening and “worst-case-scenario” static
loading. Conclusions were drawn about the advantages and limitations of the proposed
methodology: It is able to provide converged results on bolt stress that can be compared to ITER
defined stress limits and to provide insight on waveguides alignment. It presents some problems
regarding stress convergence in singularity points and contact regions.

Keywords: ITER, reflectometry, bolted connection, finite element analysis, thermal-structural
analysis
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Contents
Figure Index .................................................................................................................................. vii
Table Index .................................................................................................................................... x
List of Symbols .............................................................................................................................. xi
List of abbreviations .................................................................................................................... xiv
1 Introduction ............................................................................................................................ 1
1.1 ITER .............................................................................................................................. 1
1.1.1 Project description ................................................................................................. 1
1.1.2 Reactor’s Components .......................................................................................... 1
1.2 PPR system ................................................................................................................... 2
1.2.1 Main concerns regarding bolted connections ........................................................ 2
1.3 Motivation ...................................................................................................................... 3
1.4 Aerospace Engineering framework ............................................................................... 3
2 Theoretical Background ........................................................................................................ 5
2.1 Solid Mechanics – Linear Elasticity ............................................................................... 5
2.1.1 Stress..................................................................................................................... 5
2.1.2 Cauchy’s Formula .................................................................................................. 5
2.1.3 Equations of Equilibrium ........................................................................................ 6
2.1.4 Strain ..................................................................................................................... 6
2.1.5 Small deformations ................................................................................................ 7
2.1.6 Hooke’s Law .......................................................................................................... 8
2.1.7 Principal Stresses and Principal Axes ................................................................... 8
2.1.8 Yielding Stress and Ultimate Tensile Strength ...................................................... 8
2.1.9 Von-Mises Stress and Failure Criterion ................................................................. 9
2.1.10 Simplifying Assumptions........................................................................................ 9
2.2 Thermoelasticity .......................................................................................................... 11
2.3 Bolted Connections ..................................................................................................... 11
2.3.1 Typical bolted joint [17] ........................................................................................ 11
2.3.2 Pretension ........................................................................................................... 12
2.3.3 Bolt Threads ........................................................................................................ 12
2.3.4 Fastener nomenclature........................................................................................ 12
2.3.5 Washers .............................................................................................................. 13
2.3.6 Fastener Stiffness ................................................................................................ 13
2.3.7 Member stiffness ................................................................................................. 13
2.3.8 Tension joints ...................................................................................................... 14
2.4 Finite Element Method (FEM) ..................................................................................... 15
2.4.1 Structural FEM ..................................................................................................... 16
2.5 ITER Structural Design Criteria ................................................................................... 19
3 Methodology ........................................................................................................................ 20
3.1 Verification of the procedure used in the software ...................................................... 20
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3.1.1 Thermal-structural verification ............................................................................. 20
3.1.2 Static Structural verification ................................................................................. 21
3.2 PPR system bolted connections analysis method ...................................................... 21
3.2.1 Examination of existing CAD models and selection of sub-assemblies of interest
22
3.2.2 Importation of geometries into AWB .................................................................... 22
3.2.3 Alteration of individual models ............................................................................. 23
3.2.4 Defeaturing .......................................................................................................... 24
3.2.5 Creation of FE model ........................................................................................... 24
3.3 Application of Analysis Method ................................................................................... 32
3.3.1 C1 with Pretension Only ...................................................................................... 32
3.3.2 C2 with Pretension and Temperature Distribution .............................................. 32
3.3.3 C1 and waveguides under Pretension and “Worst-case Scenario” Static Loading
32
4 Results and Discussion ....................................................................................................... 35
4.1 Plate with imposed temperature .................................................................................. 35
4.1.1 FEA in ANSYS Workbench ................................................................................. 35
4.2 Fastened concentric circular plates ............................................................................. 37
4.2.1 FEA of “fastened concentric plates” in AWB ....................................................... 37
4.3 C1 analysis with pretension only ................................................................................. 39
4.3.1 Material and Dimensions for “C1 analysis with pretension only”......................... 39
4.3.2 Mesh for “C1 analysis with pretension only”........................................................ 40
4.3.3 Boundary Conditions ........................................................................................... 40
4.3.4 Contacts for “C1 analysis with pretension only” .................................................. 41
4.3.5 Results of “C1 analysis with pretension only”...................................................... 42
4.4 C2 analysis with pretension + imposed temperature distribution ................................ 54
4.4.1 Material and Dimensions ..................................................................................... 54
4.4.2 Mesh .................................................................................................................... 54
4.4.3 Boundary Conditions ........................................................................................... 55
4.4.4 Contacts .............................................................................................................. 55
4.4.5 Number of Load Steps in Analysis ...................................................................... 55
4.4.6 Results ................................................................................................................. 55
4.5 Pretension and “Worst-case Scenario” Static Loading ............................................... 62
4.5.1 Material and Dimensions ..................................................................................... 62
4.5.2 Mesh .................................................................................................................... 62
4.5.3 Contacts .............................................................................................................. 63
4.5.4 Boundary Conditions and Loads ......................................................................... 63
4.5.5 Number of Steps in Analysis ............................................................................... 65
4.5.6 Results ................................................................................................................. 65
5 Conclusions ......................................................................................................................... 71
6 Future Work ......................................................................................................................... 71
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References .................................................................................................................................. 72
Appendix I – CAD models and Dimensions ................................................................................ 74
Appendix II – Materials ................................................................................................................ 78
Appendix IV – Meshing Parameters ............................................................................................ 80
Appendix V –Path Convergence Results .................................................................................... 85

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Figure Index
Fig. 1.1 – ITER components schematic [2] ................................................................................... 1
Fig. 1.2 – GAP 4’s PPR system portion with components highlighted in different colors ............. 2
Fig. 2.1 – Stress components on a infinitesimal cube [13] ............................................................ 5
Fig. 2.2 – Forces acting on faces of infinitesimal cube [13] .......................................................... 6
Fig. 2.3 – Deformation vectors [14] ............................................................................................... 7
Fig. 2.4 – Tensile test scheme [15] ............................................................................................... 8
Fig. 2.5 – Engineering Stress-Strain Curve at different stages of tensile test [16] ....................... 9
Fig. 2.6 – Typical Bolted Joint [17] .............................................................................................. 11
Fig. 2.7 – Triangular ISO Thread Profile [18] .............................................................................. 12
Fig. 2.8 – Pressure cone in bolted connection [18] ..................................................................... 13
Fig. 2.9 – Tension joint [18] ......................................................................................................... 14
Fig. 2.10 – Meshing of Trapezoid ............................................................................................... 15
Fig. 3.1 – CAD model of thin plate .............................................................................................. 20
Fig. 3.2 – AWB Project schematic – link between DM CAD model and MECH Static Structural
Analysis System .......................................................................................................................... 20
Fig. 3.3 – CAD model of Bolted connection ................................................................................ 21
Fig. 3.4 – Flange connection of type 1 (C1) without bolts .......................................................... 22
Fig. 3.5 – Bolted flange connection of type 2 (C2) without bolts ................................................. 22
Fig. 3.6 – Altered C1 CAD model including fasteners ................................................................. 23
Fig. 3.7 – New C2 CAD model including fasteners ..................................................................... 23
Fig. 3.8 – C1’s top flange: a) before defeaturing; b) after defeaturing) ....................................... 24
Fig. 3.9 – Link between Engineering Data and Static Structural Analysis System ..................... 24
Fig. 3.10 – Defining a Symmetry region ...................................................................................... 25
Fig. 3.11 – a) Path creation menu; b) Surface creation menu .................................................... 26
Fig. 3.12 – a) Highlighted contact between washer and flange; b) Contact definition menu ...... 27
Fig. 3.13 – Comparison between contact formulations [32] ........................................................ 28
Fig. 3.14 – Definition of “Bolt Thread Contact Geometry Correction” ......................................... 29
Fig. 3.15 – a) Mesh created by Multizone method; b) Skewness of elements .......................... 30
Fig. 3.16 – “Analysis Settings” menu........................................................................................... 31
Fig. 3.17 – a) Defining highlighted face “Element Size” as “Parameter”; b) Creating DPs 1,2 and
3, where “Element Size” is 2, 3 and 4 mm, respectively ............................................................. 32
Fig. 3.18 – Partial PPR system (control points 1-12 are indicated) ............................................ 33
Fig. 3.19 – Reduced model for Analysis ..................................................................................... 34
Fig. 3.20 – Simplified model with covers merged into a single parts and small features
eliminated .................................................................................................................................... 34
Fig. 4.1 – Results with BCs set 1 (mesh is visible) ..................................................................... 36
Fig. 4.2 – Results with BCs set 2 (mesh is visible) – normal stress y and z axis is -267.4 MPa 36
Fig. 4.3 – Mesh of bolted connection .......................................................................................... 37
Fig. 4.4 – Element Skewness of mesh from Fig. 4.3................................................................... 38
Fig. 4.5 – BCs in applied to analyzed bolted connection ............................................................ 38
Fig. 4.6 – Cross sectional and 3D views of normal (on the right-hand side) and VM (on the left-
hand side) stress ......................................................................................................................... 39
Fig. 4.7 – Mesh for C1 “Pretension Only” Analysis (with assembly parts identified) .................. 40
Fig. 4.8 -a) Element Skewness ; b) Element Quality................................................................... 40
Fig. 4.9 – BCs for analysis: A- Fixed support, C – Fixed x-direction motion, D – Fixed z-direction
motion .......................................................................................................................................... 41
Fig. 4.10 – “Frictionless” contact regions between: a) bolt and BF hole, b) bolt and TF hole, c)
bolt and washer ........................................................................................................................... 42
Fig. 4.11 – Total Displacement Distribution a)Solid view ; b) Cross-sectional view ................... 43
Fig. 4.12 – Paths for tracking displacement results .................................................................... 43
Fig. 4.13 – Separation zone in flanges (results magnification factor = 6.5×102) ........................ 44
Fig. 4.14 – VM Stress Distribution a) Solid isometric view; b) front cross-sectional view ........... 45
Fig. 4.15 – VM distribution in Bolt................................................................................................ 45
Fig. 4.16 – “Surfaces” created to evaluate mean and maximum stress intensities .................... 46
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Fig. 4.17 – VM Stress distribution in Nut ..................................................................................... 47
Fig. 4.18 – VM Stress distribution in Washer .............................................................................. 47
Fig. 4.19 – TF VM Stress Distribution ......................................................................................... 48
Fig. 4.20 – BF VM Stress Distribution ......................................................................................... 48
Fig. 4.21 – Convergence of maximum total deformation ............................................................ 49
Fig. 4.22 – Convergence of alignment results ............................................................................. 49
Fig. 4.23 – Cross-sectional view of VM Stress distribution for most refined mesh ..................... 50
Fig. 4.24 – Maximum stress in bolt for meshes 3 through 6 ....................................................... 50
Fig. 4.25 – Vertical “Paths” created to track VM Stress results .................................................. 51
Fig. 4.26 – “Paths” created to study VM stress convergence in nuts .......................................... 52
Fig. 4.27 – “Paths” created to study VM stress convergence in washer ..................................... 52
Fig. 4.28 – “Paths” created to study VM stress convergence in flanges ..................................... 53
Fig. 4.29 - Mesh used in “C2 with pretension and imposed Temperature distribution” analysis 54
Fig. 4.30 - a) Element Skewness ; b) Element Quality................................................................ 54
Fig. 4.31 – Imported body temperature ....................................................................................... 55
Fig. 4.32 – Displacement distribution for step 1 a) Solid view; b) Cross-sectional view ............. 56
Fig. 4.33 – Displacement distribution for step 3 a) Solid view; b) Cross-sectional view ............. 57
Fig. 4.34 – VM Stress Distribution a) Solid isometric view first; b) front cross-sectional view in
the bottom .................................................................................................................................... 58
Fig. 4.35 –“Surfaces” created to track stress intensity ................................................................ 58
Fig. 4.36 – Convergence plots for maximum total deformation in both load steps considered .. 60
Fig. 4.37 – Convergence plot of alignment study for load step 3 ................................................ 61
Fig. 4.38 – Mesh for Anlalysis of C1 with pretension + “worst-case-scenario” loading .............. 62
Fig. 4.39 – a) Element Skewness ; b) Element Quality ............................................................... 63
Fig. 4.40 – BCs for Analysis ........................................................................................................ 63
Fig. 4.41 – Displacement distribution for step 2: top – Solid view; bottom – Cross-sectional view
..................................................................................................................................................... 66
Fig. 4.42 – VM Stress Distribution: top - Solid isometric view; bottom - front cross-sectional view
..................................................................................................................................................... 67
Fig. 4.43 – VM Stress Distribution in flanges: step 2 in the left-hand side; step 1 in the right-
hand side ..................................................................................................................................... 68
Fig. 4.44 - Convergence plot of alignment study for last load step ............................................ 69
Fig. 4.45 – Path scheme for tracking stress results on flanges a) Top view; b) Front View ....... 70
Fig. 8.1 - Dimensions for bolted plates verification model .......................................................... 74
Fig. 8.2 - Dimension for flange of connection C1 - front cross-sectional view ............................ 74
Fig. 8.3 - Dimensions for flange of connection C1 - top view ...................................................... 75
Fig. 8.4 - Dimensions for flange of connection C1 - bottom view ................................................ 75
Fig. 8.5 - Dimensions for flange of connection C2- front cross-sectional view ........................... 75
Fig. 8.6 - Dimensions for flange of connection C2 top/bottom view ............................................ 76
Fig. 8.7 - Dimensions for fastener models used in C1 and C2 analysis ..................................... 76
Fig. 8.8- Dimensions for waveguides, cover and pads - top/bottom view (C1 under "worst-case-
scenario" loading) ........................................................................................................................ 76
Fig. 8.9 - Dimensions for waveguides, cover and pads - front cross-sectional (C1 under "worst-
case-scenario" loading) ............................................................................................................... 77
Fig. 8.10 -AWB's SOLID186 ........................................................................................................ 79
Fig. 8.11 - a) CONTA174; b) TARGE170 .................................................................................... 79
Fig. 8.12 - Bolt body sizing .......................................................................................................... 80
Fig. 8.13 - Circular edges sizing .................................................................................................. 80
Fig. 8.14 - Nut face meshing ....................................................................................................... 80
Fig. 8.15 - Washer face meshing ................................................................................................ 81
Fig. 8.16 - Washer face sizing ..................................................................................................... 81
Fig. 8.17 - Flanges edge sizing 1 ................................................................................................ 81
Fig. 8.18 - Flanges edge sizing 2 ................................................................................................ 81
Fig. 8.19 - Flanges edge sizing 3 ................................................................................................ 82
Fig. 8.20 – flanges edge sizing 4................................................................................................. 82
Fig. 8.21 – Circular edge sizing for “Pretension and imposed body temperature” analysis ....... 83
viii
Fig. 8.22 - edge sizing 1 for “Pretension and imposed body temperature” analysis ................... 83
Fig. 8.23 - edge sizing 2 for “Pretension and imposed body temperature” analysis ................... 83

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