dnv platform of computational welding mechanics1085879/fulltext01.pdf · dnv materials laboratory...

IIW 66th Annual Assembly 2013

September 11- 17, 2013

Essen, Germany

IIW Document Number: X-1732-13

Delegation of Norway and Sweden

Commission X

DNV Platform of Computational Welding Mechanics

Per R. M. Lindström

DNV Materials Laboratory, Det Norske Veritas AS, Høvik, Norway /

Department of Engineering Science, University West, Trollhättan, Sweden

ABSTRACT

This document presents the DNV Platform of Computational Welding Mechanics, CWM, with its

associated CWM-methodology. That has been developed, validated and implemented as a part of

DNV’s Technology Leadership program in the field of Structural Integrity and Materials Technology.

A successful CWM implementation requires that the actual organisation has gained the knowledge and

understanding of the following related topics:

- Welding Engineering with an emphasis on the welding process and its thermodynamics

- Weld process quality control such as calibration, validation as well as DAQ, (Data Acquisition)

- Transient thermo-mechanical coupled FE-analyses and constitutive modelling

- Computational platforms comprising the selection of hardware, operative system and FEM-code

as well as suitable pre- and post-processing tools

From that perspective there is a lack of reliable and/or hands-on oriented CWM Engineering

Handbooks and best recommended practices available on the market. For that sake is the DNV CWM-

methodology and its hands on solutions presented.

The CWM-methodology described can not only be used for residual stress assessments, as presented

in this report. It can also be used for various applications such as assessment of used and/or proposed

WPS, Welding Procedure Specifications as well as optimisation of the manufacturing and production

process of integrated metallic structures.

From the results of a parametric CWM-study have three (3) factors been identified to drive and/or

contribute to the magnitude of the weld residual stresses in ship steel plate materials. The contributing

and/or driving factors identified are the:

- Thermal- and Mechanical Boundary Conditions during the production welding

- Yield stress difference between the base- and the weld filler material - Weld heat input, Q, which affects the weld cooling time

IIW Keywords: Weld Residual Stresses, CWM, Computational Welding Mechanics, Weld Simulations, Kinematic Hardening, WPS Assessment, Distortion

DNV REPORT No.: 2014-3256

IIW 66th Annual Assembly 2013 i


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Table of Contents Page

1 INTRODUCTION ............................................................................................................................... 1

2 DNV CWM PLATFORM ................................................................................................................... 2 2.1 Introduction ...................................................................................................................... 2 2.2 HPC Linux Workstation ................................................................................................... 2

2.3 FEM-Solver at CWM-Simulations ................................................................................... 2 2.4 Pre- and Post-Processing .................................................................................................. 3 2.5 CWM Analysts ................................................................................................................. 4

3 DNV CWM MATERIAL MODEL .................................................................................................... 4 3.1 Use of the CWM-material models .................................................................................... 4

3.2 Thermal CWM-material model ........................................................................................ 5 3.3 Mechanical CWM-material model ................................................................................... 5

3.3.1 Residual Stress Releasing Function .................................................................................. 7

3.3.2 Residual Stress Release Temperatures ............................................................................. 7 3.3.3 Hardening Formulation ..................................................................................................... 8 3.3.4 Weld filler material activation .......................................................................................... 8

4 DNV CWM METHODOLOGY ......................................................................................................... 9 4.1 Introduction ...................................................................................................................... 9 4.2 Scrutinizing WPQR and WPS ........................................................................................ 10

4.3 Test Welding and DAQ .................................................................................................. 10 4.4 Weld Heat Calculations .................................................................................................. 10

4.4.1 3D Transient FE-Weld Simulations ............................................................................... 11

4.4.2 2D Transient FE-Weld Simulations ............................................................................... 12 4.5 2D Transient Thermo-Mechanical FEA ......................................................................... 19

4.6 Elastic Shakedown Analyses .......................................................................................... 20

5 CWM-STUDY OF RESIDUAL STRESS CONTRIBUTING FACTORS ...................................... 21

5.1 Introduction .................................................................................................................... 21 5.2 Assessment of the WPS .................................................................................................. 22

5.2.1 Weld Joint Geometry and CWM-Models ....................................................................... 22

5.2.2 Weld Heat Input .............................................................................................................. 25 5.2.3 Thermal and Mechanical Boundary Conditions ............................................................. 28

5.2.4 Elastic Shakedown Analyses .......................................................................................... 31 5.3 Description of the CWM Analyses Carried Out ............................................................. 32

5.3.1 Material properties and modelling .................................................................................. 33

5.4 Weld Residual Stress Results - Elastic Shakedown ....................................................... 34 5.4.1 Weld Residual Stress Results – Alternative 1 and Qmin ................................................. 35 5.4.2 Weld Residual Stress Results – Alternative 1 and Qnom ................................................. 36 5.4.3 Weld Residual Stress Results – Alternative 1 and Qmax ................................................. 37 5.4.4 Weld Residual Stress Results – Alternative 2 and Qmin ................................................. 38

5.4.5 Weld Residual Stress Results – Alternative 2 and Qnom ................................................. 39 5.4.6 Weld Residual Stress Results – Alternative 2 and Qmax ................................................. 40

5.4.7 Weld Residual Stress Results – Alternative 3 and Qmin ................................................. 41 5.4.8 Weld Residual Stress Results – Alternative 3 and Qnom ................................................. 42 5.4.9 Weld Residual Stress Results – Alternative 3 and Qmax ................................................. 43

6 DISCUSSION ................................................................................................................................... 44 6.1 Thermo- and Mechanical Boundary Conditions ............................................................ 44 6.2 Weld Heat Input .............................................................................................................. 45 6.3 Yield Stress Difference ................................................................................................... 46

IIW 66th Annual Assembly 2013 ii


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7 CONLUSIONS .................................................................................................................................. 47

8 REFERENCES .................................................................................................................................. 48

APPENDIX A Material Certificate NV Grade EH32

APPENDIX B Material & Physical Data


IIW 66th Annual Assembly 2013 1


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1 INTRODUCTION

This document presents the DNV Platform of Computational Welding Mechanics, CWM, with

its associated CWM-methodology. That has been developed, validated and implemented as a

part of DNV’s Technology Leadership program in the field of Structural Integrity and Materials

Technology.

In a scientific context FE-based, thermo-mechanical simulations to determine the temperature

and stress fields present during welding have been performed for about forty years. The FE-

technology and the computer capacity (computations and storage) have developed to a state that

Computational Welding Mechanics, CWM, is an established and mature process. ‎/1/ ‎/2/ It

implies that CWM can be used as a fairly reliable tool at the assessment of Welding Procedure

Specifications, WPS, and proposed weld process parameters. ‎/3/ ‎/4/ As well as parametric

studies for the sake of optimised weld residual stress fields at the structural integrity design

phase. ‎/5/ ‎/6/ ‎/7/ A number of FEM-weld simulation reports with experimental

verification ‎/8/ ‎/9/ ‎/10/ ‎/11/ and one (1) residual stress weld experiment ‎/12/ has recently been

presented. Areas where improvement may still be needed are:

- Data Acquisitioning, DAQ, of weld process parameters used and Quality Control, QC, of

the thermal- and mechanical boundary conditions affecting the actual weld test coupons to

be used for the purpose of CWM-calibration, -verification and/or -validation.

- Accurate modelling of the actual weld process parameters used or to be used

- Accurate modelling of the actual thermal- and mechanical boundary conditions used or to

be used

- Material modelling in particular at high temperatures and at solid state phase

transformations

- Geometric modelling and mesh density optimisation of complex weld joint configurations

- Modelling and/or definition of the transient thermal- and dynamic mechanical contact

problems associated with welding processes

A successful industrial CWM implementation requires that the actual organisation has gained the

knowledge and understanding of the following related topics:

- Computational platforms that comprises the selection of hardware, operative system and

FEM-code as well as suitable pre- and post-processing tools ‎/13/

- Welding Engineering with an emphasis on the weld process parameters and its

thermodynamics ‎/14/

- Quality Control, QC, of weld process related activities ‎/15/

- Transient thermo-mechanical coupled FE-analyses and constitutive modelling ‎/16/

Anyhow there is a lack of reliable and/or hands-on oriented CWM Engineering Handbooks and

best recommended practices available on the market creating a barrier that is preventing

engineers to gain understanding and knowledge in the topic. This has resulted in an extensive

and expensive learning curve for any individual that wants to gain the knowledge and skill of

CWM-analyses.

The methodology here presented has been validated against scientifically published benchmark

examples presented by IIW, International Institute of Welding ‎/17/ ‎/18/ as well as two (2)

commercial available CWM-codes. ‎/19/ ‎/20/




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2 DNV CWM PLATFORM

2.1 Introduction

This chapter describes various practical and theoretical aspects to be considered in conjunction

with CWM, Computational Welding Mechanics.

2.2 HPC Linux Workstation

Before an engineering organisation starts with CWM-activities one has to select and configure a

computational platform that will works in the industrial reality. DNV Materials Laboratory has

selected to use a 12 Core Fujitsu Celsius R670 HPC Work Station with dual boot of the operative

systems Microsoft Windows 7 and Linux CentOS-6.4 with a ThinLinc Desktop terminal server

as its default CWM computational platform. ‎/21/ ‎/22/ ‎/23/

2.3 FEM-Solver at CWM-Simulations

DNV Materials Laboratory has selected to use the commercial FEM-software LS-Dyna as its

default non-linear FEA-code for CWM-simulations. ‎/24/ ‎/25/ A disadvantage with the solver

selected compared to the FEA-solver ABAQUS is the lack of a comprehensive user manual.

ABAQUS is for the time being the “DNV in-house code for non-linear FE-simulations” that had

to be abounded at CWM-simulation due to lack of numerical performances. The computational

time for a 3D transient thermal TIG-bead on plate simulation was found to be about 6 – 8 times

longer by the use ABAQUS compared to LS-Dyna. ‎/26/ Anyhow in-depth descriptions of the

nonlinear finite element analysis methodologies used by the code, such as Lagrangian, Eularian

and arbitrary Lagrangian Eulerian are well and extensively described in the book “Nonlinear

Finite Elements for Continua and Structures”. ‎/27/ As well as the theoretical foundations of the

inelastic material modelling with its numerical formulation and implementation are described in

the book ”Computational Inelasticity. ‎/28/ Whilst the mathematically modelling of macroscopic

volume elements behaviour and the physics underlying the phenomena is presented in the book

”Mechanics of Solid Materials”. ‎/29/ The general LS-Dyna keyword users manuals, 2 volumes,

can be downloaded free of charge from the website of LSTC. ‎/30/

LS-Dyna is by default incorporating a “double ellipsoidal weld heat source”, commonly denoted

the Goldak heat source after its formulator. ‎/31/ The LS-Dyna version of the “Goldak double

ellipsoidal weld heat source” can be used for thermo-mechanical staggered coupled simulations

as well as thermal analyses only. The thermo-mechanical staggered coupled approach has been

found beneficial as the control of the 3D-movements is handled as a mechanical problem and

subsequently solved by the mechanical solver free from influences of the thermal solver and vice

versa. The general principles of heat conduction in solids and boundary layer theory as well as its

applications are described in ‎/32/ ‎/33/ ‎/34/.

A novel feature of the LS-Dyna’s Goldak heat source implementation, from a welding

engineering perspective, is that it is possible to orient the weld torch or electrode in any direction

and model the arc pressure weld pool surface depression. This makes it possible to include the

torch angle value stated in the WPS for the production of a specific weld joint as well as the arc

pressures of various weld processes, ‎Fig. 1. The first use of LS-Dyna’s Goldak weld heat source

adjustable parameters was presented 2012 ‎/16/ ‎/3/ and has been adopted here as well.




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Fig. 1. Illustration of how the heat flux emission can be controlled by the use of LS-Dyna’s Goldak weld heat source implementation, the green colour half spheres are symbolising the weld heat flux field volume.

2.4 Pre- and Post-Processing

CWM-analyses should be done by the use of a mapped Quad-/Hex mesh with transition elements

in order to facilitate robustness toward to excessive element deformations, Fig. 2.

Fig. 2. Illustration of a mapped Hexagonal CWM-mesh with transition elements

General pre- and post-processing is done by the use of LS-PrePost from LSTC in combination

with a suitable open source text editor such as Notepad++, NEdit or Vim. /35/ /36/ /37/ /38/ The

book “LS-DYNA for Beginners” is a useful step by step self-study book for the learning of LS-

PrePost and LS-Dyna. /39/ The pre-processor TrueGrid is recommended to be used at parametric

studies of weld joint geometry influences etc. /40/

At demanding modelling activities is the reading of the extensive amount of user manual pdf-

documents facilitated by the use of an “E-reader” such as Kindle or Letto. /41/ /42/




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2.5 CWM Analysts

Even if the FE-technology and the computer capacity (computations and storage) have

developed to a state that Computational Welding Mechanics, CWM, is an established and mature

process in a scientific context. It is far from that case in an industrial context that not is defence

and/or nuclear related. Resulting in a great need of CWM Handbooks targeting practicing

welding-, material-, and mechanical engineers as well as metallurgists with a M.Sc. degree or

similar. As existing CWM-books more or less are focusing on the scientific- and/or advanced

readers. /1/ /2/

One other obstacle that has to be overcome is the recruitment and training of CWM-analysts.

During the implementation of DNV’s CWM-Methodology has two (2) fairly new examined

engineers with a M.Sc. mechanics degree been given basic CWM-training. Based on the

experiences gained it has been concluded that the “On the job” training time required should be

about 6 weeks (enhanced with literature home studies when necessary). Preferable combined

with some sort of formal welding technology education of about 6 weeks. Such as IWS-

Diploma, International Welding Specialist and/or IWSD-Diploma, International Welded

Structures Designer. /43/

Anyhow the most fundamental knowledge a CWM-analyst must gain before he or she can start

to do FE-weld simulations is the reading, interpretation and understanding of the most basic

welding engineering documents such as WPQR and WPS. /2/ /4/ /44/ /45/ /46/ /47/ For that sake

it is highly recommended that a CWM-analyst has the access to some basic welding engineering

related handbooks. /48/ /49/ /50/ /51/

3 DNV CWM MATERIAL MODEL

In order to utilise the full potential of the LS-Dyna solver for the sake of CWM has DNV

Materials Laboratory developed a CWM-material model package that now is implemented into

the LS-Dyna solver package. /52/ /53/ The CWM-material model package is intentionally

compiled for the Implicit Double Precision MPP Solver of LS-Dyna and consists of two (2)

distinctively separated material models specifically:

- A thermal CWM-material model ‎/52/

- A mechanical CWM-material model ‎/53/

3.1 Use of the CWM-material models

At simulation of a multi pass weld joint is the CWM-material model used for:

- Base material

- Existing and solidified weld filler material

- Weld passes to be produced

The material activation temperatures, liquidus- and solidus temperature, are set to very low

values for the base material and existing weld passes, typical values used are:

- Liquidus temperature = 10-5

°C

- Solidus temperature = 10-6

°C

These setting results in that accumulated weld residual stresses in the base- and existing weld

filler material will be released if the temperature pass through the residual stress release

temperature interval (lower and upper residual stress release threshold).




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3.2 Thermal CWM-material model

The user-defined features of the thermal CWM-material model include:

- Weld filler material activation at a temperature interval defined by the analyst

- A thermal conductivity of 150 W/(m°C) between the solidus and liquidus threshold

temperatures of the alloy in question

- A thermal conductivity of 300 W/(m°C) above the liquidus threshold temperature of the

alloy in question

As with the Mechanical CWM-material model, the activation occurs gradually during the time

takes the thermal energy of the heat source to heat up the quiet weld filler material between its

solidus and liquidus temperatures.

3.3 Mechanical CWM-material model

The mechanical CWM-material model includes three (3) user-defined features:

- A residual stress releasing function

- Isotropic and/or linear kinematic hardening

- Weld filler material activation

The CWM-material model is a thermo-elastic-plastic model with kinematic hardening that

allows for material creation as well as residual stress release triggered by temperature and the

model is, for the time being, limited to solid elements only. The material is initially in an

inactivated state that is called the ghost state, in the literature sometimes referred to as a quiet-

and/or chewing-gum material. In this state the material has the thermo-elastic properties defined

by the:

- Ghost Young’s modulus

- Ghost Poisson’s ratio

- Ghost thermal expansion coefficient

The name “Ghost material” has its origin from the fact that the CWM-analyst from time to time

must reminds himself and the stakeholders that numerical artefacts may heritage from the

inactivated weld filler material’s properties.

These values represent metal empty volumes i.e. vacuum or fluids (air and liquid). In theory,

shall the Young’s modulus value be small enough to not influence the surroundings but large

enough to avoid numerical problems. A quiet material stress should never reach the yield point.

When the temperature reaches the activation (birth) temperature, a history variable representing

the indicator of the welding material is incremented, this variable follows Equation. 1.

Equation. 1. ( ) ( ( ( )

) )

This parameter is available as history variable 9 in the output database. The effective thermo-

elastic material properties are interpolated in accordance with Equation. 2 - ‎Equation. 4.

Equation. 2. ( ) ( )





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The stress update then follows a classical isotropic associative thermo-elastic-plastic approach

with kinematic hardening that is summarized in the following. The explicit temperature

dependence is sometimes dropped for the sake of clarity. The stress evolution is given as

described in ‎Equation. 5.

Equation. 5. ( )

Where C is the effective elastic constitutive tensor and ( Equation. 6) and (‎Equation. 7)

are the thermal and plastic strain rates.

Equation. 6.

Equation. 7.

Equation. 7 include the deviatoric stress, the back stress κ and the effective stress that are

involved in the plastic equations, Equation. 8.

Equation. 8. √

( ) ( )

The effective yield stress (σy) is given as expressed in Equation. 9 and plastic strains evolve

when the effective stress exceeds this value.


The back stress evolves as described in ‎Equation. 10, where p is the rate of effective plastic

strain that follows from consistency equations.

Equation. 10. ( ) ( )

When the temperature reaches the start annealing temperature, the material starts assuming its

virgin properties. Beyond the start annealing temperature it behaves as an ideal elastic-plastic

material but with no evolution of plastic strains. The resetting of effective plastic properties in

the annealing temperature interval is done by modifying the effective plastic strain and back

stress before the stress update as described by ‎Equation. 11 and Equation. 12.

Equation. 11.

( (

))

Equation. 12. ( (

))




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3.3.1 Residual Stress Releasing Function

The residual stress releasing function, also known as annealing- and/or recrystallization function,

gradually releases the back stress tensor and the effective plastic strain when the

material temperature pass through the residual stress release temperature interval (lower- and

upper residual stress release threshold).

The residual stress release function eliminates the prior accumulated hardening history, for

example when the material goes from a solid state to a liquidus state or vice versa (or if there is a

specific solid state phase transformation or recrystallization interval). Here, the user-defined

values at the upper residual stress release threshold temperature are:

- Back stress tensor set to the value zero [ ]

- Effective plastic strain set to the value zero [

]

- Stresses d plastic strains remain unchanged [

]

3.3.2 Residual Stress Release Temperatures

The residual stress release temperature interval, lower- and upper residual stress release

threshold, are defined in the following welding engineering manner by the use of an Iron –

Carbon Phase Diagram, ‎Fig. 3:

- Residual Stress Release Start Temperature: (Lower residual stress release threshold)

TMCP Ferritic steels: Use A1 value from Iron – Carbon Phase Diagram

Normalized Ferritic steels: Use A3 value from Iron – Carbon Phase Diagram

Austenitic steels: Use 1030 °C (exact temperature can be discussed/argued)

- Residual Stress Release Stop Temperature: (Upper residual stress release threshold)

TMCP Ferritic steels: Use A3 value from Iron – Carbon Phase Diagram

Normalized Ferritic steels: Use A3 value + 25 °C

Austenitic steels: Use 1100 °C (exact temperature can be discussed/argued)




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Fig. 3. Iron – Carbon Phase Diagram indicating the A1-, A3-, Solidus- and Liquidus Lines

3.3.3 Hardening Formulation

The material hardening model can employ a mixed hardening with a range from 100% isotropic

hardening to 100% linear kinematic hardening.

3.3.4 Weld filler material activation

The weld filler materials of all weld passes are modelled and participate in the FE-simulation

from the beginning. The weld filler material has two different mechanical properties:

- Ghost, also known as quiet and chewing gum, i.e. inactive,

- Active

Initially, all weld filler material is in the ghost state. It becomes activate as a function of

temperature /54/ in particular, the activation occurs gradually during the time it takes for the

thermal energy of the heat source to heat the ghost weld filler material between its solidus and

liquidus temperatures. The solidus and liquidus temperatures of the actual weld filler material

should be identified by means of its chemical composition in combination with the use of an

appropriate phase diagram.

At the moment of that the weld filler material has become fully activated will it obtain liquid

weld filler material properties and gradually transform to solid weld material properties when its

temperature falls below its liquidus and solidus temperature. This implies that the ghost material

model contains three (3) different material characteristics for one and single material:

- Ghost

- Liquid

- Solid

It also implies that the weld filler material only can build up weld residual stresses after that it

has been activated and/or the temperature has fallen down below its solidus- and residual stress

releasing temperatures.




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4 DNV CWM METHODOLOGY

4.1 Introduction

The DNV CWM-methodology is a substantially improvement of the work carried out 1998 by L.

Josefson and B. Brickstad. /54/ That, for the time being, is a dominating CWM-method adopted

by the Swedish Radiation Safety Authority (2009) as well as TWI (2010). /55/ /56/ /57/ /58/

A number of practical-, commercial-, coding-, academically- and technically related reasons has

contributed to DNV’s “industrial-CWM evolution” ending up to use the commercial FEM-code

LS-Dyna. Nevertheless, a major reason that clearly is differentiating LS-Dyna from other

commercial general non-linear implicit solvers is that LSTC, Livermore Software Technology

Corporation, from the very beginning has concentrated its effort to optimise its code for rapid

solving times of transient dynamic material problems incorporating thermo-dynamic effects.

This has been found very beneficial at FE-weld simulations as the transient thermal load of the

weld heat flux results in an intricate/complex dynamic interaction of contracting weld filler

material at the same time as the base material first expands and finally contract as a function of

that the weld heat flux pass by.

The DNV CWM-methodology package consists of the following approaches that can be

combined in various constellations to meet the specific needs and demands of the actual project:

- Scrutinizing of the actual weld joint configuration including, WPQR, WPS, base- and weld

filler material certificates as well as the material producers’ recommendation

- Experimental test welding and DAQ, Data Acquisitioning, based on the data of the actual

weld joint configuration’s documentation

- 3D thermal FE-simulation of the weld heat flux and temperature fields with activation of

weld filler material

- 3D thermo-mechanical staggered coupled FE-simulation of the weld heat flux, temperature

fields, weld residual stresses and –deformations, including activation of weld filler material

- Axisymmetric thermo-mechanical coupled FE-simulation of the weld heat flux,

temperature fields, weld residual stresses and –deformations, including activation of weld

filler material. By the use of the weld heat flux, obtained from a 3D thermal FE-simulation,

as the weld heat load

- 2D thermo-mechanical coupled FE-simulation of the weld heat flux, temperature fields,

weld residual stresses and –deformations, including activation of weld filler material. By

the use of the weld heat flux, obtained from a 3D thermal FE-simulation, as the weld heat

load




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4.2 Scrutinizing WPQR and WPS

Before the modelling and CWM-simulations begins shall the actual weld joint configuration

including, WPQR, WPS, base- and weld filler material certificates as well as the material

producers’ recommendations be reviewed and scrutinized. As the current conceptual idea of

CWM is that the FE-weld simulations shall be based on weld test experimental data such those

stated in a WPQR or WPS. /44/ /45/ /46/ /47/

4.3 Test Welding and DAQ

If required, experimental test welding and DAQ, Data Acquisitioning, shall be performed by

weld process oriented Welding Engineers in accordance with a quality level that at least are in

accordance with the most stringent requirements of the applicable WPS- and WPQR standard

NORSOK M601.

4.4 Weld Heat Calculations

A fundamental part of CWM-analyses is the calculation and scrutinizing of the weld heat input,

Qw:

- Used at the WPT, Welding Procedure Test

- Stated in the WPQR, Welding Procedure Qualification Record

- Stated on the WPS, Welding Procedure Specification

- Used or intended to be used in the reality

From a welding engineering perspective is the weld heat input, Qw, the amount of energy used to

produce a specific weld pass. The unit is kJ/mm and QW is calculated by ‎Equation. 13. /60/ The

back ground to the equation and the weld process thermal efficiency values has been described

by L-E Svensson. /61/

Equation. 13.

Nomenclature Equation 13:

Qw = Weld Heat Input [kJ/mm]

η = Weld process thermal efficiency

U = Arc Voltage [V]

I = Current [A]

v = Welding speed [mm/s]




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In the case of CWM-analysis should the weld heat input, Qw, of each weld pass be calculated as

weld heat power, Pw, with the unit W, calculated by Equation. 14.

Equation. 14.

Nomenclature Equation 14:

Pw = Weld Heat Power [W]

η = Weld process thermal efficiency

U = Arc Voltage [V]

I = Current [A]

4.4.1 3D Transient FE-Weld Simulations

A Goldak double ellipsoidal weld heat source model is used at 3D transient, thermal and thermo-

mechanical staggered coupled, FE-weld simulations. The weld heat power, Pw, is applied in the

form of a 3D weld heat flux density, QΦ3D, with the unit W/m3, Fig. 4. ‎/44/

Fig. 4. Illustration of LS-Dyna’s Goldak double ellipsoidal weld heat source implementation

The LS-Dyna implementation of the Goldak double ellipsoidal weld heat source model is

described by ‎Equation. 15 – ‎Equation. 18. /62/‎/62/

Equation. 15.

Equation. 16. √

√

( )

Equation. 17. √

√

( )

Equation. 18.

Nomenclature Equation 15 - 18


QΦ3D = 3D Weld Heat Flux Density [W/m3]

= 3D Forward Weld Heat Flux Density [W/m3]

= 3D Aftward Weld Heat Flux Density [W/m3]

ff = Forward end weld heat power deposition factor, ( 0 < Ff < 2)




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fa = Aftward end weld heat power deposition factor, ( 0 < Fa < 2)

a, b, c1, c2 = Radiuses describing the double ellipsoidal shape [m]

x, y, z = Distances (Cartesian coordinates) with the arc emitting node as Origo [m]

v = Weld head travel speed [m/s]

t = Time [s]

4.4.2 2D Transient FE-Weld Simulations

At 2D/Axisymmetric FE-weld simulations the weld heat power, Pw, is applied in the form of an

Equivalent 2D weld heat flux density, QΦ2D, with the unit W/m3.

In the 2D/Axisymmetric CWM-methodology formulated by B. Brickstad and L. Josefson (1998)

is Pw converted to QΦ2D by ‎Equation. 19 - ‎Equation. 20. /54/

Equation. 19.

Equation. 20. ( )

Nomenclature Equation 19 - 20


QΦ2D = Equivalent 2D Weld Heat Flux Density [W/m3]

V2D = 2D Weld Pass Volume [m3]

Aw = Weld Pass Crosse Section Area [m2]

v = Welding speed [m/s]

t1 = Time of the‎weld‎melt‎pool’s‎forward‎edge to pass by the‎weld‎joint’s

cross section plane [s]

t2 = Time of the‎weld‎melt‎pool’s‎aftward edge pass by the‎weld‎joint’s

cross section plane [s]

The application of Equation. 19 - ‎Equation. 20 implies the simplified assumption of that the 2D

weld heat flux density, QΦ2D, has a uniform amplitude during the time it takes for the weld head

and its associated weld melt pool to pass by the weld joint’s cross section plane, Fig. 5. It should

also be mentioned that it is fairly tricky to calculate correct time values of t0 and t1.

Fig. 5. Equivalent 2D weld heat flux density load curve (left); weld joint’s cross section plane (right)




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In the reality is this not the case as the weld heat flux, QΦ, in the way of the cross section plane is

a function of numerous and various weld melt pool related parameters. By the use of an

improved 2D/Axisymmetric weld heat flux density modelling method, formulated by P.

Lindström and L. Josefson (2012), better (more accurate) weld residual stress results are

obtained. /2/ The improved 2D/Axisymmetric weld heat flux density modelling methodology is

as follow:

Step 1

By the use of 3D transient thermal FE-weld simulation is the sum of the resultant heat flux, ∑QΦ,

of all nodes in the cross section plane of the actual weld pass analysed, Fig. 6. The unit of the

∑QΦ–value is W/m3.

Fig. 6. Illustration of ∑QΦ-curve in the plane of a root pass’ cross section plane

Step 2

The 3D transient thermal FE-weld simulation gives fairly accurate ∑QΦ-values for the time

period when the weld melt pool pass over the cross section plane, Fig. 7.

Fig. 7. Q∑Φ-values over time in the plane of a root pass’ cross section

Step 3

The ∑QΦ-curve is used to calculate the Equivalent 2D weld heat flux density, QΦ2D,. This is done




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by collecting and compiling the values from Fig. 7 into an Equivalent 2D Weld Heat Flux

Density Load Curve Table, Table 1.

Table 1

Equivalent 2D Weld Heat Flux Density Load Curve

Time [s]

∑QΦ

[W/m3]

f2D

[ - ]

QΦ2D

[W/m3]

0 2,68E+07

0,7 5,65E+08

2,2 1,33E+10

3,9 2,75E+09

4,4 2,77E+08

5,1 2,28E+08

5,8 5,49E+07




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Step 4

A 2D weld heat flux density scale factor, f2D, is calculated by Equation. 21

Equation. 21.

∫

Nomenclature Equation 21

f2D = 2D weld heat flux density scale factor

∑Q = Total weld heat energy used to produce the entire weld pass [J]

∫

= Integer of the resultant heat flux sum [J]

t0 = Time when total resultant heat flux start to affect the cross section plane [s]

t1 = Time when total resultant heat flux stop to affect the cross section plane [s]

The sum of the weld heat energy for the entire weld pass, ∑Q, is calculated by either ‎Equation.

22 or ‎Equation. 23.

Equation. 22. ∫

Equation. 23. (

)

Nomenclature Equation 22 -23

∑Q = Total weld heat energy used to produce the entire weld pass [J]

Qw = Weld heat input [kJ/mm]

Pw = Weld heat power [W]

lw = Weld pass length [m]

t0 = Start time of welding the pass [s]

t1 = Stop time of welding the pass [s]




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Whilst the integer of the resultant heat flux sum, ∫

, conveniently can be calculated by the

use of LS-PrePost , Fig. 8. /27/

Fig. 8. Integer of the resultant heat flux sum, ∫

, in the plane of a root pass’s cross section

Step 5

The equivalent 2D weld heat flux density load curve table is updated with the f2D-value,

calculated by the use of Equation. 24, Table 2.

Equation. 24. ( )

Table 2


Time [s]

∑QΦ

[W/m3]

f2D

[ - ] QΦ2D

[W/m3]

0 2,68E+07 2,17E-04

0,7 5,65E+08 2,17E-04

2,2 1,33E+10 2,17E-04

3,9 2,75E+09 2,17E-04

4,4 2,77E+08 2,17E-04

5,1 2,28E+08 2,17E-04

5,8 5,49E+07 2,17E-04




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Step 5

The equivalent 2D weld heat flux density load curve table can now completed. This is done by

calculation of QΦ2D, Table 3.

Table 3


Time [s]

∑QΦ

[W/m3]

f2D

[ - ] QΦ2D

[W/m3]

0 2,68E+07 2,17E-04 7,28E+03

0,7 5,65E+08 2,17E-04 1,53E+05

2,2 1,33E+10 2,17E-04 3,61E+06

3,9 2,75E+09 2,17E-04 7,47E+05

4,4 2,77E+08 2,17E-04 7,51E+04

5,1 2,28E+08 2,17E-04 6,19E+04

5,8 5,49E+07 2,17E-04 1,49E+04

Step 6

Finally is the equivalent 2D weld heat flux density load curve updated and adjusted with start

and stop values in such way that it will fit its intended purposes. An example of that is given

in Table 4.

Table 4


Time [s]

∑QΦ

[W/m3]

fQΦ2D

[ - ]

QΦ2D

[W/m3]

0 0 1 0

1,0 0 1 0

1,00001 2,68E+07 2,17E-04 7,28E+03

1,7 5,65E+08 2,17E-04 1,53E+05

3,2 1,33E+10 2,17E-04 3,61E+06

4,9 2,75E+09 2,17E-04 7,47E+05

5,4 2,77E+08 2,17E-04 7,51E+04

6,1 2,28E+08 2,17E-04 6,19E+04

6,8 5,49E+07 2,17E-04 1,49E+04

6,80001 0 1 0

20 0 1 0




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A comparison of the two (2) Equivalent 2D weld heat flux density calculation methods, the

original- versus the method adopted by DNV, demonstrates that the new QΦ2D-method more

accurately describes the rapid thermal transient associated with arc-welding processes. Thereby

facilitating a better simulation of the weld joint’s dynamic expansion and contraction as a

function of that the weld melt pool passes by. Fig. 9.

Fig. 9. Comparison of the Original QΦ2D-method (left) versus the DNV QΦ2D-method (right)




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4.5 2D Transient Thermo-Mechanical FEA

At 2D transient thermo-mechanical simulation of arc welding processes is DNV utilising a

2D/3D Hybrid element formulation, see Fig. 10. This formulation results in a 2D Generalized

Plain Strain performance that is in accordance with the generalized plane strain theory used by

the commercial FEA-code Abaqus. /63/ The theory assumes that the model lies between two

bounding planes, which may move as rigid bodies with respect to each other, thus causing strain

of the “thickness direction” fibres of the model. It is assumed that the deformation of the model

is independent of position with respect to this thickness direction, so the relative motion of the

two planes causes a direct strain of the thickness direction fibres only.

Fig. 10. Illustration of a simply supported 2D/3D hybrid element CWM model resulting in 2D

Generalised Plain Strain performance as defined by the commercial FEA-code ABAQUS. /63/




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4.6 Elastic Shakedown Analyses

Cyclic plastic stain behaviour is generally decomposed into three (3) regimes, see Fig. 11:

- Elastic shakedown

- Plastic shakedown

- Plastic ratcheting

Fig. 11. Illustration of ductile metallic material responses at cyclic loading

Elastic shakedown (b) is defined as the stress or strain level below which there is a no cyclic

plasticity during each cycle. In other words, the condition of the elastic shakedown is obtained

when the plastic deformation occurs during the early cycles but the final steady stat behaviour is

fully elastic due to the build-up of residual stresses.

Plastic shakedown (c) is the condition in which the material experiences reversed plastic

straining during cycling with no further accumulation of plastic deformation.

Plastic ratcheting (d) describes the condition in which the material accumulates some plastic

strain during each cycle.




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5 CWM-STUDY OF RESIDUAL STRESS CONTRIBUTING FACTORS

5.1 Introduction

In order to identify the main contributing and/or driving factors to weld residual stress

magnitudes in ship steel plate materials, the weld residual stresses in the way of an existing

ship’s bilge strake transversal butt weld have been approximated by CWM-analyses, Fig. 12.

Fig. 12. The bilge strake location in a ship structure /64/

Due to uncertainties regarding the actual weld manufacturing process used it was found

necessary to carry out a parametric CWM-study covering a broad range of base material

properties as well as possible thermal- and mechanical boundary conditions at the time of the

production welding.

The weld joint analysed is a double sided butt weld located in the bilge plate (material quality

NV A32), Fig. 13.

Fig. 13. The keel strake transversal butt-weld joint analysed




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5.2 Assessment of the WPS

Before the modelling and simulation work commenced should the actual WPS and its associated

WPQR be scrutinized. Anyhow, a copy of the WPS used at the fabrication of the weld joint

could not be identified and for that sake was the review limited to an assessment of the WPQR .

5.2.1 Weld Joint Geometry and CWM-Models

Based on the combined information from the Ship’s shell expansion plan and the weld joint

geometry detail information in WPQR, see Fig. 14. It was decided to use a 3D transient thermal

FE-weld simulation model as illustrated in Fig. 15 and Fig. 16.

Fig. 14. The weld joint geometry details of the WPQR




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Fig. 15. Weld joint geometry used at the 3D transient thermal FE-weld simulation

Fig. 16. 3D transient thermal FEA model used

Dimensions: 406 x 306 mm and t1 = 30 mm ;t2 = 20 mm

The 3D transient thermal model constituted of a structured mesh utilising LS-Dyna’s 8-node

hexahedral fully integrated selective reduced solid element /65/ with a total number of 131716

solid elements and 140793 nodes, Fig. 17. The mechanical element has a linear displacement

approximation and the corresponding thermal element is a fully integrated 8-node element with

linear temperature approximation. At the 3D transient thermal simulation only the thermal

element was activated.

Fig. 17. 3D transient thermal FEA model’s cross section mesh density




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The 2D transient thermo-mechanical model constituted of a 2D/3D hybrid element formulation

with a 2D Generalized Plain Strain performance in accordance with the generalized plane strain

theory used by the commercial FEA-code Abaqus. /63/ The element type used was LS-Dyna’s 8-

node hexahedral fully integrated selective reduced solid element. /65/ For the full size plate

model was a total number of 8476 solid elements and 140793 nodes used. The mechanical

element has a linear displacement approximation and the corresponding thermal element is a

fully integrated 8-node element with linear temperature approximation.

Fig. 18. 2D transient thermo-mechanical FEA model used, the blue section is the part of the plate

that is used at the final elastic plastic shakedown analyses. Dimensions: 4000 x 3000 mm and t1 = 30 mm ;t2 = 20 mm 2D/3D hybrid element formulation with a 2D Generalized Plain Strain performance /63/

It shall be noted that the cross section mesh density used for the 2D transient thermo-mechanical

model ( Fig. 19) is about 4 times denser compared to the 3D transient thermal model, Fig. 17. For

the sake of capturing local weld residual stresses and deformations as well as avoiding numerical

stress and strain artefacts in the way of the HAZ. /66/

Fig. 19. 2D transient thermo-mechanical FEA model’s cross section mesh density




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5.2.2 Weld Heat Input

An initial 3D transient thermal simulation of the weld joint was carried out with the nominal

weld heat input values stated in the WPQR, Fig. 20 and Table 5.

Fig. 20. Weld arc energy parameters stated in the WPQR

Table 5

Weld Heat Input Values Covered by the WPQR

Pass

[No.]

I

[A]

U

[V] η

V

[cm/min]

Qmin

[kJ/mm]

Qnom

[kJ/mm]

Qmax

[kJ/mm]

Root 400 30 1 32 1,69 2,25 2,81

Run-2 600 32 1 25 3,46 4,61 5,76

Run-3 600 34 1 25 3,68 4,90 6,12

Run-4 500 32 1 28 2,57 3,43 4,29

Run-5 600 34 1 25 3,68 4,90 6,12

Based on the results of the initial 3D transient thermal simulation activity it is understood,

beyond any doubt, that the actual weld joint not could have been produced with weld heat input

values covered by the presented WPQR. As its nominal weld heat input values, Qnom, resulted in

an extremely large weld melt pool, Fig. 21.




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Fig. 21. Weld melt pool temperature and distribution (through the plate penetration) of Run-5

For that sake it was decided to use three (3) different weld heat input magnitudes in order to

illustrate the weld heat input’s influences on the weld residual stress values in the way of the

HAZ, Heat Affected Zone. The values used are presented in Table 6 here below and it shall be

noted that Q-1 and Q-2 heritage from a DNV approved WPQR, Fig. 22 and Table 6. /67/

Table 6

Weld Heat Input Values Used at the CWM-analysis

Q-1 Q-2 Q-3

Pass

[No.]

[kJ/mm]

v

[cm/min]

[kJ/mm]

v

[cm/min]

[kJ/mm]

v

[cm/min]

Root 1,260 50,0 1,680 50,0 1,20 32

Run-2 1,470 52,8 1,960 52,8 2,00 25

Run-3 1,470 52,8 1,960 52,8 2,25 25

Run-4 1,798 48,0 2,397 48,0 2,00 28

Run-5 1,362 54,5 1,817 54,5 2,25 25




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Fig. 22. Weld arc energy parameters stated in WPQR No: 188:00:00

Table 7

Weld Heat Input Values Covered by WPQR No: 188:00:00

Pass

[No.]

I

[A]

U

[V]

η V

[cm/min] [kJ/mm]

[kJ/mm]

[kJ/mm]

Root 500 28,0 1 50,0 1,260 1,680 2,100

Run-2 575 30,0 1 52,8 1,470 1,960 2,450

Run-3 575 30,0 1 52,8 1,470 1,960 2,450

Run-4 650 29,5 1 48,0 1,798 2,397 2,996

Run-5 550 30,0 1 54,5 1,362 1,817 2,271




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5.2.3 Thermal and Mechanical Boundary Conditions

It is not known, in detail, how the butt weld joint in question has been manufactured. For that

reason was the joint welding simulated with three (3) possible types of welding tables. Resulting

in three (3) different thermo-mechanical boundary conditions at the time of production welding,

the alternatives are:

- The plates are placed on a cast steel welding table, tightly/rigidly fixated by wedges,

Alternative 1 in ‎Fig. 23

- The plate are placed on a concrete floor reinforced with heavy steel bars to which the

plates are tightly/rigidly fixated by wedges and/or tack weld joints,


- The plates are welded in a flake line with mechanical compression locking


Fig. 23. Illustration of the three (3) alternative thermo-mechanical boundary conditions at manufacturing of the butt weld joint

The welding simulation was done with an anticipated takt time of 600 seconds (10 min) in the

following welding production sequence:

Takt 1 Fixation of the plates to the welding table at 20 ˚C room temp. , ‎Fig. 24

Takt 2 Welding of Root Pass and cooling at 20 ˚C room temp. , t = 600 s

Takt 3 Welding of Pass-2 and cooling at 20 ˚C room temp. , t = 600 s


Takt 5 Flipping the plate as well as cooling at 20 ˚C room temp. , t = 600 s , ‎Fig. 25

Takt 6 Fixation of the plates to the welding table at 20 ˚C room temp. , ‎Fig. 26



Takt 9 Release of plate and cooling at 20 ˚C room temp. , t = 600 s , ‎Fig. 27




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Fig. 24. Takt 1: Fixation of plates to the three (3) alternative welding tables before welding the Root pass

Fig. 25. Takt 5: Flipping the plates at completion of Pass-3

Fig. 26. Takt 5: Fixation of plates to the three (3) alternative welding tables before welding Pass-4

Fig. 27. Takt 9: Releasing the plates at completion of Pass-5




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During all welding sequences is a 100% thermal- and mechanical bonded contact anticipated

between the plates and the actual welding table. At the flip- and release sequences are the plates

simulated as simply supported, Fig. 28, as described in Chapter 4.5, “2D Transient Thermo-

Mechanical FEA” of this report.

Fig. 28. Illustration of a simply supported 2D/3D hybrid element CWM model

At the welding of the passes Root, Pass-2 and Pass-3 it is anticipated that the weld joint

preparation surfaces of the top side will be covered by weld flux. As well as the void space of

Pass-4 and Pass-5 is filled up and packed with a backing flux or some sort of a ceramic backing

bar, Fig. 29. It implies that there will be almost zero (0) energy transport in the form of

conduction, radiation and/or convection from all weld joint preparation surfaces.

Fig. 29. Illustration of a ceramic backing bar




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During all the weld simulation sequences is all plate and weld metal surfaces simulated to be

exposed to the surrounding work shop atmosphere by the use of an apparent thermal convection

boundary condition. Describing the total amount of heat transfer from the surfaces due to

convection and radiation, Equation. 25 and Equation. 26. /54/ /56/

Equation. 25.

Equation. 26.

5.2.4 Elastic Shakedown Analyses

At completion of the weld production related simulations was a 0,795 m long section of the plate

in the way of the butt weld joint (see Fig. 30) subjected to an elastic shakedown analysis with

boundary conditions and load spectra presented in Fig. 31 and Fig. 32.

Fig. 30. The 0,795 m long plate section subjected to elastic shakedown

Fig. 31. The boundary conditions used at elastic shakedown analyses

Fig. 32. The load spectra used at the elastic shakedown analyses




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5.3 Description of the CWM Analyses Carried Out

The CWM-analyses has been done with the weld filler material combination Y-D/NF310, that

has a typical yield stress, σy = 499 MPa at 20 °C. /68/ The FE-weld simulations has been done

with respect to the as “elastic shakedown condition” of weld residual stresses (σxx-, σyy- and σzz-

stresses) along Line A, -B, -C and –D in the way of a butt weld joint, as illustrated in ‎Fig. 33.

Fig. 33. Illustration of the residual stress (σxx; σyy; σzz) sampling lines weld

In order to study and explain the base materials’ influences on the resulting weld residual stress

magnitude have a total number of 18 simulations been carried out for two (2) different types of

base materials. Simulated to be welded with the weld filler material combination Y-D/NF310,

that has a typical yield stress, σy = 499 MPa at 20°C. /68/ The base materials are:

- Grade NV A, with a minimum yield stress, σy = 235 MPa at 20°C

- Grade NV AH32, with a typical yield stress, σy = 417 MPa at 20°C

An overview of the 18 different simulations carried out is presented in Table 8 and Fig. 34 here

below.




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Table 8

Weld Simulations Carried Out

Weld filler material combination Y-D/NF310

(σy = 499 MPa @ 20°C)

Altern

ative

Grade NV A

(σy = 235 MPa at 20°C)

Grade NV AH32

(σy = 417 MPa at 20°C)

Q-1 (Qmin)

Q-2 (Qnom)

Q-3 (Qmax)

Q-1 (Qmin)

Q-2 (Qnom)

Q-3 (Qmax)

1 NVA

Alt1-Q1

NVA

Alt1-Q2

NVA

Alt1-Q3

NVAH32

Alt1-Q1

NVAH32

Alt1-Q2

NVAH32

Alt1-Q2

2 NVA

Alt2-Q1

NVA

Alt2-Q2

NVA

Alt2-Q3

NVAH32

Alt2-Q1

NVAH32

Alt1-Q2

NVAH32

Alt2-Q3

3 NVA

Alt3-Q1

NVA

Alt3-Q2

NVA

Alt3-Q3

NVAH32

Alt3-Q1

NVAH32

Alt3-Q2

NVAH32

Alt3-Q3

Fig. 34. Illustration of the three (3) alternative thermo-mechanical boundary conditions at manufacturing of the butt weld joint

5.3.1 Material properties and modelling

The minimum yield stress (σy) of the base material NV A is 235 MPa at 20°C and it will

experience kinematic hardening during the thermo-mechanical deformations of the weld process

cycles. /69/ /70/ The residual stress release temperature interval used for NV A is 735 – 870 °C.

A typical yield stress (σy) of the base material NV AH32 produced in Japan around year

1996/1997 has been found to be about σy = 417 MPa at 20 °C, Appendix A. The steel plate will

experience kinematic hardening during the thermo-mechanical deformations of the weld process

cycles. /69/ /70/ The residual stress release temperature interval used for NV AH32 is 735 – 870

°C.

The yield stress (σy) of the weld filler material combination Y-D/NF310 is 499 MPa at

20 °C and it will experience kinematic hardening during the thermo-mechanical deformations of

the weld process cycles. /68/ The weld filler material activation temperature interval used for Y-

D/NF310 is 1510 – 1538 °C and the residual stress release temperature interval is 890 – 915 °C.

A 100% Linear Kinematic hardening formulation was used for the base- and the weld filler

materials in order to simulate the hardening during the thermo-mechanical deformations of the

weld process cycles. /2/ /54/ /55/ /56/




Essen, Germany

5.4 Weld Residual Stress Results - Elastic Shakedown

The sampling lines of “As Shakedown” residual stress (σxx ; σyy ; σzz) results in the way of the

weld joint at 20 °C are presented in Fig. 35.

Fig. 35. Illustration of the weld residual stress (σxx; σyy; σzz ) sampling lines

Table 9 Weld Simulations “As Shakedown” Residual Stress (σxx ; σyy ; σzz) Results

Weld filler material combination Y-D/NF310 (σy = 499 MPa @ 20°C)

Altern

ativ

e

Grade NV A

(σy = 235 MPa at 20°C) Grade NV AH32

(σy = 417 MPa at 20°C)

Q-1

(Qmin)

Q-2

(Qnom)

Q-3

(Qmax)

Q-1

(Qmin)

Q-2

(Qnom)

Q-3

(Qmax)

1 Chapter 5.4.1 Chapter 5.4.4 Chapter 5.4.7 Chapter 0 5.4.1 Chapter 5.4.4 Chapter 5.4.7

2 Chapter 5.4.2 Chapter 5.4.5 Chapter 5.4.8 Chapter 5.4.2 Chapter 5.4.5 Chapter 5.4.8

3 Chapter 5.4.3 Chapter 5.4.6 Chapter 5.4.9 Chapter 5.4.3 Chapter 5.4.6 Chapter 5.4.9

Table 10

Weld Heat Input Values Used at the CWM-analysis

Q-1 Q-2 Q-3

Pass

[No.]

[kJ/mm]

[kJ/mm]

[kJ/mm]

Root 1,260 1,680 1,20

Run-2 1,470 1,960 2,00

Run-3 1,470 1,960 2,25

Run-4 1,798 2,397 2,00

Run-5 1,362 1,817 2,25




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5.4.1 Weld Residual Stress Results – Alternative 1 and Qmin

Fig. 36. Weld residual stresses (σxx) “As Shake Down”: NV A Left and NV AH32 Right

Fig. 37. Weld residual stresses (σyy) “As Shake Down”: NV A Left and NV AH32 Right

Fig. 38. Weld residual stresses (σzz) “As Shake Down”: NV A Left and NV AH32 Right




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5.4.2 Weld Residual Stress Results – Alternative 1 and Qnom







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5.4.3 Weld Residual Stress Results – Alternative 1 and Qmax







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Essen, Germany

6 DISCUSSION

6.1 Thermo- and Mechanical Boundary Conditions

From the results of the parametric butt weld joint calculations it can be concluded that when one

is using exactly the same weld process parameters and production sequence. For exactly the

same base- and weld filler material will the magnitudes of the weld residual stresses depend on

the thermo- and mechanical boundary conditions utilised at the manufacturing process, Fig.

63, Fig. 64 and Table 11.

Fig. 63. Weld residual stresses (σxx) “As Shake Down” produced on welding table Alternative 1

Base material Grade NV AH32 (σy = 417 MPa at 20°C) Weld filler material combination Y-D/NF310 (σy = 499 MPa @ 20°C)

Fig. 64. Thermo-mechanical boundary condition Alternative 1 (left) and Alternative 3 (right)

Table 11

Weld Heat Input

Q-2

Pass

[No.]

[kJ/mm]

Root 1,680

Run-2 1,960

Run-3 1,960

Run-4 2,397

Run-5 1,817




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6.2 Weld Heat Input

It has also been noticed that the magnitudes of the weld residual stresses are dependent on the

weld heat input, Q, which in combination with the base material’s thermal properties and the

surrounding thermal boundary conditions controls the weld cooling rate. /14/ A low weld heat

input, Qmin, results in higher weld residual stress magnitudes compared to a high weld heat input,

Qmax, Fig. 65, Fig. 66 and Table 12


Qmin – left and Qmax - right Base material Grade NV AH32 (σy = 417 MPa at 20°C) Weld filler material combination Y-D/NF310 (σy = 499 MPa @ 20°C)

Fig. 66. Thermo-mechanical boundary condition Alternative 3

Table 12

Weld Heat Input

Q-1 Q-3

Pass

[No.]

[kJ/mm]

[kJ/mm]

Root 1,260 1,20

Run-2 1,470 2,00

Run-3 1,470 2,25

Run-4 1,798 2,00

Run-5 1,362 2,25




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6.3 Yield Stress Difference

The magnitudes of the weld residual stresses appear, to a minor extent, to depend on the yield

stress difference between the base material and the weld filler material. A low yield stress

difference value is indicated to result in a low residual stress value whilst a high yield stress

difference value is indicated to result in a high residual stress value, Fig. 67, Fig. 68 and Table

13.


Weld filler material combination Y-D/NF310 (σy = 499 MPa @ 20°C) Base material Grade NV A (σy = 235 MPa at 20°C - left Base material Grade NV AH32 (σy = 417 MPa at 20°C) – right

Fig. 68. Thermo-mechanical boundary condition Alternative 1

Table 13

Weld Heat Input

Q-1

Pass

[No.]

[kJ/mm]

Root 1,260

Run-2 1,470

Run-3 1,470

Run-4 1,798

Run-5 1,362




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7 CONLUSIONS

Based on the results of the parametric CWM analyses carried out it can be concluded that the

following factors are contributing and/or driving the magnitude of the weld residual stress

values:

Thermal- and Mechanical Boundary Conditions during the production welding

Yield stress difference between the base- and the weld filler material

Weld heat input, Q, which affects the weld cooling time




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8 REFERENCES

/1/. Goldak, J., Akhlaghi, M., 2005, Computational Welding Mechanics, ISBN:

9780387232874,Springer-Verlag New York Inc., USA

/2/. Lindgren, L.-E., 2007, Computational Welding Mechanics, ISBN: 1845692217, Woodhead

Publishing, UK

/3/. Lindström, P. R. M., Josefson, B. L., 2012, 2D, Axisymmetric and 3D Finite Element Analysis

Assessment of the IIW RSDP Round Robin Initiative, Phase 1 and Phase 2, IIW Document No.

IIW-X-1712-12, IIW-XIII-2437-12 and IIW-XV-1412-12, IIW General Assembly 2010, Denver,

USA

/4/. Josefson, B. L., Lindström, P., and Molin, M., 2010, 2D and 3D Simulation of the IIW Round

Robin Benchmark”, IIW Document No. IIW-XIII-2325-10, IIW General Assembly 2010,

Istanbul, Turkey

/5/. Cox, D. S., 2011, Repair of the NRU Reactor Vessel: Technical Challenges and Lesson Learned,

International Conference on Research Reactors: Safe Management and Effective Utilization,

November 2011, Rabat, Marocco

/6/. Goldak, J., Yetisir, M., and Pistor, R., 2012, “The Role of Computational Weld Mechanics in the

Weld Repair of Canada’s NRU Nuclear Reactor, Welding and Repair Technology for Power

Plants, Tenth International EPRI Conference, EPRI, June 26-29, 2012, Marco Island, Florida,

USA

/7/. Pakhamaa, A., Wärmefjord, K., Karlsson, L., Soderberg, R., and Goldak, J., 2012, Combining

variation with welding simulation for prediction of deformation and variation of a final assembly,

International Journal of Computing and Information Science in Engineering, Vol. 12, to appear.

/8/. Wohlfart, H., Nitscke-Pagel, Th., Diger, K., Siegel, D., and Brand, M., 2010, IIW Round Robin

Residual Stress Calculations and Measurements FINAL REPORT, IIW Document No. IIW-X-

1686-10, IIW-XIII-2349-10 and IIW-XV-1359-10, IIW General Assembly 2010, Istanbul, Turkey

/9/. Smith, M.C., Bouchard, P.J., Turski, M., Edwards, L. and Dennis, R.J., 2012, Accurate prediction

of residual stress in stainless steel welds, Computational Materials Science, Vol. 54, pp. 312-328.

/10/. Muransky, O., Smith, M.C., Bendeich, P.J., Holden, T.M., Luzin, V., Martins, R.V., and

Edwards, L., 2012, Comprehensive numerical analysis of a three-pass bead-in-slot weld and its

critical validation using neutron and synchrotron diffraction residual stress measurements,

International Journal of Solids and Structures, Vol. 49, pp. 1045-1062.

/11/. Wohlfart, H., Nitscke-Pagel, Th., Dilger, K., Siegel, D., Brand, M., Sakkiettibutra, J. and Loose,

T., 2012, Residual Stress Calculations and Measurements – Review and Assessment of The IIW

Round Robin Results, Welding in the World, 09/10 2012, Vol. 56, pp. 120-140.

/12/. Farajin, M., Nitscke-Pagel, Th., and Siegel, D., 2013, Welding Residual Stresses in Tubular Steel

Joints and Their Behavior Under Multiaxial Loading, IIW Document No. IIW-XIII-2477-13, IIW

General Assembly 2013, Essen, Germany

/13/. Lindström, P. R. M., Faraij, M., “Review and selection of a Finite Element Simulation Platform

For Academic and Industrial Analyses of In-Service Welding operations” (2004) ASME 23rd

International Conference on Offshore Mechanics and Arctic Engineering, Vancouver, Canada

/14/. Lindström, P. R. M., 2009, “Heat Transfer Prediction of In-Service Welding in a Forced Flow of

Fluid”, ASME Journal of Offshore Mechanics and Arctic Engineering, Vol. 131, pp 031304-1 -

031304-6

/15/. ISO 3434-2, 2005, Quality requirements for fusion welding of metallic materials - Part 2:

Comprehensive quality requirements

/16/. Lindström, P. R. M., Josefson, B.L., Schill, M., and Borrvall, T., 2012, “Constitutive Modeling

and Finite Element Simulation of Multi Pass Girth Welds”, NAFEMS NORDIC Conference:

Engineering Simulation, Gothenburg, Sweden

/17/. Janosch, J.-J., 2008, International Institute of Welding work on residual stress and its application

to industry, International Journal of Pressure Vessels and Piping, Vol. 85, pp. 183-190




Essen, Germany

/18/. Wohlfahrt, H., 1997/2004 IIW “Round Robin” Update-Results for Residual Stress and Distortion

Prediction, IIW-X/XII/XV-RSDP-97-04

/19/. www.cenaero.be/Page_Generale.asp?DocID=21686&la=1&langue=EN

/20/. www.goldaktec.com

/21/. http://windows.microsoft.com/en-US/windows7/products/home

/22/. www.centos.org

/23/. www.cendio.com/products/thinlinc/

/24/. LSTC, Livermore Software Technology Corporation, USA, www.lstc.com

/25/. LS Dyna 971, Release 7.0.0, Double Precision MPP Solver, Livermore Software Technology

Corporation, USA

/26/. Jurinic, A., 2012, Arc welding simulation with Abaqus/Std, Simulia EuroNordics, Private

communication

/27/. Belytschko, T., Liu, W. K., and Moran, B., 2000, Nonlinear Finite Elements for Continua and

Structures, ISBN: 9780471987741, John Wiley & Sons Ltd, UK

/28/. Simo, J. C., Hughes, T. J. R., 2000, Computational Inelasticity, ISBN: 9780387975207, Springer-

Verlag New York Inc., USA

/29/. Lemaitre, J., Chaboche, J.-L., 1994, Mechanics of Solid Materials, ISBN: 9780521477581,

Cambridge University Press, UK

/30/. www.lstc.com/download/manuals

/31/. Goldak, J., Chakravarti, A., and Bibby, M., 1985, A Double Ellipsoid Finite Element Model for

Welding Heat Sources, IIW Document No. 212-603-85, International Institute of Welding

/32/. Carslaw, H. S., Jaeger, J. C., 1986, Heat Conduction in Solids, ISBN: 9780198533689, Oxford

University Press, UK,

/33/. Shlichting, H., Gersten, K., Boundary Layer Theory, 9783540662709, Springer-Verlag Berlin and

Heidelberg GmbH Co. K, Germany

/34/. Eckert, E. R. G., Drake, R. M. Jr., 1987, Analysis of heat and mass transfer, ISBN: 3-540-17708-

6, Springer Verlag, Berlin, Germany

/35/. LS-PrePost 3.2, 2012, Livermore Software Technology Corporation, USA

/36/. www.notepad-plus-plus.org

/37/. www.nedit.org

/38/. www.vim.org

/39/. Shah, Q., Abid, H., 2012, LS-Dyna for Beginners, ISBN: 9783846556771, LAP Lambert

Academic Publishing AGCo KG, Germany

/40/. www.truegrid.com

/41/. www.amazon.com/kindle-store-ebooks-newspapers-blogs

/42/. www.adlibris.com/letto

/43/. www.iiwelding.org/Qualification_certification/Certification/Pages/IIWPersonnelCertificationSystem.aspx

/44/. Goldak, J., Paramjeet, G. K., and Bibby, M., 1990, Computer simulation of welding processes,

ASME Winter Annual Meeting Symposium on Computer Modeling and Simulation of

Manufacturing Processes, Producxtion of Engineering Division, pp. 193

/45/. Lindgren, L.-E., 2001, Finite element modeling and simulation of welding. Part 1 : Increased

complexity, Journal of Thermal Stresses, Journal of Thermal Stresses, Volume 24, No. 2, pp. 141-

192

/46/. Lindgren, L.-E., 2001, Finite element modeling and simulation of welding. Part 2 : Improved

material modeling, Journal of Thermal Stresses, Journal of Thermal Stresses, Volume 24, No. 3,

pp. 195-231

/47/. Lindgren, L.-E., 2001, Finite element modeling and simulation of welding. Part 3 : Efficiency and

integration, Journal of Thermal Stresses, Journal of Thermal Stresses, Volume 24, No. 4, pp. 305-

334

http://www.cenaero.be/Page_Generale.asp?DocID=21686&la=1&langue=EN

http://www.goldaktec.com/

http://windows.microsoft.com/en-US/windows7/products/home

http://www.centos.org/

http://www.cendio.com/products/thinlinc/

http://www.lstc.com/

http://www.lstc.com/download/manuals

http://www.notepad-plus-plus.org/

http://www.nedit.org/

http://www.vim.org/

http://www.truegrid.com/

http://www.amazon.com/kindle-store-ebooks-newspapers-blogs

http://www.adlibris.com/letto

http://www.iiwelding.org/Qualification_certification/Certification/Pages/IIWPersonnelCertificationSystem.aspx




Essen, Germany

/48/. The Procedure Handbook of Arc Welding, 2012, 14th Edition, The James F. Lincoln Arc

Welding Foundation, Cleveland, Ohio, USA

/49/. SSAB Welding Handbook, 2012, 1st Edition, ISBN: 978-91-978573-0-7, SSAB Oxelösund AB,

Oxelösund, Sweden

/50/. SSAB Sheet Steel Formin Handbook, 1998, SSAB Tunnplåt AB, Borlänge, Sweden

/51/. SSAB Sheet Steel Joining Handbook, 2004, SSAB Tunnplåt AB, Borlänge, Sweden

/52/. Material model: MAT_THERMAL_CWM (MAT_T07), LS Dyna 971, Release 7.0.0, Livermore

Software Technology Corporation, USA

/53/. Material model: MAT_CWM (MAT_270), LS Dyna 971, Release 7.0.0, Livermore Software

Technology Corporation, USA

/54/. B. Brickstad, B.L. Josefson, 1998, A parametric study of residual stresses in multi-pass butt-

welded stainless steel pipes, International Journal of Pressure Vessels and Piping, Vol. 75, pp. 11-

25

/55/. Zang, W., Gunnars, J., Mullins, J., Dong, P., and Hong, J. K. 2009, Improvement and Validation

of Weld Residual Stress Modelling Procedure, Report 2009:15, ISSN: 2000-0456, Swedish

Radiation Safety Authority, Stockholm, Sweden

/56/. Mullins, J., Gunnars, J., 2009, Influence of Hardening Model on Weld Residual Stress

Distribution , Report 2009:16, ISSN: 2000-0456, Swedish Radiation Safety Authority,

Stockholm, Sweden

/57/. Zang, W., Gunnars, J., Mullins, J., Dong, P., and Hong, J. K. 2009, Effect of Welding Residual

Stresses on Crack Opening Displacement and Crack-Tip Parameters, Report 2009:17, ISSN:

2000-0456, Swedish Radiation Safety Authority, Stockholm, Sweden

/58/. Wei, L., He, W., 2010, Comparison of Measured and Calculated Residual Stresses in Steel Girth

and Butt Welds, Report no. 924/201, TWI Ltd, Cambridge, UK

/59/. Wohlfahrt, H., 2009, Report on the Round Robin Tests on Residual Stresses 2009 Joint Working

Group of Commission X/XIII/XV, IIW Document Nos. IIW- X-1668-09 , IIW-XIII-2291-09,

IIW-XV-1326-09

/60/. NS-EN 1011-1:2009,Page 10 – 11, Ch.8 Sec.7, “Heat input”

/61/. Svensson, L.-E., 1993 ,Control of Microstructure and Properties in Steel Arc Welds, ISBN:

9780849382215, CRC Press Inc, USA

/62/. Shapiro, A. B., Heat Transfer in LS-Dyna, 2003, Proceedings of the 4th European LS-DYNA

Conference. 22nd - 23rd May 2003, Ulm, Germany

/63/. Abaqus Theory Manual 6.11, Chapter 3.2.7 Generalized Plain Strain, Simulia

/64/. IACS Recommendation 82, “Surveyors Glossary – Hull Terms & Hull Survey Terms”, 2003,

IACS, London, UK

/65/. Page 3.16 – 3.18, Ch.3 Sec.4, “Fully Integrated Brick Elements and Mid-Step Strain Evolution”,

LS Dyna Theory Manual, March 2009, Livermore Software Technology Corporation, USA

/66/. Oddy, A. S., McDill, J. M. J., Goldak, J. A., 1990, Consistent Strain Field in 3D Finite Element

Analysis of Welds, Journal of Pressure Vessel Technology, Vol. 112, pp. 309-311

/67/. WPQR nr: 188:00:00, 2008, Junoverken AB, Uddevalla, Sweden

/68/. Report on the renewal approval test of automatic and semi-automatic welding materials, 2011,

Report No.: 11124, 06 October 2011, Nippon Steel & Sumikin Weldding Co., Ltd., Narashino-

City, Chiba-Pref., Japan

/69/. DNV Rules for Classification of Ships - January 2013, Part 2 Materials and Welding,

Ch. 2 Sec. 1 - Page 16, DNV, Høvik, Norway

/70/. DNV-OS-B101 Metallic Materials, - October 2012, Ch.2 Sec.1 - Page 19, DNV, Høvik, Norway

- o0o -

APPENDIX A

NV GRADE EH32

APPENDIX B

MATERIAL & PHYSICAL

DATA

Density

Reference: EN 12952-3:2001

Thermal Conductivity

Reference: X-1464-00 XV-1061-00 X-XV-RSDP-55-00

IIW Round Robin on residual stress and Distortion prediction Phase 1 Results

Specific Heat Capacity



Young’s Modulus



Poisson’s Ratio



Yield Stress

References: X-1464-00 XV-1061-00 X-XV-RSDP-55-00


DNV Rules for Ships, Part 2, Chapter 2 and 3

Report on renewal approval test of welding consumable – flux combination

“Y-D / NF310”, No. 11124, DNV

Plastic Modulus



Thermal Expansion

Reference: EN 12952-3:2001

Apparent Thermal Boundary Layer

References: SSM Rapport 2009-16

Mullins, J., Gunnars, J., 2009, Influence of Hardening Model on Weld Residual Stress Distribution ,

Report 2009:16, ISSN: 2000-0456, Swedish Radiation Safety Authority, Stockholm, Sweden

Apparent Boundary Layer

Cm

WTCTC hh 2

0668.050020@

Apparent Boundary Layer

Cm

WTCT hh 2

231.0500@

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