1

Dr.-Ing. Tobias Loose30.11.2012

Material Data for Welding Simulation

Herdweg 13, D-75045 Wössingen Lkr. KarlsruheCourriel: loose@tl-ing.de Web: www.tl-ing.de, www.loose.at

Mobil: +49 - 176 6126 8671 Tel: +49 - 7203 329 023 Fax: +49 - 7203 329 025

2

About Ingeneering Office Tobias Loose

Numerical Simulation forWelding and Heat Treatment

Consulting - Training - SupportSales of software for

Welding and Heat Treatment Simulation

Welding Simulation since 2004Analysis of distortion and residual stressesof large stuctures

Vicechairman of FA I2 of DVSAdvisory Group for research in welding simulation

Vicepresident of FördervereinWärmebehandlung und Schweißen e.V.(Associacion for Promotion of Welding and Heat Treatment Simulation)

unsere Partner

3

Radaj -Triangle on Welding Simulation

MaterialSimulation

ProcessSimulation

StructureSimulation

WeldingSimulation

4

Welding Advisory System

WeldWare®

WeldWare®: Research across decades combined in one software:Heat management during welding of steel - structure transformations and properties in the heat affected zone

Software for Welding SimulationWeldWare® - Materialdata and facil calculations

5

SimWeld

SimWeld comprises long term research and developement for user friendly welding process simulation performed by

Welding and Joining Institute

of RWTH Aachen.

Software for Welding SimulationSimWeld - welding process simulation

6

technical features of Simufact.welding:• easy and quick use• take into account welding specific boundary conditions• quick definition of clamps• suitable for all established welding processes• covers all weld praparations• most important material data available• unfailing calculation

Software for Welding Simulationsimufact.welding - welding structure analysis

7

like to visit us in www?

www.tl-ing.de - www.loose.atwww.simweld.info

look here:

8

What is the motivation for welding simulation?

After welding is not befor welding

Material properties, the shape and the state of stresses are modified.

Weldability test Rheinbridge Breisach (Germany-France) St 37 von 1962Weld-point-bending test according to Steidl

9

What is special in welding simulation

• Temperature• Microstructure with phase transformation• Strain hardening• Reset of material history at melting point

• Thus all material properties needs to be defined– temperature dependend– phase dependendend

• Phase transformation requirese– Phase transformation kinetic– Phase transformation effects

• transformation strain• transformation plasticity

– Mixing law

10

WeldWare®

Welding advisory systemEnergy per length - Preheating - Microstructure

WeldWare® serves…

• the calculation of the heat management befor welding• the calculation of microstructure and mechanical properties in the HAZ• the determination of necessary preheating temperatures at real components• the supply of data for Finite Element Analysis

WeldWare® uses…

• heat comprehensive regression equations

• welding-CCT-diagrams measured by SLV Mecklenburg-Vorpommern GmbH

• corresponding material data

• cooling time equations

choose material data and adjust chemical composition

default chemical composition of database.Values can be modified

Charge Managementuser charges can be saved in database.

Data check. Values needs to be in the range of the regression limits.

Data Export for FEM

continue Weld Ware

Chargemanagement

Add further charges with own number or name.

Any charges can be saved and later on reloaded.

Calculate Phase proportion

Precalculation of microstructurer in HAZ conceerning chemical analysis.

Estimate K30 Value

K30-Value describes the cooling rate to get less than 30 % martensit. Necessary minimum cooling rate to avoid cracks as a result of martensit and hard spot.

Display Welding CCT

The welding CCTs base on austinitisation temperature 1350 °C

Mechanical properties in HAZ ...

• Hardness• Yield strength• Ultimate strengt• Ultimate strain• Contraction at fracture

depending on cooling rate:

… display of mechanical properties over cooling rates

Estimation of welding parameterscalculation of minimum cooling rate

Welding prarmeter to get save the

K30-value

21

SimWeldWelding process simulation

Calculation of Weldpool

22

Input and output parameter for process simulation

Inputparameter:• wire speed• shielding gas• welding velocity• currency / voltage• torch angel• weldposition• geometry of specimem

Output parameter:• weldpool geometry• penetration / undercut• weldability• temperature over time and droplet• controllparameter: weldcurrency, voltace between specimen and torch

Simulation time between 0,5 and 2 minutes

23

Material properties for welding process simulation

24

Material properties for welding process simulation

25

Material properties for welding process simulation

26

Material properties for welding process simulation

27

SimWeldExample to show the

Workflow

28

Example: Fillet weld to show the SimWeld - Workflow

29

Fillet weld - Variante 1

30

Fillet weld - Arc and droplet

31

Fillet weld - Results Variante 1

32

Fillet weld - modified parameter Variante 2

increase welding speed from 25 cm/min to 50 cm/min

increase wire speedfrom 6 m/min to 10 m/min

33

Fillet weld - results Variante 2

34

Thermal cycle and weld-pool Variante 2

Liquidus

Solidus

35

Comparison of fillet weldsVariante 1 - Variante 2

Welding speed: 25 cm/min 50 cm/minWire speed: 6 m/min 10 m/min

36

Example for butt weld

Welding speed: 50 cm/min 30 cm/minWire speed: 6 m/min 10 m/min

37

Simufact.weldingWelding structure analysis

distortion - residual stresse - microstructure

38

Welding structure analysis workflow of model setup

Description of geometryof specimen - CAD

Method of Finite Elements

FEM

Devide in finte elementsMeshing

WeldingDefinition of equivalent heat source

Material Material properties

Process and setupAllocate material properties

define weld sequence, clamps, loads

39

Easy model setup with simufact.welding

40

Structure mechanicStructure mechanicDiffusion - carbonatisation Diffusion - carbonatisation

Hydrogen diffusionHydrogen diffusionElektromagnetismElektromagnetism

Temperature

Grain size

Phase transformation

Temperature

Grain size

Phase transformation

Coupled analysisphysics taken into account

41

Description of phase transformationCCT and IT

Thermodynamic propertiesThermal conductivityDensitySpecific heat

or Enthalpie

Mechanical propertiesYoungs modulusYield strenghtStrain hardeningThermal strainPoisson coefficient

Material properties for welding structure analysis

Johnson-Mehl-Avrami-KolmogorovKoinstinen-MarburgerLeblond modelNancy modelGrong models

42

Phasetransformation - welding steels

Ferritic-perlitic phase (Basematerial)

Hea

tin

g

Austenitisc phase

Coo

ling

increasing cooling rate

Ferrit / Perlit MartensitBainit

krz

kfz

krztrz

43

Temperature in °C

Th

erm

al s

trai

n in

%

kfz

transformation strainthermal strain

Transformation strain and transformation plasticity

krz

Transformation plasticity is an aditional strain that occurs when transformation takes place under load.

44

Stress-strain curve

Models to describe stress-strain curves:

• ideal elastic (not suitable)• ideal elastic ideal plastic (not suitable)

• isotropic hardening• kinematic hardening• mixed isotropic-kinematic hardening• cycle plasticity:

– Armstrong-Frederick– Chaboche

• annealing, postweld heat treatment:– viscoplasticity (creep)

45

Stress-strain-curve

σ true

εtrue,plastic

Re

σtrue, hardening

εtrue

46

Yield strength Re

Temperature in °C

Yie

ld s

tren

gth

Re i

n N

/mm

²

Stress-strain-curve yield

Yield strength as function depending on microstructure and temperature.

47

Stress-strain-curve strain hardening

Strain hardening stress as a group of functions for every phase depending on temperature.

true plastic strain pl in m/m

tru

e h

ard

enin

g st

ress

v i

n N

/mm

²

Hardening Ferrit-Perlit S355

48

Removal of plastic strain at melting point

At melting point the strain hardening disappears. Thus the material is reset to origin without hardening. This dishardening is taken into account by reset of platic strain.

without removal

with removal

49

Removal of plastic strain at melting point

Comparison of longitudinal stress with removalwithout removalof plastic strain.

Simulation is performed without phase transformation.

50

Residual stresses after welding

longitudinal stress

51

Evaluation of longitudinal stress during welding

52

Distortion

53

Evaluation of Distortion

54

ValidationStructural welding analysis

55

• Plate with dimension270 x 200 x 30 mm3 with V/U-shape groove

• austenitic steel (316LNSPH, kf = 275 MPa)

• 2 Layer weld with same filler material as base material: 316L

• TIG Welding with U = 9 V, I = 155 A, v = 0,67 mm/s

IIW Round Robin TestBenchmark for steel without phase transformation

Prof. Dr.-Ing Helmut WohlfahrtDr.-Ing. Marcus Brand

Dipl.-Ing. Jens SakkiettibutraDr.-Ing. Tobias Loose

56

Welding direction

Welding direction

longitudinal stress

transversal stress

IIW Round Robin Test

• Isotropic hardening law was used.• Bauschinger effect disappears at temperature over 400 °C• Signficant influence of strain hardening for evaluation of residual stresses

57

S355E = 5,83 kJ/cmv = 1,66 mm/s

Nitschke-Pagel TestBenchmark for steel with phase transformation

Measurement: Dr. Nitschke-Pagel, Simulation: Dr. Loose

Distortion measured: w = 0,34 mmDistorion calculated: w = 0,32 mm

58

Nitschke-Pagel Test

59

Conclusion and outlookMaterial data for welding simulation

60

Conclusion and outlook

• The request for material data needed for welding simulation in general was shown

• most important:– temperature dependency

– microstructure dependency

– history dependency

• What is needed in investigation in material properties:– get correct material properties phase dependend

– get the right mixing law

– take into account the material history

– get damage criteria:• cold crack, damage after welding, service or ultimate load

• hot crack

• fatique

61

Thanks for your attention ...... any questions?