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Dr.-Ing. Tobias Loose17.11.2010
Welding Simulationand calculation of residual stresses
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Causality
1. Welding torch2. Temperature field3. Elongation - shrinking Mechanical response of component → Residual stresses and distortion
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Residual stress - Distortion
Residual stress
Distortion
free shrinkingsoft structurenot clamped
shrinking disabledstiff structurefully clamped
. . Optimum . .
Large distortionRisk of process failure
High plastic strainRisks of in service failure
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Why Welding Simulation?
After welding,the material does not behave like bevor.
Specimem from Rhein Bridge BreisachSt 37 from 1962Spot weld bending test according to Steidl
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Results of Welding Simulation
• Temperatur evaluation during welding• Microstructure• Hardness• Residual stesses and strains• Remaining plasticity - ductility• Yield stress in weld and HAZ• strainrate during welding
The evaluation of these results enables estimations - overheating of workpiece- quality of weld- crack- fatique- ultimate load and - behaviour under service load
55 % Ms 0 %
50 %Phase-proportion Ms
Mikroschliff von:
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Most important: Micostructure
Strength depends on microstructure
Ferrit- Perlit (Base Material)he
atin
g
Austenit
cool
ing
increasing cooling rate
Ferrit / Perlit MartensitBainit
α
γ
α
krz
kfz
krztrz
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Temperature in °C
Ther
mal
stra
in in
%
γkfz
phase-transformation strainthermal strain
Most important: Micostructure
αkrz
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Most important: MicrostructureCCT and IT - description of phase transformation
Phase Transformation Calibration Managerautomatic calibration of CCT and IT Diagrams for
SYSWELD
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Yield Re
Temperature in °C
Yie
ld R
e in
N/m
m²
Most important: material properties
Material propertiesas a function of temperature and microstructure
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Most important: reset of plastic strains
When material is molten or in case of phase transformation Austenit - Martensit the plastic strains has to be set back to zero.
without reset
with reset
cum
ulat
ed p
last
ic st
rain
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Most important: material propertiesMaterial Database Manager
Thermal material propertiesThermal konduktivityDensity Specific heat or Enthalpy
Mechanical material propertiesE-ModulYieldSlope (strain hardening)Thermal strainPoisson Coefficient
Description of phase transformationIT and CCT
Material Database Managerto manage complex material data easilyfor Welding Simulation with
SYSWELD
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Available material data
For many materials data for welding simulation with SYSWELD are available:
DP-W-600TRIP700ZDC04 S355516_Grade_70X80TA1050Nirosta_H400X20Cr13X5CrNi1810CF35316L16MnCr5100Cr6
INCONEL718INCONEL Alloy 82
MONEL400
Ecodal_608AlMgSi-Wire-AlMgSiAlMgMn-Wire-AlMgSi AlMgMn-Wire-AlMgMn
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Description of geometryof component - CAD
Method of Finite Elements
FEMDivide in Finte Elements
Meshing
WeldingDefinition of heat source
Material Material properties
Boundary ConditionsHeat transfer
ClampsLoads
Setup of Welding Simulation
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Calibration of heat source according to microsection
Automatic calibration of heat source according to estimated weld pool and imposed energy per unit length of weldwith SYSWELD
Heat Source
The evaluation of heat input is not simulated. The equivalent heat source is the thermal load input for welding simualtion and has to cover all physical effects around the weld pool.
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Investigations in the evolution of residual stresses
New 3D-calculations of residual stressis consistent with measured results of the IIW round robin programme
Dr.-Ing. Tobias LooseDipl.-Ing. Jens SakkiettibutraProf. Dr.-Ing. Helmut Wohlfahrt
Specimem made of steel 316L
Validation
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The plastic material behaviour of austenitic steels at room temperature can be described by a combination of isotropic and kinematic hardening in equal percentages [5].
The influence of the Bauschinger effect decreases for plastic deformations of austenitic steels under elevated temperatures (e.g. 480 °C) [6].
5] T. Manninen et al.: “Large-strain Bauschinger effect in austenitic stainless steel sheet”, Materials Science and Engineering A 499 (2009) pp. 333-336.[6] M.C. Mataya and M.J. Carr: “The Bauschinger Effect in a Nitrogen-strengthened Austenitic Stainless Steel”, Materials Science and Engineering 57(1983) pp. 205-222.
Bauschinger effect
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Longitudinal residual stresses
-200
-100
0
100
200
300
400
500
-100 -80 -60 -40 -20 0 20 40 60 80 100
distance to weld center [mm]
resi
dual
stre
sses
[MPa
]
measured stresses at 128 mmdistance to the end of the weldseam
measured stresses at 116.5 mmdistance to the end of the weldseam
measured stresses at 106 mmdistance to the end of the weldseam
with isotropic hardeningcalculated stresses at 90 mmdistance to the end of the weldseam
Transversal residual stresses
-100
-50
0
50
100
150
200
-100 -75 -50 -25 0 25 50 75 100
distance to weld center [mm]
resi
dual
str
esse
s [M
Pa]
with isotropic hardening calculatedstresses at 90 mm distance to theend of the weld seammeasured stresses at 128 mmdistance to the end of the weld seam
measured stresses at 116.5 mmdistance to the end of the weld seam
measured stresses at 106 mmdistance to the end of the weld seam
The graphs of the with isotropic hardening calculated stresses show the typical stress peaks in the HAZ as well as the calculated.
The magnitudes of the measured and with isotropic hardening calculated peaks fit together, as well.
Comparison of measured and with isotropic hardening calculated residual stresses
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Welding direction Welding direction
Stress development
● The stress development is dependent on the geometry.● The von Mises stresses will be investigated to illustrate to different partly opposed influences
Stress distribution on the surface (isotr. hardening)
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Temperature (2. layer)
0
250
500
750
1000
1250
1500
-100 -75 -50 -25 0 25 50 75 100
distance to weld center [mm]
tem
pera
ture
[°C
]
before welding (3000 s)
max. Temperature (3269 s)
at the beginning of the coolingphase (3301 s)
Yield strength (2. layer)
0,000
50,000
100,000
150,000
200,000
250,000
300,000
-100 -75 -50 -25 0 25 50 75 100
distance to weld center [mm]
yiel
d st
reng
th [M
Pa]
3000 s (before welding)
3269 s (max. Temperature)
3301 s (at the beginning ofthe cooling phase)15000 s (after cooling)
Stress development
The magnitudes of the measured and with isotropic hardening calculated peaks fit together, as well.
The magnitudes of the measured and with isotropic hardening calculated peaks fit together, as well.
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Stress development
Von Mises stresses (2. layer)
0
100
200
300
400
500
-100 -75 -50 -25 0 25 50 75 100
distance to weld center [mm]
stre
sses
[MPa
]
before welding (3000 s)
max. Temperature (3269)
at the beginning of thecooling phase (3301 s)after cooling (15000 s)The von Mises stresses are limited
by the temperature and hardening dependent yield strength.
Reach a maximum in the work hardened HAZ
Work hardening during heating occurs as a consequence of plastic deformation where the highest stresses and the lowest yield strength values are, that is in the HAZ.
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Stress development
Longitudinal stresses occur- in the HAZ due to its extension during heating and its shrinkage during cooling. They can reach magnitudes higher than the original yield strength due to work hardening in the HAZ, - in the weld due to the hindered shrinkage of the pool.
Transversal stresses occur- due the same reasons as longitudinal stresses, - but have lower magnitudes than the longitudinal stresses due to a lower restraint in the transverse direction.
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S355E = 5,83 kJ/cmv = 1,66 mm/s
Validation of calculated residual stresses (low alloyed steel: S355)
Test: Dr. Nitschke-Pagel, Simulation: Dr. Loose
Measured distortion: w = 0,34 mmCalculated distortion: w = 0,32 mm
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Temperaturfield
Microsection SimulationS355
E = 5,8 kJ/cm
v = 1,66 mm/s
nopre heating
t = 9,2 mm
1 Weld
Bead on plate – Dr. Nitschke-Pagel (1985)
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Bead on plate – Dr. Nitschke-Pagel (1985)
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S355
E = 5,8 kJ/cm
v = 1,66 mm/s
nopre heating
t = 9,2 mm
1 Weld
Bead on plate – Dr. Nitschke-Pagel (1985)
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Span
nung
in N
/mm
²
Pre heating 300°C
S355
E = 5,8 kJ/cm
v = 1,66 mm/s
pre heating
300 °C
t = 9,2 mm
1 Weld
Bead on plate – Dr. Nitschke-Pagel (1985)
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Microstructure after welding
S235 S355
Ferrit- Perlit
Bainit
Martensit
Ferrit- Perlit
Bainit
Martensit
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S235 S355
Abhängig von Gefüge und von der Verfestigung
Yield stress after welding
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T-Joint – Sakkiettibutra (2007)
Temperature field
simulation and reality
Weld pool
HAZSimulation with consideration of
Tack weldsFiller material
Contact
Longitudinal stress - evolution
Transversal stress - evolution
For Welding simulation I use
SYSWELD Solver because:
• all important physical effects are taken into account• calculation of microstructure and hardness is possible• validable and good results• easy material data managment• available data for mainly important Materials• no limitation on geometry• no limitation on weld process • DMP-solver alvailable to manage large models• easy setup of project files
