Carel ten Horn, Henk Vegter, Janka Cafollasharefea.com › upload › 2014 › 11 › 16 › 04_tenHorn_Vegter...Carel ten Horn, Henk Vegter, Janka Cafolla. Vegter yield locus in MF

Tata Steel Slide 1Vegter yield locus in MF GenYld + CrachFEMPresentation title, change View >> Header & Footer

MATFEM conference 2014

Increased accuracy for forming and crash simulation using the Vegter yield locus

Carel ten Horn, Henk Vegter, Janka Cafolla

Tata Steel Slide 2Vegter yield locus in MF GenYld + CrachFEM

Fracture in Automotive

Need for cost reduction and fuel efficiency has lead to:

� Increased use of higher strength materials

� Increased reliance on simulations

� Increased importance of accuracy of forming, springback and crash predictions

For HSS, AHSS and UHSS:

� fracture can occur before necking

� fracture limit close to or below forming limit

� predicting fracture has become important

Fracture models have become important for accurate predictions which requires calculated stresses and strains to be accurate

Good fracture predictions require using a good plasticity model


Plasticity and fracture inextricably linked

Fracture strains only have meaning when they are viewed together with plasticity data

Example: 3 point bending

� 2 materials with same bending angle at fracture but different hardening curves

� due to difference in strain distribution, different strain level at same bending angle

� different fracture strains for same bending angle

� Therefore, fracture strains need plasticity model for proper interpretation

Bending angle

[°]

Fracture strain

[-]

CP800 86 0.53

DP800HpF 85 0.35

0

200

400

600

800

1000

1200

0 0.2 0.4 0.6 0.8

True plastic strain [-]

True stress [MPa]

CP800

DP800HpFCP-grade

DP-grade

CP-grade

DP-grade

CP-grade

DP-grade


Plasticity model – Yield locus

� Many yield locus models available:

� Hill’48, Hill’90, Barlat1996, Barlat2000, Barlat-Lian, Barlat-Lege-Brem, Dell, Bron-Besson, …

� Standard models (e.g. vonMises, Hill’48, Hill’90, Yld’89) do not always coincide with (yield locus) measurements

� Advanced models require:

� more test data (which may not always be available)

� complicated fitting routines

� Solution: Vegter yield locus

It incorporates all measured points from:

� Uniaxial test

� Plane strain test

� Shear test

� Biaxial test (stack compression or bulge test)

σ2

σ1


Parameters Vegter yield locus

� Using measured points and strain ratios, an envelope is created

� A Bezier curve connects the points

� Usually tests in 3 direction but up to 10 directions possible in MF GenYld + CrachFEM

� 17 Parameters from 9 tests:

σun(0°) σun(45°) σun(90°)

r0 r45 r90

σps(0°) σps(45°) σps(90°)

α(0°) α(45°) α(90°)

σsh(0°) σsh(45°) σsh(90°)

σbi rbi

� Parameter taken directly from tests except for α

� Second stress component of plane strain point impossible to measure; so assumption: α = 0.5 (i.e. half way between hinge points)

σun(0°)

σun(90°)

"r90"

"r0"

σps(90°)σbi

"rbi"

σps(0°)

σsh(0°)

σsh(90°)

σσσσ1

σσσσ2

αps(0°)

αps(90°)


Yield locus DX57D+Z

DX57D+Z

0°/90°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσfDX57D+Z

45°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσf


Yield locus HX220BD+Z

HX220BD+Z

0°/90°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσfHX220BD+Z

45°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσf


Yield locus HX340LAD+Z

HX340LAD+Z

0°/90°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσfHX340LAD+Z

45°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσf


Yield locus HCT980X+Z High Yield

HCT980X+Z HY

0°/90°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσf HCT980X+Z HY

45°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

Hill'48

Hill'90

Barlat2000

Vegter

Measured

σσσσ1/σσσσf

σσσσ2/σσσσf


Aurora Online

� Material data service

� Enabling high-quality support

� Representative of everyday production

� For selected automotive customers

Meeting the material data needs of our Automotive customers


Aurora Online

� Basic & Advanced properties

� Datasheet PDF-file

� Raw data Excel-file

� Raw data Text-file

� CAE R2R Forming & Crash:

� Material cards for

� PAM-STAMP / PAM-CRASH

� LS-DYNA

� Autoform

� Radioss

� Abaqus


An example: the cross-die

� Semi-industrial laboratory specimen

� Materials:

� DC04

� DP800

� All runs with MF GenYld + CrachFEM

� Same hardening curves but different yield loci:

� Hill’48 (3 parameters)

� Barlat2000 (9 parameters)

� Vegter (17 parameters)

DC04 DP800

Blank size [mm] 260x260 265x265

Thickness [mm] 1.00 1.20

Blankholder force [kN] 244 823

Height [mm] 61.5 30.2


Yield locus DC04

� Hill’48 overestimates the anisotropy and the biaxial point

� Barlat2000 much better but plane strain points do not match experiments

� Vegter takes all experimental data into account

DC04 - 0°/90°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5

σσσσ1/σσσσref

σσ σσ2/ σσ σσref

Hill'48Barlat2000VegterMeasured

DC04 - 45°

-1.5

-1

-0.5

0

0.5

1

1.5

-1.5 -1 -0.5 0 0.5 1 1.5





Results Cross-die DC04

� Major strain distribution for Barlat2000 and Vegter are closer to measurement than Hill’48

Hill’48 Barlat2000 Vegter

Measured



� Hill’48 and Barlat2000 predict (very) safe part but blank size is critical in the experiment

� Vegter model predicts necking will occur at this blank size

Cross-die DC04

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-0.7 -0.5 -0.3 -0.1 0.1 0.3

Minor strain [-]

Major strain [-]

MeasurementMeasured FLCHill'48Barlat2000Vegter



� Punch force better predicted using Barlat2000 and Vegter than using Hill’48

0

50

100

150

200

250

0 10 20 30 40 50 60

Punch displacement [mm]

Punch force [kN]

Measured

Hill'48

Barlat2000

Vegter


Yield locus DP800

� Hill’48 overestimates the anisotropy and the underestimates the biaxial point

� Barlat2000 quite close but small differences in plane strain and shear points

� Vegter takes all experimental data into account

DP800 - 0°/90°

-0.5

0

0.5

1

-0.5 0 0.5 1




DP800 - 45°

-0.5

0

0.5

1

-0.5 0 0.5 1





Results Cross-die DP800

Height 25.6 mm

� experiment: some points above FLC but no necking

� Simulation:

� Strain distribution similar for all yield loci

� Vegter predicts necking is imminent


Cross-die DP800

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2

Minor strain [-]

Major strain [-]

MeasurementMeasured FLCHill'48Barlat2000Vegter

Major strain:


Results Cross-die DP800

Height 30.2 mm

� experiment: fracture on die radius

� simulation:

� ductile shear fracture risk predicts fracture at correct location

� small differences for different yield loci


Ductile shear fracture risk:


Conclusions

� A good plasticity model is essential for good fracture predictions

� Small changes in yield locus can have large effect on results

� Vegter yield locus:

� fits experimental data

� provides better forming, crash and fracture predictions

� no complicated fitting routines needed to obtain parameters

� only available for shells

++ Very good

+ Acceptable

- Not good

-- Very bad

von Mises Hill'48 Hill'90 Barlat'91 Vegter Example

Forming steel

LC steel -- - - - ++ DC03

IF -- -- -- - ++ DX56D+Z, DC06

HSS

IF Rephos -- - + - ++ HX220YD

Bake Hardening -- - -- - ++ HX220BD

LC steel Rephos - - - - ++ HX280PD

Micro Alloyed + + + + ++ HX340LAD

AHSS

Dual Phase + - - - ++ DP600, DP800

Complex Phase + + + + ++ CP800

Aluminium -- -- - -- ++ AA5182, AA6016


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Carel ten Horn, Henk Vegter, Janka Cafollasharefea.com › upload › 2014 › 11 › 16 › 04_tenHorn_Vegter...Carel ten Horn, Henk Vegter, Janka Cafolla. Vegter yield locus in MF