Material characterisation for accurate simulation of new ... · New materials, new process, new forming conditions so new material characterisation need for simulation feeding. Innovative

SIXTH FRAMEWORK PROGRAMME PRIORITY [6.2] [SUSTAINABLE SURFACE TRANSPORT]012497 DEVELOPMENT OF BEST PRACTICES AND IDENTIFICATION OF BREAKTHROUGHTECHNOLOGIES IN AUTOMOTIVE ENGINEERING SIMULATION - AUTOSIM

Summary

Material characterisation for accurate simulation of new sheet metal forming processes

Marian Gutierrez, LABEIN Tecnalia

A general overview of the problems/issues/state of the art/research related with material characterisation that appear in the development of innovative sheet metal forming processesFour examples briefly highlight some of these points

Magpulse Technologies

1


OverviewIntroduction:

New materials, new process, new forming conditions so new material characterisation need for simulation feeding

Innovative forming process:• High speed forming:

– Electromagnetic and electrohidraulic forming– Material characterisation at high strain rates

• Hydroforming– Sheet / tube characterisation

• Hot/Warm metal forming: Hot stamping, Hot Metal Gas Forming (HMGF), hot/warm hydroforming,

– Temperature dependent material characterisation • Austenitic steel forming:

– Modelling of TRIP effect Conclusions


2


Introduction: New materials in automotive

1.- Less formability

2.- More springback

3.- More stresses required


3


Introduction: New forming processes

Hydroforming

High speed forming

Pre-Form Geometry Electromagnetically Formed

Hot / Warm forming


4


Introduction: Conventional sheet forming simulation

Failure detectionThickness distributionLoad press

PROCESS parameters: Operation sequence, pressure, axial feeding, press velocity

GEOMETRICAL data:Sheet dimensionsTool geometry

MATERIAL data:Curve strain-stress

TRIBOLOGICAL data:Friction coefficient (lubricant)

FEA FORMING SIMULATION


5


Introduction: Conventional materials characterisation

Engineering stress-strain curve

Uniaxial tensile test

- Temperature ?- Tube ?- Strain rate ?- …

Forming limit diagram (FLD)

Nakazima test

New process conditions

A unification of the standard for FLD testing is being investigated within IDDRG


6


Introduction: New materials characterisation

ε

Springback

• Springback• Welding line characterisation• Friction characterisation• Microestructure evolution during forming process

Tower Automotive Congreso 2002 New Developpments in sheet Metal forming

Strip drawing test

New material variables


7


High speed forming: Basic conceptElectrohidraulic Forming (EHF)

Store energytrasmision

Kinetic energy

ElectromagneticForming EMF

ElectrohidraulicForming EHF

Rogowski Probe

Ring Specimen

Charging Circuit

Capacitor

Solenoid

Electromagnetic Forming (EMF)

Bridge wire

Die

To vacuum

water

sample

Capacitor bank


8


High speed forming: Main Properties

• High speed deformation of material, confined inertially allows high deformation • Mechanics and physics of the high velocity process are quite different than quasi static• Forming event takes place in several tens of MICROSECONDS• Hence, achieved forces launch the material rapidly• High strain rates higher than 1000 sec-1 • Formability increase by uniform elongation in all regions of blank• High achievable pressures Embossing, coining purposes • Wrinkling tendency diminished.• No Springback


9


High speed forming simulation

Coil and sheet/tube Primary & InducedCurrents

Force exerted in the piece

0

50000

100000

150000

200000

250000

300000

350000

400000

0 0,000005 0,00001 0,000015 0,00002

Time (seconds)

Forc

e (N

ewto

n)Force actingon flat sheet

Forming Analysis: Evolution during

Forming

MagneticAnalysis:force profileduring time interval defined by transient pulse.

Loosely Coupled Approach


10


High speed forming: Flow curve at different strain rates

International Iron and Steel Institute


11


High speed forming: Uniaxial test methods

Courtesy: International Iron and Steel Institute


12


High speed forming: Formability

Courtesy:Ohio Univ

Die

Outlet to Vacuum pump

Fixture

9.5 mm

Die

Outlet to Vacuum pump

Fixture

9.5 mm9.5 mm

0

10

20

30

40

50

-40 -20 0 20 40

Minor strain (Engg %)

Maj

or st

rain

(Eng

g %

)

v1-soft lead-541v1-hollow end-352v1-round end-147v1-polymer-776


13


Hydroforming: Hydrotest

Labein (Spain)CSM (Italy)SIMR (Sweden)Ptu (Germany)Act (Spain)Salzgitter (Germany)Rautaruukki (Finland)

“Investigation of the influence of the pre-hydroforming processes and development of characterization methods for the testing of steel semi-

products for hydroforming”RFCS project 7210-PR-372 (2002 – 2005)

A major obstacle in hydroforming of steel semiproduct is the lack of an unified test method for determining

their hydro-formability


14


Hydroforming: Hydrotest project objectives

Development of an unified test method and guidelines needed

Improve the simulation and characterization of hydroformingsteel components

Semi-product

Code GradeDelivery condition Coating Semi-product manufacturing

M1 S235 +CR2 none welded and cold sizedM2 S235 +CR2 galvanized welded and cold sizedM3 H260 I +CR2 none welded and cold sizedM4 H360LA +CR2 none welded and cold sizedM5 H340X *) +CR2 galvanized welded and cold sizedM6 H340X *) +CR2 galvanized long blank + laser weldM7 H340X *) +CR2 galvanized trans blank + laser weldM8 H340X *) +CR2 galvanized welded and cold sizedM9 H340X *) +CR2 galvanized long blank + laser weldM10 H340X *) +CR2 galvanized trans blank + laser weldM11 S235JR +CR2 none welded and cold sizedM12 S235JR NBK none welded and cold sizedM13 S355 MC +CR2 none welded and cold sizedM14 S355 MC +CR2 none long blank + laser weldM15 27MNCRB5 NBK none welded and cold sized

Flow material curve (stress-strain curve)

FLD determination

Welding line characterization

Friction characterization

Geometry properties (thickness distribution on tube)


15


Hydroforming: Flow curve determination

Flow curve (strain-stress)

Flow curve approximation from free bulge test with fixed ends and comparison for conventional tensile test (PtU)

-Conventional tensile test-Whole longitudinal tensile test-Tensile test on samples from tube-From busting test


16


Hydroforming: Flow curve determination

Material characterisation (stress-strain curve)

Tensile test

Sheet Whole tube Strip from tube From bursting test (fixed end)

Results Tensile curves in all directions

Tensile curves in longitudinal direction

Tensile curve in longitudinal and

transversal direction

Bursting and maximum pressure. Maximum circumferencial expansion (one point measurement).

Stress-strain curve

Application Input for FEM Input for FEM Input for FEM Tube (hydro)formability limit in expansion with low,

unspecified self feeding. One point in the FLD, close to plane strain.

Hydroforming suitability

In the current tests all three tensile test methods show similar results. Given the cost/time factor, the tensile tests could be

performed on sheet with adequate results.

Concerning flow curves similar results than tensile test but longer curves (more expansion). Deformation

mode close to real hydroforming one

Cost and time for testing + +++ ++

++ Cheap and easy to perfom. Up to 2 tubes per hour can

be tested

FEM sensibility All burst tests are considered as limits to the

formability and are compared with FE analysis results.

Other remarks The only FLD point is plane strain. Easy way to give a

general classification of the hydroformability of the tube.


17


Hydroforming: FLD determination

Tube Nakazima Test (Kimab, Sweden)

Sheet Nakazima Test (Labein, Spain)Forming limit curve (FLD)

-Sheet Nakazima-Tube Nakazima-From sheet bulge test-From tube bursting test

C1 - S235 1.5 mm

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

-0,20 -0,15 -0,10 -0,05 0,00 0,05 0,10 0,15 0,20 0,25 0,30Minor strain

Maj

or s

trai

n

C1 - S235

Ell_300x300_A

Ell_300x300_B

Ell_220x300_B

FLD from bulge test (CSM, Italy)


18



minor strain ε2

maj

or s

train

ε1

deep drawinguniaxial tension

plane strain

stretc

h-dr

awing

ε1=ε2

ε1=2ε2

ε2=0

ε1=-2ε2

ε1=-ε2

0

11 ln

ll

=ε0

22 ln

ll

=ε

l0

l1

l2

free bulge test with axial

compressive feedfree bulge test with axial

tensile feed

free bulge testwith fixed ends

fixed

endsaxial

compression

axial tensileIn

itial

tube

free

ends

FLD from bursting test (PtU, Germany)


19



0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5

SIMR, d=57mm

SIMR, d=100mm

Labein, d=100

CSM burst tests

Material C11.5 mm, not galvanisedtested in rolling direction

maj

or tr

ue s

train

minor true strain0.0

0.1

0.2

0.3

0.4

0.5

0.6

-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3

M3M8

M9M10M13 minor true strain

maj

or tr

ue s

train

Sheet FLD results at KIMAB and Labeinand results of burst tests at CSM

Tube FLD results at PtU and KIMAB


20



-0.10

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

-0.10 0.00 0.10 0.20 0.30 0.40 0.50

approved pointstangential prestrainprestrained FLCcircumferential tubeapprox axial tube

axial engineering strain

tang

entia

l eng

inee

ring

stra

in Material M12 prestrained in tangential direction

-0.10

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

-0.10 0.00 0.10 0.20 0.30 0.40 0.50

Material M12 prestrain in axial tension

distance to crack >2.5 mm

tang

entia

l eng

inee

ring

stra

in

axial engineering strain

FLC for tubes prestrained circumferentially and axially (KIMAB)

Non linear strain paths during hydroforming stages


21



0

10

20

30

40

50

60

-30 -20 -10 0 10 20 30 40Minor strain

Maj

or s

train

Preform

Hydroforming

FLD LABEIN

KIMAB Diameter100KIMAB Diameter 57

KIMAB NakazimaM8TKIMAB NakazimaM9TKIMAB NakazimaM10TPTU M8

PTU M9

PTU M10

Balance between the effort in characterization and simulation improvement


22


Hydroforming: Welding line characterisation

Microtensile test samples Tensile curves on weld and base materials (CSM, Italy)

M5 - H340X 1.5mm

0

100

200

300

400

500

600

700

800

900

1000

1100

0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16True strain [ ]

True

str

ess

[Mpa

]

M5_Base3

M5_Base4

M5_Base6

M5_Welding1

M5_Welding2

M5_Welding5

C5_1_longitudinal

C5_2_longitudinal

C5_3_longitudinal

1,00

1,05

1,10

1,15

1,20

1,25

1,30

1,35

1,40

1,45

1,50

1,55

1,60

0 20 40 60 80 100 120 140 160 180 200 220 240 260

Length (mm)

Thic

knes

s (m

m)

M1_base

M1_mod1

M2_mod1

BA

A

B

C A

C

Process/FEM sensitivity to process/material variablesWhat we need for simulation


23


Hydroforming: Geometrical properties

Thickness distribution (PtU)

measure

simulateSimulation time multiply by 100

Balance between FEM complexity, CPU time required, and result quality


24


Hydroforming: Friction characterisation

Strip drawing test (Labein)

0

0,05

0,1

0,15

0,2

0,25

0 50 100 150Sliding length

Coe

ffici

ent o

f fric

tion

oil_3Tn_7,5mm/s_1oil_3Tn_7,5mm/s_2oil_3Tn_7,5mm/s_3oil_3Tn_155mm/s_1oil_3Tn_155mm/s_2oil_3Tn_155mm/s_3oil_5Tn_7,5mm/s_1oil_5Tn_7,5mm/s_2oil_5Tn_7,5mm/s_3oil_5Tn_155mm/s_1oil_5Tn_155mm/s_2oil_5Tn_155mm/s_3

Pulling cylinder

Breaking cylinder

Cylindrical toolwith radius r

BUT test (Kimab)

0,00

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,10

0 10 20 30 40 50 60 70 80 90distance [mm]

fric

tion

coef

ficen

t [ ]

M8_Oil_01M8_Oil_02M8_Oil_03M8_Oil_04M8_Oil_05

Straight tube friction test(Ptu)

• Balance between the effort in characterization and simulation improvement• Balance between FEM complexity and results quality


25


Hydroforming: Hydrotest conclusions

Property Test A Test BFrom tensile test on sheet or from tube bursting fixed ends

Tube bursting compresive axial feeding

Strip drawing or BUT

Tube bursting fixed ends

Sheet Nakazima

Circumferential wall thickness measurementTube diameter measurementLocal wall thickness measurement (weld, HAZ)

Test CMaterial characterisation (Stress-strain curve)

Formability

FLD Tube bursting. 1.force free ends 2.axial compression). Prestrain FLD

Friction Straight tube friction test

Geometry properties testing

Weld


26


Hot/Warm Forming: Processes

Sheet Hot Stamping (boron steels)Tube and sheet forming:

Warm Hydroforming with fluid(non ferrous alloys, Al, Mg) 400ºC

Hot Metal Gas Forming, HMGF (ferrous and non ferrous alloys) (Tª >800ºC)

Volvo XC90 Boron steelcomponents(source ArcelorAuto)


27


Hot/Warm Forming: FEM simulation consideration

• At elevated temperatures the formability increase with increasing the temperature and decreasing strain rate.

• The increase in strain rate sensitivity is the dominant factor to improve the deformability.

• Influence of the heating rate and holding time

• Micro-structural evolution during forming and during the heating

• Hot stamping : isothermal process but depending on the strain rate (PamStamp, StampPack, FORGE, DEFORM, ABAQUS…)

• HGMF: Change of the temperature during the process simulation thermo-mechanical coupled and fit of

the thermic parameters (FORGE, DEFORM, ABAQUS)

Flow curves:Uniaxial test

• Material law for several strain rates and temperatures

• Forming Limit Diagram

Material Formability: Biaxial states test


28


Hot/Warm Forming: Uniaxial tests under heating conditions

• Thermal gradient in the specimen (heating system: induction coil, Joule effect)• The local strain rate is not constant• The maximum deformation is very small due to the necking, short flow curve• Dynamic recristallisation has effect on stress-strain curve.• Difficult to monitoring and control due to the temperature.• Inert atmosphere to avoid the oxidation (some steels)

Gleeble Machine (Acerinox)


29


Hot/Warm Forming: Biaxial tests under heating conditions• Thermal gradient in the sheet / tube (heating system: Joule effect) • Gas pressure curve variation during the test to obtain strain rate constant• Inverse analysis with FEM to obtain the strain rate constant• Thermic and electrical isolation with the dies• Monitor and control of process variables: temperature, pressure, electrical current (A) and

voltage (V). • Pressure system (Nitrogen)


30


Austenitic steel forming: TRIP effect“Implementation of a Non-isothermal Material Model For Austenitic Stainless Steels in Deep Drawing Simulation”(RFCS project “Methods of improving the deep drawing properties of austenitic stainless steels”-7210PR304)

Total hardening: Htot = Ha.Va + Hm.Vm

Austenite Martensite

Va, Vm = Volume fractions of the austenite and the martensite phasesHa, Hm = Hardening values

Temperature dependent

Latent heat

Phase change during plastic deformation

TRIP effect in austenitic stainless steels forming


31


Austenitic steel forming: FE simulation

Flow stress

Microstructure TemperaturePhase change latent heat

Temperature dependentphase transformation

Hea

t gen

erat

edby

mec

hani

cal w

orkM

artensite depending

hardening

Strain-inducedaust. ->

mart. transform

ation

Tem

pera

ture

depe

nden

t

hard

enin

gFlow stress

Microstructure TemperaturePhase change latent heat

Temperature dependentphase transformation

Hea

t gen

erat

edby

mec

hani

cal w

orkM

artensite depending

hardening

Strain-inducedaust. ->

mart. transform

ation

Tem

pera

ture

depe

nden

t

hard

enin

g

Material constitutive model by Hänsel et al.(15 material parameters)

Material data from non isothermal tensile tests

FE Simulation of cold forming processes with austenitic stainless steels


32


Austenitic steel forming: Non isothermal tensile tests1.4318

0102030405060708090

100

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4equ_strain

T(ºC

)

Simu_T0Exp_T0Simu_RTExp_RTSimu_T60Exp_T60Simu_T100Exp_T100

1.4318

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4equ_strain

Vm (/

1)

Simu_T0Exp_T0Exp_T0 fitted curveSimu_RTExp_RTExp_RT fitted curveSimu_T60Exp_T60Exp_T60 fitted curveSimu_T100Exp_T100Exp_T100 fitted curve

1.4318

0

200

400

600

800

1000

1200

1400

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40equ_strain

Eq_s

tres

s(M

Pa)

Simu_T0Exp_T0Exp_T0 fitted curveSimu_RTExp_RTExp_RT fitted curveSimu_T60Exp_T60Exp_T60 fitted curveSimu_T100Exp_T100Exp_T100 fitted curve

v = 0.11 mm/s

Experimental data courtesy of Outokumpu Stainless AB, Sweden

Thickness = 1 mm

Simulation results and experimental data


33


Austenitic steel forming: Deep drawingSimulation results and experimental data

SIM.

EXP.(Optical)

TRUE MAJOR STRAIN TRUE THICKNESS DECREASEExperimental data courtesy ofThyssenKrupp Nirosta, Germany


34


Austenitic steel forming: Summary

• Implementation of a non-isothermal material model for austenitic stainlesssteels in deep drawing simulation, taking into account the TRIP effect.

• The model is completed with the experimetal test need and the way to getthe model parameter for the test

• Simulation can now be used for process optimisation


35


Conclusions

• New constitutive models• Even for traditional models they is a need for data • New characterization method• Data for materials models are not available• Process/FEM sensitivity to process/material variables

• Balance between FEM complexity, CPU time required and resulsquality

• Balance between the effort in characterization and simulation improvement

• Important to know what we expected for the simulation: Balance quantitative versus qualitative results


36


Thank you for your attention

Marian Gutierrez (LABEIN – TECNALIA, Bizkaia, Spain)[email protected]


37

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Material characterisation for accurate simulation of new ... · New materials, new process, new forming conditions so new material characterisation need for simulation feeding. Innovative