w w w . a u t o s t e e l . o r g

Great Designs in Steel is Sponsored by:

Use your web-enabled device to download the presentations from today’s event

PRESENTATIONS WILL AVAILABLE MAY 3

w w w . a u t o s t e e l . o r g

Prediction of AHSS’s Behavior

for Non-Linear Strain Path

Thomas B. Stoughton

General Motors Company

w w w . a u t o s t e e l . o r g

A-SP 7001: Nonlinear Strain Path Project

ASP Project Team Members JPC Project Mentor

• David Anderson - AISI

Project Manager

• Eric McCarty

OEM’s

• Chrysler Chang Du, D.J. Zhou

• Ford Evanlgelos Liasi, Cedric Xia, Danielle Zeng

• GM Gene Hsiung, Tom Stoughton , Siguang Xu, John Carsley

Steel Companies

• AK Steel Raghavan Kavesary

• ArcelorMittal Gang Huang, Min Kuo, Isadora van Riemsdijk

• Severstal, NA Yu-wei Wang, Tony Chang , Steven Sheng

• Thyssenkrupp Lay Knoerr, Nivet Sever

• USS Ming Chen, Ming F. Shi

Financial

• Carolyn Philpott

Admininstration

• Terry Cullum

Colloborators and Contractors

• LSTC Li Zhang, Xinhai Zhu

• MIT Dirk Mohr, Tom Wierzbicki

• NIST Tim Foecke, Mark Iadicola

• Oakland U Xu Chen, Renjie She, Xin Xie, Lianxiang Yang

w w w . a u t o s t e e l . o r g

Outline

• Motivation

• Project Scope

• Test Methods

• Benefits of Digital Image Correlation

• Results

• Next Step

w w w . a u t o s t e e l . o r g

Importance of Improved Material Models for AHSS

Margin for error is smaller for AHSS

w w w . a u t o s t e e l . o r g

Nonlinear Strain Path Effects on Necking Limits

UNRELIABLE

IMPRACTICAL Need Advanced Necking Criteria

for Nonlinear

Deformations

w w w . a u t o s t e e l . o r g

Need for Improved Fracture Model

Current Challenges

Manufacturing Lower ductility materials give rise to

unprecedented fractures without necking,

in bending (neck suppression), at trim edges

(defects), and pure shear (s2~=-s1).

Crash Performance Accounting for manufacturing process on

product performance to reduce reliance on

physical tests requires a realistic fracture model.

Prior Needs

Manufacturing Necking dominates… so that fracture after

necking is no problem if necking is avoided.

Crash Performance Calibration of simple model is sufficient.

w w w . a u t o s t e e l . o r g

Nonlinear Strain Path Effects on Constitutive Model

Work hardening appears to be

isotropic under linear strain paths

70/30 Brass

-250

-200

-150

-100

-50

0

50

100

150

200

250

-250 -200 -150 -100 -50 0 50 100 150 200 250

Yield Work Contour0.002 0.0050.010 0.0200.030 0.0500.070 0.100

Yield surface distortion and transient

hardening effects appear under

nonlinear strain paths

70/30 Brass

30% Uniaxial

-600

-400

-200

0

200

400

600

-600 -400 -200 0 200 400 600

Yield Work Contour

0.302 0.310

0.350 0.400

Impacts Springback Prediction and Stress Formability Analysis

w w w . a u t o s t e e l . o r g

Nonlinear Strain Path Project Scope

Testing

Thin-walled Tube Tests Tokyo University of Agriculture and Technology

Bilinear Sheet Tests Oakland University

Biaxial Cruciform Tests National Institute of Standards and Technology

Model Development

Constitutive Model Massachusetts Institute of Technology,

Central Florida University

Necking Model Validation Wayne State University, Oakland University

Fracture Model Massachusetts Institute of Technology

w w w . a u t o s t e e l . o r g

Thin-Walled Tube Tests

Direct Measurement of STRESS and Strain

Actual Strain Paths and Prestrain Levels

involved in the test are shown here

Closed Loop Control of Strain Path

Homogeneous stress and strain up to 35% strain

Exceptional Model Validation Capability

Drawbacks

Expensive limited study to DDQ

Requires bending and welding of sheet material

Invalid beyond end of homogeneous deformation

w w w . a u t o s t e e l . o r g

Bilinear Uniaxial Tension Tests

•6 Steel Grades: DDQ, BH210, DP600, DP780, TRIP780, DP980

610 mm x 280 mm

•4 Pre-strain Conditions: Rolling, Transverse, Diagonal, Equal biaxial

•Pre-strain Levels: Uniaxial 0%, 5%, 10%, 15%, 20%;

Equal biaxial: 5%, 10% 280m

m (

11”)

Rolling Direction; 610mm (24”)

R-0

R-15

R-30 R-45

R-60

R-75

0

R-90

RD

TDD45

D135

280m

m (

11”)

Rolling Direction; 610mm (24”)

R-0

R-15

R-30 R-45

R-60

R-75

0

R-90

RD

TDD45

D135

RD

TDD45

D135

•7 Subsequent Tensile Orientations 00, 150, 300, 450, 600, 750, 900.

w w w . a u t o s t e e l . o r g

Limitations of Conventional Test Methods

Extensometer Measurement of Strains

0

50

100

150

200

250

300

0.000 0.100 0.200 0.300 0.400 0.500

Engineering Strain

Engineering Stress

Engineering Stress

Proportional Limit

0.2% Offset Yield

Uniform Elongation Limit

Onset of Max Axial Stress

Completion of Max Axial Stress

Last Recorded Load

Loss of Strain Uniformity Valid Strain

Measurement

Measurable Material Properties

Elastic Parameters

Proportional Limit

0.2% Offset Yield Stress

Uniform Elongation (U.E.)

Tensile Strength

R Value up to U.E.

Hardening Behavior up to U.E.

Non-Measurable Material Properties

R Value beyond U.E.

Hardening Behavior beyond U.E.

Necking Limit Strain

Fracture Limit Strain

w w w . a u t o s t e e l . o r g

Limitations of Conventional Test Methods

Extensometer Measurement of Strains

0

50

100

150

200

250

300

0.000 0.100 0.200 0.300 0.400 0.500

Engineering Strain

Engineering Stress

Engineering Stress

Proportional Limit

0.2% Offset Yield

Uniform Elongation Limit

Onset of Max Axial Stress

Completion of Max Axial Stress

Last Recorded Load

Loss of Strain

Uniformity Valid Strain

Measurement

DDQ along Rolling (R)

Direction

Non-Measurable Material Properties

R Value beyond U.E.

Hardening Behavior beyond U.E.

Necking Limit Strain

Fracture Limit Strain

Along Rolling

after 15% strain

along Rolling Direction

Unmeasureable Behavior

0

50

100

150

200

250

300

350

400

0.000 0.050 0.100 0.150 0.200

Engineering Strain

Engineering Stress

Engineering Stress

Proportional Limit

0.2% Offset Yield

Uniform Elongation Limit

Onset of Max Axial Stress

Completion of Max Axial Stress

Last Recorded Load

Unmeasureable Behavior

Along Transverse

after 15% strain

along Rolling Direction

w w w . a u t o s t e e l . o r g

Strain Measurement by DIC

Digital Image Correlation

50 mm

10 mm

DIC Point Locations 4 Point Virtual

Extensometer

0

50

100

150

200

250

300

0.000 0.100 0.200 0.300 0.400 0.500

Engineering Strain

Engineering Stress

Engineering Stress

Proportional Limit

0.2% Offset Yield

Uniform Elongation Limit

Onset of Max Axial Stress

Completion of Max Axial Stress

Last Recorded Load

Loss of Strain

Uniformity Valid Strain

Measurement

DDQ along Rolling (R)

Direction

Diffuse

Neck

Region

DIC accurately measures local true strain

field within the diffuse neck up to fracture.

Calculate distributed load across the width

to determine the local true stress based on

local true strain across the width.

50 mm

10 mm

4 Point Virtual

Extensometer

99 Point Grid in

Diffuse Neck

w w w . a u t o s t e e l . o r g

Extension of Hardening Behavior Beyond U.E.

50 mm

10 mm

DIC Point Locations 99 Point Grid in

Diffuse Neck

4 Point Virtual

Extensometer

0

50

100

150

200

250

300

0.000 0.100 0.200 0.300 0.400 0.500

Engineering Strain

Engineering Stress

Engineering Stress

Proportional Limit

0.2% Offset Yield

Uniform Elongation Limit

Onset of Max Axial Stress

Completion of Max Axial Stress

Last Recorded Load

Loss of Strain

Uniformity Valid Strain

Measurement

DDQ along Rolling (R)

Direction

0

100

200

300

400

500

600

0.0 0.2 0.4 0.6 0.8 1.0St

ress

[MP

a]

True Plastic X Strain

True Stress

Critical Point

True Stress

Proportional Limit

0.2% Offset Yield

Onset of Max Axial Stress

Completion of Max Axial Load

Estimated Final State

Hardening Behavior beyond U.E.

Necking Limit Strain

Necking Limit Stress

Hardening range: 0.21 0.90

Necking Limit: 0.65

w w w . a u t o s t e e l . o r g

0

50

100

150

200

250

300

350

400

0.000 0.050 0.100 0.150 0.200

Engineering Strain

Engineering Stress

Engineering Stress

Proportional Limit

0.2% Offset Yield

Uniform Elongation Limit

Onset of Max Axial Stress

Completion of Max Axial Stress

Last Recorded Load

Extension of Hardening Behavior Beyond U.E.

50 mm

10 mm

DIC Point Locations 99 Point Grid in

Diffuse Neck

4 Point Virtual

Extensometer

Impact of DIC Method is

more significant for analysis

of prestrain tests

Hardening range: 0.02 0.68

Necking Limit: 0.50

Along Transverse

after 15% strain

along Rolling Direction

0

100

200

300

400

500

600

0.0 0.2 0.4 0.6 0.8 1.0

Stre

ss [M

Pa]

True Plastic X Strain

True Stress

Critical Point

True Stress

Proportional Limit

0.2% Offset Yield

Onset of Max Axial Stress

Completion of Max Axial Load

Estimated Final State

Monotonic

Uniaxial

Tension

w w w . a u t o s t e e l . o r g

R Value Measurement

-0.10

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

-0.80 -0.70 -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 0.10

E11

E22

Strain History At 9 Points Across the Width at the Center of the Diffuse Neck

94

83

72

61

50

39

28

17

6

DDQ along Rolling (R) Direction

Dashed Line is the result

ONLY if the deformation is

under Uniaxial Tension with

a constant R Value

End of Linear

Behavior

End of Uniform

Elongation

Measure E11 & E22

Linear Behavior

Uniaxial Tension extends beyond U.E.

R is constant beyond U.E.

w w w . a u t o s t e e l . o r g

Determine Effect of Prestrain on R value, Yield

Stress and Hardening Behavior

•6 Steel Grades: DDQ, BH210, DP600, DP780, TRIP780, DP980

•4 Pre-strain Conditions: Rolling, Transverse, Diagonal, Equal biaxial

• Pre-strain Levels: Uniaxial 0%, 5%, 10%, 15%, 20%;

Equal biaxial: 5%, 10%

•7 Subsequent Tensile Orientations 00, 150, 300, 450, 600, 750, 900.

2

80

mm

(1

1”)

Rolling Direction; 610mm (24”)

R-0

R-15

R-30 R-45

R-60

R-75

0

R-90

RD

TDD45

D135

280

mm

(1

1”)

Rolling Direction; 610mm (24”)

R-0

R-15

R-30 R-45

R-60

R-75

0

R-90

RD

TDD45

D135

RD

TDD45

D135

w w w . a u t o s t e e l . o r g

Prestrain Effect on Yield Stress Behavior : DDQ

Rolling Diagonal Transverse Equal-biaxial

Isotropic

Isotropic Hardening in Parallel Direction of Prestrain

Enhanced Hardening in Diagonal Direction of Prestrain Reduced Hardening in Cross Direction of Prestrain

Enhanced Anisotropy

As-Received

w w w . a u t o s t e e l . o r g

Prestrain Effect on Yield Stress Behavior : DP980

Rolling Diagonal Transverse Equal-biaxial

Isotropic

Isotropic Hardening in Parallel Direction of Prestrain

Reduced Hardening in Diagonal Direction of Prestrain No Hardening in Cross Direction of Prestrain

Enhanced Anisotropy

Tests not done

w w w . a u t o s t e e l . o r g

Prestrain Effect on Hardening Behavior : DDQ

Rolling Diagonal

Transverse Equal-biaxial

Trends

o Overshoot of initial

yield

o Transient hardening

(or softening) after

yield

o Recovery to similar

hardening rate in the

asymptotic limit

Asymptotic Limit Suggests Permanent Change

in the Shape of the Yield Function

w w w . a u t o s t e e l . o r g

Prestrain Effect on Hardening Behavior : DP980

Rolling Diagonal

Transverse Equal-biaxial

Trends

o Undershoot of initial

yield

o Transient hardening

after yield

o Recovery to similar

hardening rate in the

asymptotic limit

Asymptotic Limit Suggests Permanent Change

in the Shape of the Yield Function

Tests not done

w w w . a u t o s t e e l . o r g

Prestrain Effect on R Values: DDQ

Rolling Diagonal

Transverse Equal-biaxial

No discernible trends

w w w . a u t o s t e e l . o r g

Prestrain Effect on R Values: DP980

Rolling

Transverse Equal-biaxial

No discernible change

w w w . a u t o s t e e l . o r g

• Complete Compilation of Test Data

• Begin Constitutive Model Development/Verification

Next Step For Advanced Material Models

for Nonlinear Deformation Processes

Yield

Function

Evolution

R Value

Evolution (?)

Hardening

Law

Evolution

Constitutive Model for

Improved FE Simulation of

Nonlinear Deformation

Processes

w w w . a u t o s t e e l . o r g

Q & A

Thank

you!

w w w . a u t o s t e e l . o r g

Great Designs in Steel is Sponsored by:

Use your web-enabled device to download the presentations from today’s event

PRESENTATIONS WILL AVAILABLE MAY 3