PRESENTATIONS WILL AVAILABLE MAY 3 Use your web …/media/Files/Autosteel/Great Designs in...
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PRESENTATIONS WILL AVAILABLE MAY 3
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Prediction of AHSS’s Behavior
for Non-Linear Strain Path
Thomas B. Stoughton
General Motors Company
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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
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Outline
• Motivation
• Project Scope
• Test Methods
• Benefits of Digital Image Correlation
• Results
• Next Step
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Importance of Improved Material Models for AHSS
Margin for error is smaller for AHSS
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Nonlinear Strain Path Effects on Necking Limits
UNRELIABLE
IMPRACTICAL Need Advanced Necking Criteria
for Nonlinear
Deformations
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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.
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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
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Prestrain Effect on R Values: DDQ
Rolling Diagonal
Transverse Equal-biaxial
No discernible trends
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Prestrain Effect on R Values: DP980
Rolling
Transverse Equal-biaxial
No discernible change
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• 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
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Q & A
Thank
you!
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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