20 flange shear affected zone study
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Transcript of 20 flange shear affected zone study
Flange Shear Affected Zone Study
Ken SchmidGeneral Motors Corp.
Auto Steel
Partnership
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General Motors Corp.
Xin Wu, Ph.D.Wayne State University
Acknowledgements
• Wayne State University
• General Motors Corp.
• Chrysler LLC
• Ford Motor Company
• Former Ronart
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• Former Ronart
• United States Steel Corp.
• Arcelor Mittal
• Nucor Steel
• Severstal N.A.
• AK Steel Corp.
Edge Fracture with DP Materials
Challenges:
• AHSS is sensitive to edge cracking.
Mechanical trimming changes the edge
microstructures and properties, which affects
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microstructures and properties, which affects
fracture during flanging, or stretch drawing.
• Predicting fracture is difficult.
Edge Fracture with AHSS
FEA Predicted
Actual Edge Cracking
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• Conventional FEA often fail to predict edge fracture based on FLC;
• FEA procedure and failure criterion need to be improved.
Severity of Fracture
HSLA
DP980
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Die trimmed blank had severe splittingLaser Trimmed blank had no splits
Task and Objective
Task
• Characterize the shear-affected zone after
mechanical trimming and after flanging, for
three DP steels and with various flanging
length.
Objective
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Objective
• Provide an experimental foundation for
understanding the edge deformation and
fracture during trimming & flanging
• 2 parts: round-hole & multi-shaped
• 3 materials: DP600, DP780, DP980
• 3 flange lengths: 1mm, 3mm, 5mm
• 2 die clearances: 10%t, 15%t
• 2 trimming methods (mechanical & laser trimming)
Trimming & Flanging Experiments
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Round HoleMulti-shaped Hole
Various corner radii
Rollover
Burnish
Fracture
Rollover
Burnish
Fracture
Burr
Rollover
Burnish
Fracture
Burr
Sheared Edge: Four Zones
HSLA
Image provided by USS
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AHSSRollover
Burnish
Fracture
Burr
Reduced
Rollover
Burnish
Burr
Enlarged
Fracture zone
Image provided by USS
Edge Characterization 1:
Obtain Four Edge Zone Heights
Methods used:
• OM
• SEM
• Replica
Direct Observation with Optical Microscopy (OM)
Back light
Artificial notch
Sample on a magnet
holdert0
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Front light
Reflected light
Image
on the focus plane Roll-over
Burnish
Fracture
Sheared edge
Burr
Image Process and Zone Height Calculation
Roll-over Zone
Burnish Zone
Fracture Zone
Burr Zone
t0
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Procedure:
• Obtain edge image
• Trace edge
boundaries
• Fill-in colors
• Obtain Mean and
Std. Deviation over a
few thousand points
along the edgeUser software (Matlab):
scan pixels & calculate zone heights
Factors affecting edge profiles
y = -0.106x2 + 0.0771x + 0.7227
y = 0.1071x2 - 0.0848x + 0.2039
0%
20%
40%
60%
80%
100%
Rela
tive Z
on
e H
eig
ht,
%t
(a)
Fracture Burnish
Roll-over Relative
y = 0.0125x2 + 0.0164x + 0.2336
y = -0.0167x2 + 0.0039x + 0.6909
0%
20%
40%
60%
80%
100%
Rela
tive Z
on
e H
eig
ht,
%t
(b)
Fracture Burnish
Roll-over Relative
y = -0.0144x + 0.6811
y = 0.0099x + 0.2456
0%
20%
40%
60%
80%
100%
Rela
tive Z
on
e H
eig
ht,
%t
(c)
Fracture Burnish
Roll-over Relative
Die Clearance RD vs. TDMaterial Strength
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y = -0.0011x2 + 0.0077x + 0.0734
y = 0.0032x2 + 0.0046x + 0.0098
0%
5%
10%
15%
-1.5 -1 -0.5 0 0.5 1 1.55%t 10%t 15%t
Relative Die Clearance
0%
-1.5 -1 -0.5 0 0.5 1 1.5
y = 0.0042x2 - 0.0203x + 0.0755
y = -0.0044x2 - 0.0014x + 0.0156
0%
5%
10%
15%
-1.5 -1 -0.5 0 0.5 1 1.5
600 780 980
Material Strength, MPa
0%
-1.5 -1 -0.5 0 0.5 1 1.5
y = 0.0045x + 0.0733
y = 0.0023x + 0.0116
0%
5%
10%
15%
-1.5 -1 -0.5 0 0.5 1 1.5
RD TD
Shear Direction to RD
0%
-1.5 -1 -0.5 0 0.5 1 1.5
)(2
1)(''
''1
12
1
12
12
0xx
xxxx
xx
xxxx −
−+−=−
−
−+=
Edge Characterization 2: Obtain Edge Pre-Strain Distribution
00 ≈∂
∂⇒≈
y
wu
∂
∂
∂
∂+
∂
∂+
∂
∂=
j
k
i
k
j
i
i
j
ijx
u
x
u
x
u
x
uE
2
1
α2
2
tan5.02
1=
∂
∂=
x
wExx
αtan5.02
1=
∂
∂=
x
wExz
αααα
αααα
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0.01
0.1
1
10
100
0 30 60 90
Tilting Angle (deg)
Str
ain
s
Exx
Exz
Eeff
2 ∂x
= ijijeff EEE3
2
αααα
z (
mic
ron)
800
1000
1200
1400
1600
z (
mic
ron)
800
1000
1200
1400
1600
40
50
60
Effective Strain
z (
mic
ron)
800
1000
1200
1400
1600
2
2.5
3
3.5
4
4.5
Measured Shear Angle and
Converted Strain Distribution
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• Example: DP980-15%-RD
x (micron)
z (
mic
ron)
0 5000
200
400
600
x (micron)
z (
mic
ron)
0 5000
200
400
600
10
20
30
x (micron)z (
mic
ron)
0 5000
200
400
600
0.5
1
1.5
2
Localiz
ed N
eckin
g
Crack-microstructure interaction:
Diffu
se N
eckin
g
Necking control Fracture controlNecking control Fracture control
Decreasing Length Scale of Process Zone
Forming Limit
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Localiz
ed N
eckin
g
Crack-microstructure interaction:
Diffu
se N
eckin
g
>10mm(Stamping part)
1-10mm
Edge crack/roughness: 1-100 µm
Cluster of martensite: 10-100 µm
Grain/phase particle: 1-10µµµµm
Dislocation clusters: 1nm-0.1µm
Precipitates: 1-100nm
GB/Interface: 0.1-1nm
Lattice constant of Fe: 0.287nm
Great challenge to predict fracture controlled forming limitGreat challenge to predict fracture controlled forming limit
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Tru
e S
train
Eeff
Ex
Exz
Ez
Ey
Eeff,o
Ex,o
Exz,o
Ez,o
Ey,o
(a) Top/Edge Element
Hole
Piercing
Hole
Expansion
0.4
0.6
0.8
Ho
op
(M
ajo
r) S
train
, E
y
With Pre-Strain
(Switch Axes)
Without Pre-Strain
FLC
Hole Expansion
at Top-Edge of the Hole
FEA: with & without Edge Pre-strain
Hole Piercing Hole Expansion
No pre-strain
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-1.5
0 10 20 30
FEA Increment
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 10 20 30
FEA Increment
Tru
e S
train
(b) 0.4t From Top/Edge Element
Hole
Piercing
Hole
Expansion
-0.4
-0.2
0.0
0.2
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8
Radial (Minor) Strain, Ex
Hole Piercing
Piercing + Expansion
Piercing + Expansion (switch axes)
Expansion without Pre-Strain
Measure FLC for DP780
With Pre-Strain
from Piercing
Piercing
M. Chen, C. Du, X. Wu, S Liu, X. Zhu, SD Liu, IDDRG 2009
1. Obtain constituents’ distribution patterns and properties:
– Properties of individual constituents
– Micro structural distribution parameters and patterns
– Edge defect/damage parameters
2. Microstructure representation: constituents’ properties:
Meso-Scale
BridgeMicro-mechanics Continuum mechanics
A Microstructure-Based Stochastic Model
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2. Microstructure representation: constituents’ properties:
– Define meshes (scales): The element (ferrite or martensite) is
the smelliest constituent volume
– Re-construct microstructures in critical region
3. Computing with conventional FEA procedure.
– Structural instability and localized necking at small scale (no
limit strain)
– Fracture in matrix, reinforcement, or at interface
400
600
800
1000
1200
1400
Tu
e S
tre
ss
(M
Pa
)
DP600-0 DP600-45 DP600-90
DP600
DP780
DP980
Tensile Test
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Grade
YS
(MPa)
UTS
(MPa)
UE
(%)
TE
(%)n-value r-value
DP600 367 611 16.5 25.3 0.18 1.04
DP780 496 830 11.9 18.2 0.12 1.07
DP980 608 1064 7.7 12.5 0.09 1.10
0
200
0 5 10 15 20 25 30
True Strain (%)
DP600-0 DP600-45 DP600-90
DP780-0 DP780-45 DP780-90
DP980-0 DP980-45 DP980-90
Optical Micrographs
DP600
RD
t
RD
TD
TD
tSide View Top View Front View
Martensite:
13.7%
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DP780
DP980
35.0%
47.3%
22
.8m
m
USAMPA/SP’08 Tensile Behavior & Model Calibration
200
400
600
800
1000
1200
En
g. S
tre
ss
(M
Pa
)
Simulation
Exp'l
YS n-value
Martensite 620 MPa 0.19
0
500
1000
1500
2000
2500
3000
0.0 1.0 2.0 3.0
True Strain
Tru
e S
tre
ss
(M
Pa
)
Martensite
Ferrite
[1] W. N. Liu, K. S.
Choi, X. Sun, M. A.
Khaleel, Y. Ren, N.
Jia, and Y. Wang,
SAE 2008-01-1114.
Fitted
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6.35mm
22
.8m
m
Thickness 1.0mm, Element size : 0.1mm × 0.1mmTotal element #: 14,592, Dynamic Explicit
YSM : YSF 1.22, 3.33, 3.92
N-Element 14592, 4,608, 1480, 912
M-v%, measured 16v%/25v%/46v%
FEA algorithm Explicit (CPS4R, S4R)
Process Tensile, Piercing, Flanging
Ferrite
Martensite
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Eng. Strain
Exp'l Ferrite 510 MPa 0.12
Parametric Study:
Necking Evolution vs. Effective Strain
DP980
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0 5% 8% 10% 11.3% 11.7% 12.5%
Unified Model: Variable Martensite vol%
0
200
400
600
800
1000
1200
0.00 0.05 0.10 0.15 0.20 0.25
Eng. Strain
Eng. S
tress (
MP
a)
Exp. DP600
Calib. DP600
0
200
400
600
800
1000
1200
0 0.05 0.1 0.15 0.2 0.25
Eng. Strain
Eng. S
tress (
MP
a)
Exp. DP780
Calib. DP7800
200
400
600
800
1000
1200
0 0.05 0.1 0.15 0.2 0.25
Eng. Strain
En
g.
Str
es
s (
MP
a)
Exp. DP980
Calib. DP980
DP980 DP780 DP600
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Stochastic Microstructure Reconstruction
2
0Err f f + = − → ∑ %
DP780DP780
• Two-point probability function for M-particle spacing + Lineal-path probability
function for M-particle connectivity
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,0
i i REV
n
Err f f + = − → ∑ %
Total n pixels
Predicted elongation to failure:
• TD < RD;
• Segregated < Random
The effects of Martensite size and
preferred orientation are predicted
without introducing material property
assumption.
Bi-Mat’lBi-Material Model
Von Mises Strain: Bi-Mat’l vs. Monolithic
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Monolithic
Bi-Material Model
Equivalent Strain: Initial and FinalDP 600 DP780 DP980
1-mm
3-mm
5-mm
Implementation to Stamping
(Flanging)
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Pierced hole ID=10.8mm, Punch OD=18mm, Die ID=21.52mm, Fillet Radius = 3.0mm, Bland OD=70mm, Thickness=1.66mm.
1-mm
3-mm
5-mm
Summary
1. Trimmed edges were characterize by (3x3x2) Design of Experiment
The sensitivity of these effects needs to be further quantified.
With decreasing:
•die clearance,
•material strength,
•trim line angle to RD
Roll-over zone height decrease (less clear)
Burnish zone height increase
Fracture zone height decreases
Burr height reduces
More edge strain hardening and less defects;
Reduce tendency of edge cracking
w w w . a u t o s t e e l . o r gw w w . a u t o s t e e l . o r gw w w . a u t o s t e e l . o r gw w w . a u t o s t e e l . o r g
The sensitivity of these effects needs to be further quantified.
2. Strain distribution in trimmed edge zone is measured based on metal
flow line tilting angle and finite strain formulation
3. Edge fracture modeling capability can be improved by
– FEA with homogeneous properties but consider shear-induced
pre-strain
– A microstructure-based meso-scale composite model using
constituents’ properties and distribution patterns (new)