dept. of materials science and engineering, the ohio state university plasticity and failure of...
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Center forAdvancedMaterials andManufacturing ofAutomotiveComponents
Dept. of Materials Science and Engineering,
The Ohio State University
Plasticity and Failure of Advanced High Strength Steels
R.H. Wagoner, Ji Hyun Sung, A. Madeshia, Ji Hoon Kim
R. H. Wagoner 2
Outline
• Introduction
• Draw-Bend Testing
• Constitutive Equations
• Draw-Bend Simulations
• Conclusions
R. H. Wagoner 3
Introduction
R. H. Wagoner 444
NSF Workshop on AHSS (October 2006)E
lon
gati
on (
%)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200300 900 1600
DP, CP
TRIP
MART
HSLA
IF
Mild
IF- HS
BHCMn
ISO
Elo
nga
tion
(%
)
600
TWIPAUST. SS
L-IP
ISO
R. W. Heimbuch: An Overview of the Auto/Steel Partnership and Research Needs [1]
R. H. Wagoner 5
Unexpected Forming Failures
Stoughton, AHSS Workshop, 2006
Comparison between FE / FLD simulation and practice.
R. H. Wagoner 66
“Shear Failure?”
• FLD– Tensile localization map
(+ biaxial)
• AHSS– “Shear failure” at die
radii, minimal width or thickness strain
Mg AZ31B Al 6013 (Shear type) (Tensile localization)
Lou, XY, Int. J. Plasticity,23, 1, 2007, 84
6
R. H. Wagoner 7
Project Objectives
• Produce and characterize fractures at die radii (“shear
failure”)• Develop a new formability criterion (with bending)
Jim Fekete et al., AHSS Workshop, 2006
R. H. Wagoner 8
Approach: Draw-Bend Test
R. H. Wagoner 9
Draw-Bend Testing
R. H. Wagoner 10
Draw-Bend Fracture Testing
Sta
rt
Max. Finish
Max
. F
inis
h
V1
Start
R
317.5 mm190.5 mm
19
0.5
mm
43
5.5
mm
V2 = V1
u1 = V1 t
R: 1/8, 3/16, 1/4, 7/16, 3/4 inch (3.2, 4.8 , 6.4, 11.1, 19.1 mm)
R. H. Wagoner 11
Phenomenological Failure Types
Type I
Type II
Type III
65o
65o
V2
V1
Type I: Tensile failure (unbent region)
Type II: Shear failure (not Type I or III)
Type III: Shear failure (fracture at the roller)
R. H. Wagoner 12
• R/t = 2.27 , V1 = 2.54 mm/s, = 0.37 , ddtmax = 0.22 /s
II
I
III
Failure Types: DP590(B)-CR-1.4mm
V 2/V 1
= 0
V 2/V 1
= 0.25
V 2/V
1 =
0.5
0
Xc = 6mm
Xc = 43mm
Xc = 17mm = 0.92
= 0.89
max
max
= 0.96max
R. H. Wagoner 13
Transition: Type II III (DP590)• R/t = 2.57, V1 = 127 mm/s, m = 0.33 , ddtmax = 7.95 /s
V2/V1 = 0.25 V2/V1 = 0.20 V2/V1 = 0.10
II III III III
V2/V1 = 0.20
Xc = 24 Xc = 16Xc = 20Xc = 20
= 0.94 = 0.93 = 0.95max maxmax = 0.93max
R. H. Wagoner 14
Infrared Temperature Measurements• Tmax ~ 50 to 100oC near fracture • Type III
– Differential temperature rise along the width
R. H. Wagoner 15
IR Results - Type III
0
100
200
300
400
500
600
700
800
20
30
40
50
60
70
80
0 0.2 0.4 0.6 0.8 1
Time (sec)
Front stress
Back stress
1
2
3
4
C_ DP5902.65R/t
25.4 mmw0V2
127 mm/sV1
(Fracture)
t = - 0.07 s t = 0 s t = 0.07 s t = 0.14 s
Material V1 (mm/s)TTC (oC)
TFLIR (oC)
(emissivity) T
DP590(C)-GA-1.75mm 127 60.25 53.8 0.7 6.5
Calibration
R. H. Wagoner 16
• R/t ( m & ddtmax )IIII
• V2/V1 ( Xc )IIII
• V1 ( ddtmax )IIII
Controlled Draw-Bend Parameters
• R/t m= ln(1+tsheet/R), m=tsheet/R
• V1 max~ m/D, D~3tsheet/V1 (FEA)
• V2/V1 related to Xc at failure
Observed Role of Parameters
..
R. H. Wagoner 17
Definition of Normalized Stress
Maximum Pull Force / Original AreaMaximum Pull Force / Original Area
Ultimate Tensile Strength (at = 0.7/s)Ultimate Tensile Strength (at = 0.7/s)..
R. H. Wagoner 18
Effect of R/t (V1 = 127 mm/s, V2/V1 = 0)
6
*
1
R=
t
3
*
2
R=
t
R. H. Wagoner 19
Effect of Bend Strain Rate (V2/V1 = 0)
R. H. Wagoner 20
Failure Types (V2/V1=0)
R/t (m) V1 (mm/s)
1.7(0.46)
2.6(0.33) 3.7(0.24) 6.5(0.14) 11(0.09)
127 0.88 0.96 0.99 1.00 0.99
25 0.88 0.95 0.98 0.97 0.96
2.5 0.91 0.94 0.95 0.94 0.93
R/t (m) V1 (mm/s)
2.3(0.37) 3.4(0.26) 4.5(0.20) 7.9(0.12) 13.6(0.07)
127 0.92 0.95 0.99 0.96 0.98
25 0.92 0.98 0.98 0.95 0.96
2.5 0.94 0.97 0.97 0.93 0.94
DP590(C)-GA-1.75mm
DP590(B)-CR-1.4mm
KeyType IType IIType III
R. H. Wagoner 21
Failure Type Map (DP780, V2/V1=0)
R. H. Wagoner
22
Failure Type Map (TRIP780, V2/V1=0)
R. H. Wagoner 2323
(R/t)*1 and (R/t)*2 for D-P Steels (V2/V1=0)
V1(mm/s) 51(127) 13(25) 2.5
DP590(B)-CR-1.4 6 3 2
DP780(D)-GI-1.4 6 3 3
DP980(D)-GA-1.45 11 4 4
• Shear / Tensile Transition, (R/t)*1 [ = f (matl, V1) ]
• Maximum Stress Transition, (R/t)*2 [ not f (matl, V1) ]
V1(mm/s) 51(127) 13(25) 2.5
DP590(B)-CR-1.4 4 3 4
DP780(D)-GI-1.4 4 4 5
DP980(D)-GA-1.45 4 4 4
R. H. Wagoner 24
Constitutive Equations
R. H. Wagoner 25
)()(),( ThgTf
1D Constitutive Equation
sgm
/10,)()2 31
1
2
)]exp(1[0
BAf
Kf
Voce
nHollomon
CTTTHTh o25),(1)()1 00
CTTTwhere
ffTfo
VoceHollo
25);(:
)1(),()3
0021
R. H. Wagoner
Comparison in Tensile Range (25oC)
26
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Large-Strain Comparison (25oC)
0 84 1 797( . , . )r m
27
R. H. Wagoner 28
Thermo-Mechanical FE Simulation
• Abaqus Standard (V6.7)• 3D solid elements (C3D8RT), 2 layers
• Von Mises, isotropic hardening• Symmetric model
Tinitial = 25oC
Gage region (2% taper)
Sample
hmetal, air = 20 W/m2K
Grip
hmetal,metal = 5 kW/m2K
Grip
R. H. Wagoner 29
Simulated Tensile Test (50oC)
0 0.05 0.1 0.15 0.2 0.25 0.30
200
400
600
800
En
gin
eer
ing
Str
ess
(M
Pa)
Engineering Strain
DP590(B)-CR-1.4mm
50oCIsothermal
d/dt =10-3/s
Measured FE SimulatedVoce
FE SimulatedHollomon
FE SimulatedH/V
R. H. Wagoner 30
Predicted Ductility (ef): DP590
* ef is defined by measured fractional load drop at failure* ef is defined by measured fractional load drop at failure
Temp Exp
ef*
Hollomon Voce Mixed
25℃ 0.247 0.274(11%) 0.184(-23%) 0.229(-10%)
50℃ 0.238 0.282(15%) 0.185(-19%) 0.228(-5%)
100℃ 0.195 0.278(43%) 0.184(-4%) 0.204(5%)
Std. Dev.(%) 0.056(24%) -0.048(-15%) 0.013(7%)
R. H. Wagoner
Predicted Ductility (ef): DP 590, 780, 980
31
Hollomon Voce H/V
DP590 0.04(14%) 0.05(20%) 0.02(7%)
DP780 0.03(18%) 0.04(22%) 0.01(6%)
DP980 0.04(30%) 0.03(21%) 0.01(5%)
R. H. Wagoner
Large-Strain Comparison (DP780)
0 97 1 807( . , . )r m
32
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Large-Strain Comparison (DP980)
0 76 1 904( . , . )r m
33
R. H. Wagoner 34
Draw-Bend Simulations
(Coupled Thermo-Mechanical FEM)
Note: Test results are shown for fixed roller and lubricated condition.
R. H. Wagoner 35
FE Draw-Bend Model
hmetal,air = 20W/m2K
hmetal,metal = 5kW/m2K
= 0.08
U1, V1
U2, V2
• Abaqus Standard (V6.7)
• 3D solid elements (C3D8RT), 5 layers
• Von Mises, isotropic hardening
• Symmetric model
R. H. Wagoner 36
Role of Thermal Effects (Type III)
0
5
10
15
20
25
30
0 20 40 60 80 100
Fro
nt
Fo
rce
(k
N)
Front Displacement (mm)
DP590(B)-CR-1.4mmR/t=3.4, V
1=127mm/s, V
2/V
1=0
Solid Elem.
Measured Nonisothermalsimulation (Type III)
Isothermalsimulation (Type I)
R. H. Wagoner 37
R/t = 7.9, V1=127mm/s, V2/V1=0 (Type I)
R. H. Wagoner
R/t = 7.9, V1=127mm/s, V2/V1=0 (Type I)Temperature (oC)
F=Fmax
U1=46mmF=0.9Fmax
U1=61mm
52oC
117mm
p=0.16
Type I
99oC, p=0.41(93oC measured)
38
R. H. Wagoner 39
R/t = 7.9, V1=127mm/s, V2/V1=0 (Type I)
0
5
10
15
20
25
30
0 20 40 60 80 100
Fo
rce
(k
N)
Front Displacement (mm)
DP590(B)-CR-1.4mmR/t=7.9, V
1=127mm/s, V
2/V
1=0
Nonisothermal, Solid Elem.
Back
Front
Measured
FE Simulated
R. H. Wagoner 40
R/t = 3.4, V1=127mm/s, V2/V1=0.5 (Type II)
R. H. Wagoner
R/t = 3.4, V1=127mm/s, V2/V1=0.5 (Type II)
Temperature (oC)
F=Fmax
U1=61mmF=0.9Fmax
U1=67mm
101oC, p=0.38(93oC measured)
10mm
Type II
157oCp=0.65
41
R. H. Wagoner 42
R/t = 3.4, V1=127mm/s, V2/V1=0.5 (Type II)
0
5
10
15
20
25
30
0 20 40 60 80 100
Fo
rce
(k
N)
Front Displacement (mm)
DP590(B)-CR-1.4mmR/t=3.4, V
1=127mm/s, V
2/V
1=0.5
Nonisothermal, Solid Elem.
Measured
FE Simulated
Back
Front
R. H. Wagoner 43
R/t = 3.4, V1=127mm/s, V2/V1=0 (Type III)
R. H. Wagoner
R/t = 3.4, V1=127mm/s, V2/V1=0 (Type III)
Temperature (oC)
F=Fmax
U1=44mmF=0.9Fmax
U1=46mm
87oC, p=0.39(80oC measured)
155oCp=0.72
Type III
44
R. H. Wagoner 45
R/t = 3.4, V1=127mm/s, V2/V1=0 (Type III)
0
5
10
15
20
25
30
0 20 40 60 80 100
Fo
rce
(k
N)
Front Displacement (mm)
DP590(B)-CR-1.4mmR/t=3.4, V
1=127mm/s, V
2/V
1=0
Nonisothermal, Solid Elem.
Measured
FE Simulated
Front
Back
R. H. Wagoner
Observed vs. Simulated Failure (DP590)
R/t V1 (mm/s) 2.3 3.4 4.5 7.9 13.5
127 0.96 0.99 1.00 1.00 1.00
25 0.96 0.99 1.00 1.00 1.00
2.5 0.97 0.98 0.98 0.98 0.98
DP590(B)-CR-1.4mm Key: Type I, Type II, Type III
R/t V1 (mm/s) 2.3 3.4 4.5 7.9 13.5
127 0.86 0.93 0.96 0.99 0.99
25 0.86 0.93 0.95 0.98 0.99
2.5 0.88 0.94 0.96 0.98 0.98
V2/V1=0.5
V2/V1=0
46
R. H. Wagoner
Observed vs. Simulated Failure (DP780)
R/t V1 (mm/s) 2.3 3.4 4.5 7.9 13.5
51 0.91 0.93 0.94 0.96 0.95
13 0.90 0.92 0.93 0.94 0.94
2.5 0.91 0.93 0.94 0.94 0.94
DP780(D)-GI-1.4mm
V2/V1=0.5
Key: Type I, Type II, Type III
R/t V1 (mm/s) 2.3 3.4 4.5 7.9 13.5
51 0.83 0.87 0.91 0.93 0.94
13 0.82 0.87 0.90 0.92 0.94
2.5 0.83 0.88 0.90 0.93 0.94
V2/V1=0
47
R. H. Wagoner
Effect of R/t (DP590, V2/V1 = 0)
48
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Effect of R/t (DP780, V2/V1 = 0)
49
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Effect of Strain Rate (DP780)
50
R. H. Wagoner 51
Conclusions
Note: All test results are shown for fixed roller and lubricated condition.
R. H. Wagoner 52
Conclusions
• Thermo-mechanical simulation predicts the formability of DP590, DP780.
• Damage mechanics is not required.
• Deformation-induced heating is a critical aspect.
• New constitutive form is needed for accurate predictions.
• Knowledge of strain hardening beyond eu is critical.
R. H. Wagoner 53
Definition of Normalized Stress
0.7/sdt/dσ/AF
σmaxUTS
omax
1
• UTS (DP590(C)) = 614 MPa
• UTS (DP590(B)) = 642 MPa
• UTS (DP780(D)) = 835 MPa
• UTS (TRIP780(D)) = 875 MPa
• UTS (DP980(D)) = 1014 MPa
R. H. Wagoner 54
Failure Type Map (V2/V1=0): DP590(B)
R. H. Wagoner 55
Failure Type Map (V2/V1=0): DP780(D)
R. H. Wagoner 5656
Failure Type Map (V2/V1 = 0): DP980(D)
R. H. Wagoner 57
Failure Type Map (V2/V1=0.5): DP590(B)
R. H. Wagoner 58
Failure Type Map (V2/V1=0.5): DP780(D)
R. H. Wagoner 5959
Failure Type Map (V2/V1 = 0.5): DP980(D)
R. H. Wagoner 6060
Summary: (R/t)*1 varies with material and V1
V1(mm/s) 51(127) 13(25) 2.5
DP590(B)-CR-1.4 6 3 2
DP780(D)-GI-1.4 6 3 3
DP980(D)-GA-1.45 11 4 4
• Shear / Tensile Failure Transition, (R/t)*1: V2/V1=0
• Shear / Tensile Failure Transition, (R/t)*1: V2/V1=0.5
V1(mm/s) 51(127) 13(25) 2.5
DP590(B)-CR-1.4 14 14 6
DP780(D)-GI-1.4 14 11 6
DP980(D)-GA-1.45 13 13 11
R. H. Wagoner 6161
V1(mm/s) 51(127) 13(25) 2.5
DP590(B)-CR-1.4 5 3 3
DP780(D)-GI-1.4 5 4 4
DP980(D)-GA-1.45 4 4 4
• Maximum Stress Transition, (R/t)*2: V2/V1=0
V1(mm/s) 51(127) 13(25) 2.5
DP590(B)-CR-1.4 4 3 4
DP780(D)-GI-1.4 4 4 5
DP980(D)-GA-1.45 4 4 4
• Maximum Stress Transition, (R/t)*2: V2/V1=0.5
Summary: (R/t)*2 almost independent of material
R. H. Wagoner 6262
Effect of Roller Condition (V2/V1 = 0): DP780(D)
Free rollerFixed roller
(R/t)*1 linefor free roller
(R/t)*1 linefor fixed roller
FreeFixed
* Direction of roller effect agrees with FE simulation (V2/V1=0 only)
R. H. Wagoner 63
400
500
600
700
800
0 0.03 0.06 0.09 0.12
Data 12
Tru
e Str
ess(
MPa)
True Strain
10-1/s 10-2/s10-2 /s 10-3/s
10-3/s 10-4/s
DP590(B)-CR-1.4mm
e=0.1
Jump Tests: DP590(B)-CR-1.4mm
R. H. Wagoner 64
Measurement of Strain Rate Sensitivity
1%1% 4%4%
m
mC
)(1
2
1
2
R. H. Wagoner 65
Preliminary Results: Interrupted Tests
AB C DE F
W. Gan, Unpublished Result, 2008W. Gan, Unpublished Result, 2008
R. H. Wagoner 66
1D Constitutive Equation: DP590(B)-CR-1.4mm
α Hollomon Voce
α1=0.743 K=1065 σo=666.7
α2=0.0035 n=0.182 A=0.5096
B=19.71
m=0.0043
CTTTHTh o2511 00 ),()()H=1.07e-4
CTTTwhere
ffTfo
VoceHollo
25
13
0021
);(
)(),()
sgm
/10,)()2 31
1
2
R. H. Wagoner
Commercial Sheet-Forming FE
• Problems with commercial sheet-forming FE: 1. No thermo-mechanical capability
2. No solid elements
• Solution to Problem 1:1. Calculate the adiabatic constitutive equation2. Use with isothermal FEA
R. H. Wagoner
Hardening Curve under Adiabatic Condition
0p
T dC
( , ) ( , , )adiabatic T
: temperature increase caused by adiabatic deformation heating
0
200
400
600
800
1000
1200
0 0.2 0.4 0.6 0.8 1
Flo
w S
tre
ss (
MP
a)
Plastic Strain
DP590(B)-CR-1.4mmd/dt=0.001/s
Adiabatic=843[1-0.44exp(-7.5)]
25oC=964[1-0.47exp(-3.9)]
R. H. Wagoner
Tensile Test Simulation
0
200
400
600
800
1000
1200
0 0.05 0.1 0.15 0.2
En
gin
eeri
ng
Str
ess
(MP
a)
Engineering Strain
DP780(D)-GI-1.4mm
Identical results:- T-M FE, d/dt=1/s- T-M FE, d/dt=1/s, adiabatic- FE, d/dt=1/s, adiabatic
FE (T=25oC), d/dt=1/s
*T-M = Thermo-Mechanical
R. H. Wagoner
Draw-Bend Simulation
0
0.2
0.4
0.6
0.8
1
1.2
-10 0 10 20 30 40 50 60
No
rmal
ize
d S
tres
s
Front Displacement (mm)
DP780(D)-GI-1.4mmR/t=3.4, V
2/V
1=0
51mm/s(2/s)
Adiabatic lawV
1=51mm/s
(d/dt=2/s)
Isothermal (25oC)51mm/s(2/s)
2.5mm/s
(10-1/s)
0.025mm/s
(10-3/s)
10mm/s
(4X10-1/s)
Typical sheet forming rate:d/dt=10/s