draw-bend fracture prediction with dual-phase...
TRANSCRIPT
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Draw-Bend Fracture Prediction with Dual-Phase Steels
R. H. Wagoner
September 25, 2012
AMPT Wollongong, Australia
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R. H. Wagoner
Outline
1. Background – Shear Fracture, 2006 2. DBF Results & Simulations, 2011 Intermediate Conclusions 3. Practical Application, 2012
Ideal DBF Test Recommended Procedure
4. No Ideal Test? Results, Recommended Procedure
2
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1. Background – Shear Fracture, 2006
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Shear Fracture of AHSS – 2005 Case
Jim Fekete et al, AHSS Workshop, 2006
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Shear Fracture of AHSS - 2011
Forming Technology Forum 2012 Web site: http://www.ivp.ethz.ch/ftf12
http://www.ivp.ethz.ch/ftf12
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Unpredicted by FEA / FLD
Stoughton, AHSS Workshop, 2006
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Shear Fracture: Related to Microstructure?
Ref: AISI AHSS Guidelines
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Conventional Wisdom, 2006
Shear fracture… • is unique to AHSS (maybe only DP steels) • occurs without necking (brittle) • is related to coarse, brittle microstructure • is time/rate independent Notes: • All of these based on the A/SP stamping trials, 2005. • All of these are wrong. • Most talks assume that these are true, even today.
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NSF Workshop on AHSS (October 2006) E
long
atio
n (%
)
Tensile Strength (MPa)
0
10
20
30
40
50
60
70
0 600 1200 300 900 1600
MART
Mild BH
Elo
ngat
ion
(%)
600
R. W. Heimbuch: An Overview of the Auto/Steel Partnership and Research Needs [1]
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2. DBF Results & Simulations, 2011
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References: DBF Results & Simulations J. H. Kim, J. H. Sung, K. Piao, R. H. Wagoner: The Shear Fracture of
Dual-Phase Steel, Int. J. Plasticity, 2011, vol. 27, pp. 1658-1676. J. H. Sung, J. H. Kim, R. H. Wagoner: A Plastic Constitutive Equation
Incorporating Strain, Strain-Rate, and Temperature, Int. J. Plasticity, 2010, vol. 26, pp. 1746-1771.
J. H. Sung, J. H. Kim, R. H. Wagoner: The Draw-Bend Fracture Test (DBF)
and Its Application to DP and TRIP Steels, Trans. ASME: J. Eng. Mater. Technol., (in press)
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DBF 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)
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DBF Test: Effect of R/t
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“H/V” Constitutive Eq.: Large-Strain Verification
600
700
800
900
1000
0.1 0.2 0.3 0.4 0.5 0.6 0.7
Effe
ctiv
e St
ress
(MPa
)
Effective Strain
H/V =1MPa
DP590(B), RDStrain Rate=10-3/sec25oC
Tensile TestVoce =1MPa
Hollomon =4MPa
Bulge Test (r=0.84, m=1.83)
FitRange Extrapolated, Bulge Test Range
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0 0.05 0.1 0.15 0.2 0.25 0.3300
400
500
600
700
Engi
neer
ing
Stre
ss (M
Pa)
Engineering Strain
Experiment(D-B)
Voce HollomonH/V model
DP590(B), RDStrain Rate=10-3/s100oC, Isothermal
FE Simulated Tensile Test: H/V vs. H, V
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Predicted ef, H/V vs. H, V: 3 alloys, 3 temperatures
16
Hollomon Voce H/V
DP590 0.05 (23%) 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%)
Standard deviation of ef: simulation vs. experiment
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FE Draw-Bend Model: Thermo-Mechanical (T-M)
hmetal,air = 20W/m2K
hmetal,metal = 5kW/m2K
µ = 0.04
U1, V1
U2, V2
• Abaqus Standard (V6.7) • 3D solid elements (C3D8RT), 5 layers • Von Mises, isotropic hardening • Symmetric model
Kim et al., IDDRG, 2009
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Front Stress vs. Front Displacement
18
0
200
400
600
800
1000
0 20 40 60 80
Fron
t Str
ess,
σ1
Front Displacement, U1 (mm)
Measured
DP780-1.4mm, RDV
1=51mm/s, V
2/V
1=0
R/t=4.5
IsothermalSolid, Shell
T-M
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Displacement to Maximum Front Load vs. R / t
19
0
20
40
60
80
0 2 4 6 8 10 12 14
UM
ax. L
oad
(mm
)
R / t
Type I
Type III
DP780-1.4mm, RDV
1=51mm/s, V
2/V
1=0
T-M, Solid
Measured
Isothermal, Solid
Isothermal, Shell
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Is shear fracture of AHSS brittle or ductile?
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Fracture Strains: DP 780 (Typical)
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Fracture Strains: TWIP 980 (Exceptional)
22
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Directional DBF : DP 780 (Typical)
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Directional DBF Formability: DP980 (Exceptional)
24
0
5
10
15
20
25
30
0 30 60 90
Elon
gatio
n to
Fra
ctur
e (m
m)
Angle to RD (degree)RD TD
DP980R/t = 3.3
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Interim Conclusions
• “Shear fracture” occurs by plastic localization.
• Deformation-induced heating dominates the error in predicting shear failures.
• Brittle cracking can occur. (Poor microstructure or exceptional tensile ductility, e.g. TWIP).
• T-dependent constitutive equation is essential.
• Shear fracture is predictable plastically. (Challenges: solid elements, T-M model.)
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R. H. Wagoner 26
3. Practical Application - 2012
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DBF/FE vs. Industrial Practice/FE
Ind.: Plane strain High rate ~Adiabatic FE: Shell Isothermal Static
DBF: General strain Moderate rates Thermo-mech. FE: Solid element Thermo-mech.
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Ideal DBF Test: Plane Strain, High Rate
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Ideal Test Results - Stress
29
400
600
800
1000
1200
0 2 4 6 8 10 12 14
Peak
Eng
inee
ring
Stre
ss (M
Pa)
Bending Ratio, R / t
DP780-1.4mm
Analytical PS Result
(UTS)
(R/t)*
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Ideal Test Results - Strain
30
0
0.1
0.2
0.3
0.4
0 2 4 6 8 10 12 14 16
True
Str
ain
Bending Ratio, R / t
Analytical PS ResultsDP 780 - 1.4mm
Outer Strains
Inner Strains
Center Strains(Membrane) FLDo
(R/t)*
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How to Use Practically: Bend, Unbend Regions
31
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Practical Application of SF FLD – (1) Direct
32
For each element in contact
Known: R, t ε*membrane
Predicted Fracture: εFEA > ε*membrane
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Practical Application of SF FLD – (2) Indirect
33
For each element drawn over contact
Known: (R, t)contact Pmax σ*PS tension ε*PS tension
Predicted Fracture: εFEA > ε*PS tension
Wu, Zhou, Zhang, Zhou, Du, Shi: SAE 2006-01-0349.
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Calculation: Indirect Method
34
Example: von Mises Yield, Hollomon Hardening
Von Mises: 𝝈∗𝑷𝑷𝑷 =𝟑𝟐𝑷𝒎𝒎𝒎 𝑨
Hollomon: 𝝈 = 𝑲 𝜺 𝒏
So: 𝝈∗𝑷𝑷𝑷 =𝟑𝟐𝑲 𝜺∗𝑷𝑷𝑷
𝒏 𝜺∗𝑷𝑷𝑷 =𝟐𝟑
𝝈∗
𝑲
𝟏/𝒏
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R. H. Wagoner
Recommended Procedure with Industrial FEA
35
1. Use adiabatic law in FEA, use rate sensitivity
2. Classify each element based on X-Y position (tooling) a) Bend (plane-strain) b) After bend (plane-strain) c) General (not Bend, not After)
3. Apply 4 criteria: a) FLD (Bend, After) b) Direct SF (Bend) c) Indirect SF (After) d) Brittle Fracture* (All?)
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4. No Ideal Test? (What to do?)
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What is Needed?
37
Pmax = f(R/t) (PS, high-speed DBF)
400
600
800
1000
1200
0 2 4 6 8 10 12 14
Peak
Loa
d (M
Pa)
Bending Ratio, R / t
0
0.1
0.2
0.3
0.4
0 2 4 6 8 10 12 14 16
Mem
bran
e St
rain
Bending Ratio, R / t
ε∗membrane = f(R/t) (PS, high-speed DBF)
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R. H. Wagoner 38
FE Plane Strain DBF Model
µ = 0.06
U1, V1
U2, V2 = 0
• Abaqus Standard (V6.7) • Plane strain solid elements (CPE4R), 5 layers • Von Mises, isotropic hardening • Isothermal, Adiabatic, Thermo-Mechanical
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0
400
800
1200
1600
0 0.2 0.4 0.6 0.8 1
True
Str
ess
(MPa
)
True Plastic Strain
DP980(D)-GA-1.45mmdε/dt=10-3/s
Adiabatic
25oC75oC
125oC
-5% -12%
Adiabatic Constitutive Equation
0p
T dC
εη σ ερ
∆ = ∫
( , ) ( , , )adiabatic Tσ ε ε σ ε ε= ∆
39
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R. H. Wagoner
Peak Stress, Plane-Strain: DP980
40
600
800
1000
1200
1400
0 2 4 6 8 10 12 14
Peak
Eng
inee
ring
Stre
ss (M
Pa)
R / t
DP980-1.43mm
Analytical Model,Plane StrainPS FE Model,m=0, µ=0
UTS
DBF measured(RD, TD)
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Membrane Strains at Maximum Load
41
0
0.05
0.1
0.15
0.2
0.25
0 2 4 6 8 10 12 14 16
ε s, T
rue
Mem
bran
e St
rain
Bending Ratio, R / t
Analytical Adiabatic ModelStopped at Maximum LoadDP590
DP780
DP980
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R. H. Wagoner
Analytical Model: Model vs. Fit
42
0
0.02
0.04
0.06
0.08
0.1
0 0.1 0.2 0.3 0.4 0.5 0.6
∆ε s
, Tru
e M
embr
ane
Stra
in
1 / Bending Ratio, t / R
Analytical Adiabatic ModelStopped at Maximum Load
DP590S = 0.167, ε
so = 0.138
DP780S = 0.198, ε
so = 0.101
DP980S = 0.221, εs
o = 0.088
−+
ε=
ε
maxmax
oss R
tRtS
Rt
Rt
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R. H. Wagoner
Analytical Model: Model vs. Fit
43
0
0.05
0.1
0.15
0.2
0.25
0 2 4 6 8 10 12 14 16
ε s, T
rue
Mem
bran
e St
rain
Bending Ratio, R / t
Analytical Adiabatic ModelStopped at Maximum Load
DP590: S = 0.168, ε
so = 0.138
DP780: S = 0.198, εs
o = 0.101
DP980: S = 0.221, ε
so = 0.088
−+
ε=
ε
maxmax
oss R
tRtS
Rt
Rt
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R. H. Wagoner 44
Conclusions
• Shear fracture is predictable with careful testing or careful
constitutive modeling and FEA.
• “Shear fracture” occurs by plastic localization.
• “Shear fracture” is an inevitable consequence of draw-bending mechanics. All materials.
• Brittle fracture can occur, but is unusual. (Poor microstructure or
v. high tensile tensile limit, e.g. TWIP).
• T-dependent constitutive equation is essential for AHSS because of high plastic work. (But probably not Al or many other alloys.)
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R. H. Wagoner 45
Thank you.
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R. H. Wagoner 46
References
• R. H. Wagoner, J. H. Kim, J. H. Sung: Formability of Advanced High Strength Steels, Proc. Esaform 2009, U. Twente, Netherlands, 2009 (CD)
• J. H. Sung, J. H. Kim, R. H. Wagoner: A Plastic Constitutive Equation Incorporating Strain, Strain-Rate, and Temperature, Int. J. Plasticity, (accepted).
• A.W. Hudgins, D.K. Matlock, J.G. Speer, and C.J. Van Tyne, "Predicting Instability at Die Radii in Advanced High Strength Steels," Journal of Materials Processing Technology, vol. 210, 2010, pp. 741-750.
• J. H. Kim, J. Sung, R. H. Wagoner: Thermo-Mechanical Modeling of Draw-Bend Formability Tests, Proc. IDDRG: Mat. Prop. Data for More Effective Num. Anal., eds. B. S. Levy, D. K. Matlock, C. J. Van Tyne, Colo. School Mines, 2009, pp. 503-512. (ISDN 978-0-615-29641-8)
• R. H. Wagoner and M. Li: Simulation of Springback: Through-Thickness Integration, Int. J. Plasticity, 2007, Vol. 23, Issue 3, pp. 345-360.
• M. R. Tharrett, T. B. Stoughton: Stretch-bend forming limits of 1008 AK steel, SAE technical paper No.2003-01-1157, 2003.
• M. Yoshida, F. Yoshida, H. Konishi, K. Fukumoto: Fracture Limits of Sheet Metals Under Stretch Bending, Int. J. Mech. Sci., 2005, 47, pp. 1885-1896.
http://www.sciencedirect.com/science?_ob=IssueURL&_tockey=
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R. H. Wagoner 47
Extra Slides
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DP Steels
48
0
200
400
600
800
1000
1200
0 5 10 15 20 25
Engi
neer
ing
Stre
ss(M
Pa)
Engineering Strain (%)
DP590(B)-1.4mm
DP780(D)-1.4mm
DP980(D)-1.45mm
Strain Rate: 10-3/secRoom Temp.Rolling Direction
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R. H. Wagoner 49
“H/V” Constitutive Framework
Special:
Standard:
( , , ) ( , ) ( ) ( )T f T g h Tσ σ ε ε ε ε= = ⋅ ⋅
( , ) ( ) (1 ( ))Hollo Vocef T T f T fε α α= + − ⋅
1 2( ) ( )RTT T Tα α α= − −n
Hollof Kε= [1 exp( )]Vocef A B Cε= − −
[log ]
0
( )a b
gε
εε
ε
+
=
( ) (1 ( ))RTh T D T T= − ⋅ − Sung et al., Int. J. Plast. 2010
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Simulated D-B Test: Effect of Draw Speed
50
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25 30 35
F/F U
TS
Front Displacement (mm)
DP980(D)R/t=4.4, V
2/V
1=0
51mm/s(dε/dt=2.5/s)
Adiabatic
Isothermal
2.5mm/s(0.13/s)
0.001mm/s(5x10-3/s)
13mm/s(0.6/s)
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DBF Formability: DP980(A), RD vs. TD (Typical)
51
* Directional Formability: TD=RD
0
10
20
30
40
50
2.2 3.4 4.5 5.5 6.6 7.8 10 13.3
Fron
t Dis
p. to
Fai
lure
(Uf,
mm
)
R/t
RDTD
DP980(A)V
1=51mm/sec
V2/V
1=0
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R. H. Wagoner
DBF Formability: DP980(D), RD vs. TD (Exceptional)
52
* Directional Formability: RD>TD
0
10
20
30
40
50
60
2.2 3.3 4.4 5.4 6.6 7.7 9.9 13.1
Fron
t Dis
p. to
Fai
lure
(Uf,
mm
)
R/t
DP980(D)V
1=51mm/sec
V2/V
1=0
RD
TD
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Analytical Model – Curvilinear Derivation
Rrn
Neutral liner
θ t
T T
lnn
r
rθε =
2 2ln
3 3ij ij
n
r
rε ε ε= =
53
Fracture Criterion: Fracture occurs at Tmax for given R, to
2 2 2( ) ( )3 3 3
n
n
rR t
r r
r dr dr rθθσ σ σ σ+
= − −
∫ ∫
0R tR t
R R
Trdr dθθ θθσ σ ξξ
++
=∂
=∂∫ ∫
2 2( ) ( )3 3
R t
r
r dr rθθσ σ σ+
= +
∫
Materially embedded coordinate :ξ
nr
rdr d dr
λ ξ ξ= =
0 2 2( ) ( )3 3
R t r dθθξ
σ ξ σ ξ σ ξξ
+ ∂ = + ∂
∫
0 2 2 2( ) ( )3 3 3
n
n
R t r rd dξ
θθξ ξ
σ ξ σ ξ σ ξ σ ξξ ξ
+ ∂ ∂ = − − ∂ ∂
∫ ∫
nr r>
nr r<
nξ ξ>
nξ ξ
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R. H. Wagoner
DBF Interpretation: Plane-strain vs. Tension
400
600
800
1000
1200
0 2 4 6 8 10 12 14
Peak
Eng
inee
ring
Stre
ss (M
Pa)
R / t
DP780-1.4mm
Analytical Model,Plane Strain
Simplified FE Model,m=0, µ=0
UTS
54
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Inner and Outer Strains at Maximum Load
55
0
0.1
0.2
0.3
0.4
0 2 4 6 8 10 12 14 16
True
Str
ain
Bending Ratio, R / t
Analytical Adiabatic ModelStopped at Maximum Load
DP590
DP780
Inner Strains
DP980
Outer Strains
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Membrane Strains (R/t Affected Only)
56
0
0.05
0.1
0.15
0.2
0.25
0 2 4 6 8 10 12 14 16
∆ε s
, Tru
e M
embr
ane
Stra
in
Bending Ratio, R / t
Analytical Adiabatic ModelStopped at Maximum Load
DP590
DP780DP980
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R/t-Affected Membrane Strains vs. t/R
57
0
0.05
0.1
0.15
0.2
0.25
0 0.1 0.2 0.3 0.4 0.5 0.6
∆ε s
, Tru
e M
embr
ane
Stra
in
1 / Bending Ratio, t / R
Analytical Adiabatic ModelStopped at Maximum Load
DP590
DP780
DP980
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Forming Limit Diagram
58
Ref: Hosford & Duncan
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PS T-M Model: Model vs. Fit
59
-0.05
0
0.05
0.1
0.15
0.2
0.25
0 0.1 0.2 0.3 0.4
∆ε s
, Tru
e M
embr
ane
Stra
in
1 / Bending Ratio, t / R
Plane Strain Thermo-Mechanical ModelStopped at Maximum Load DP590
S = 0.753, εs
o = 0.149
DP780S = 0.330, ε
so = 0.123
DP980S = 0.051, ε
so = 0.133
−+
ε=
ε
maxmax
oss R
tRtS
Rt
Rt
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PS T-M Model: Model vs. Fit
60
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10 12 14 16
ε s, T
rue
Mem
bran
e St
rain
Bending Ratio, R / t
Plane Strain Thermo-Mechanical ModelStopped at Maximum Load
DP590S = 0.753, ε
so = 0.149
DP780: S = 0.330, εs
o = 0.123
DP980: S = 0.051, εs
o = 0.133
−+
ε=
ε
maxmax
oss R
tRtS
Rt
Rt
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R. H. Wagoner 61
Draw-Bend Fracture Test (DBF): V1, V2 Constant
Star
t
Max. Finish
Max
. Fin
ish
V1
Start
R
444.5 mm (10”) 190.5 mm
190.
5 m
m
444.
5 m
m(1
0”)
V2 = αV1
uf
Specimen width: 25mm Tool radius choices: 2/16, 3/16, 4/16, 5/16, 6/16, 7/16, 9/16, 12/16 inch 3.2, 4.8, 6.4, 7.9, 9.5, 11.1, 14.3, 19 mm α = V2/V1: 0 and 0.3
Wagoner et al., Esaform, 2009
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AHSS vs. HSLA
62
Ref: AISI AHSS Guidelines
Draw-Bend Fracture Prediction with Dual-Phase SteelsOutlineSlide Number 3Shear Fracture of AHSS – 2005 CaseShear Fracture of AHSS - 2011Unpredicted by FEA / FLDShear Fracture: Related to Microstructure?Conventional Wisdom, 2006NSF Workshop on AHSS (October 2006)Slide Number 10References: DBF Results & SimulationsDBF Failure Types DBF Test: Effect of R/tSlide Number 14Slide Number 15Predicted ef, H/V vs. H, V: 3 alloys, 3 temperaturesFE Draw-Bend Model: Thermo-Mechanical (T-M)Front Stress vs. Front DisplacementDisplacement to Maximum Front Load vs. R / tSlide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Interim ConclusionsSlide Number 26DBF/FE vs. Industrial Practice/FEIdeal DBF Test: Plane Strain, High RateIdeal Test Results - StressIdeal Test Results - StrainHow to Use Practically: Bend, Unbend RegionsPractical Application of SF FLD – (1) DirectPractical Application of SF FLD – (2) IndirectCalculation: Indirect MethodRecommended Procedure with Industrial FEASlide Number 36What is Needed?FE Plane Strain DBF ModelAdiabatic Constitutive EquationPeak Stress, Plane-Strain: DP980Membrane Strains at Maximum LoadAnalytical Model: Model vs. FitAnalytical Model: Model vs. FitConclusionsSlide Number 45ReferencesSlide Number 47DP SteelsSlide Number 49Simulated D-B Test: Effect of Draw SpeedSlide Number 51Slide Number 52Analytical Model – Curvilinear DerivationDBF Interpretation: Plane-strain vs. TensionInner and Outer Strains at Maximum LoadMembrane Strains (R/t Affected Only)R/t-Affected Membrane Strains vs. t/RForming Limit DiagramPS T-M Model: Model vs. FitPS T-M Model: Model vs. FitDraw-Bend Fracture Test (DBF): V1, V2 ConstantAHSS vs. HSLA