Draw-Bend%20Fracture%20Prediction%20with%20Dual-Phase%20Steels

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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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Outline

• Background Shear Fracture, 2006
• DBF Results Simulations, 2011
• Intermediate Conclusions
• Practical Application, 2012
• Ideal DBF Test
• Recommended Procedure
• No Ideal Test?
• Results,
• Recommended Procedure

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• 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
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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)
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L-IP
60
AUST. SS
TWIP
50
IF
IF- HS
Elongation ()
40
Elongation ()
Mild
ISO
ISO
30
BH
TRIP
CMn
20
HSLA
DP, CP
10
MART
0
0
600
1200
300
900
1600
600
Tensile Strength (MPa)
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 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
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FE Simulated Tensile Test H/V vs. H, V
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Predicted ef, H/V vs. H, V 3 alloys, 3
temperatures
Standard deviation of ef simulation vs.
experiment
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)
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FE Draw-Bend Model Thermo-Mechanical (T-M)
U2, V2
hmetal,air 20W/m2K

• Abaqus Standard (V6.7)
• 3D solid elements (C3D8RT), 5 layers
• Von Mises, isotropic hardening
• Symmetric model

m 0.04
hmetal,metal 5kW/m2K
Kim et al., IDDRG, 2009
U1, V1
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Front Stress vs. Front Displacement
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Displacement to Maximum Front Load vs. R / t
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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)
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Directional DBF DP 780 (Typical)
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Directional DBF Formability DP980 (Exceptional)
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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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• 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
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Ideal Test Results - Strain
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How to Use Practically Bend, Unbend Regions
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Practical Application of SF FLD (1) Direct
For each element in contact Known R, t ?
emembrane Predicted Fracture eFEA gt
emembrane
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Practical Application of SF FLD (2) Indirect
For each element drawn over contact Known (R,
t)contact ? Pmax ? sPS tension ? ePS tension
Predicted Fracture eFEA gt ePS tension
Wu, Zhou, Zhang, Zhou, Du, Shi SAE 2006-01-0349.
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Calculation Indirect Method
 
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Recommended Procedure with Industrial FEA

• Use adiabatic law in FEA, use rate sensitivity
• Classify each element based on X-Y position
  (tooling)
• Bend (plane-strain)
• After bend (plane-strain)
• General (not Bend, not After)
• Apply 4 criteria
• FLD (Bend, After)
• Direct SF (Bend)
• Indirect SF (After)
• Brittle Fracture (All?)

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• 4. No Ideal Test?
• (What to do?)

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What is Needed?
emembrane f(R/t) (PS, high-speed DBF)
Pmax f(R/t) (PS, high-speed DBF)
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FE Plane Strain DBF Model
m 0.06
U2, V2 0

• Abaqus Standard (V6.7)
• Plane strain solid elements (CPE4R), 5 layers
• Von Mises, isotropic hardening
• Isothermal, Adiabatic, Thermo-Mechanical

U1, V1
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Adiabatic Constitutive Equation
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Peak Stress, Plane-Strain DP980
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Membrane Strains at Maximum Load
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Analytical Model Model vs. Fit
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Analytical Model Model vs. Fit
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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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• Thank you.

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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.

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• Extra Slides

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DP Steels
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H/V Constitutive Framework
Special
Standard
Sung et al., Int. J. Plast. 2010
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Simulated D-B Test Effect of Draw Speed
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DBF Formability DP980(A), RD vs. TD (Typical)
Directional Formability TDRD
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DBF Formability DP980(D), RD vs. TD
(Exceptional)
Directional Formability RDgtTD
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Analytical Model Curvilinear Derivation
Fracture Criterion Fracture occurs at Tmax for
given R, to
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DBF Interpretation Plane-strain vs. Tension
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Inner and Outer Strains at Maximum Load
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Membrane Strains (R/t Affected Only)
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R/t-Affected Membrane Strains vs. t/R
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Forming Limit Diagram
Ref Hosford Duncan
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PS T-M Model Model vs. Fit
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PS T-M Model Model vs. Fit
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Draw-Bend Fracture Test (DBF) V1, V2 Constant
190.5 mm
Start
444.5 mm (10)
V2 aV1
Max. Finish
R
190.5 mm
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 a V2/V1 0 and 0.3
444.5 mm(10)
Start
uf
V1
Max. Finish
Wagoner et al., Esaform, 2009
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AHSS vs. HSLA
Ref AISI AHSS Guidelines
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