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Draw-Bend Fracture Prediction with Dual-Phase Steels

Draw-Bend Fracture Prediction with Dual-Phase Steels. R. H. Wagoner September 25, 2012 AMPT Wollongong, Australia. Outline. Background – Shear Fracture, 2006 DBF Results & Simulations, 2011 Intermediate Conclusions Practical Application, 2012 Ideal DBF Test Recommended Procedure

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Draw-Bend Fracture Prediction with Dual-Phase Steels

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  1. Draw-Bend Fracture Prediction with Dual-Phase Steels R. H. Wagoner September 25, 2012 AMPT Wollongong, Australia

  2. 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 2

  3. Background – Shear Fracture, 2006 3

  4. Shear Fracture of AHSS – 2005 Case Jim Fekete et al, AHSS Workshop, 2006

  5. Shear Fracture of AHSS - 2011 Forming Technology Forum 2012 Web site: http://www.ivp.ethz.ch/ftf12

  6. Unpredicted by FEA / FLD Stoughton, AHSS Workshop, 2006 6

  7. Shear Fracture: Related to Microstructure? Ref: AISI AHSS Guidelines

  8. 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.

  9. NSF Workshop on AHSS (October 2006) 70 L-IP 60 AUST. SS TWIP 50 IF IF- HS 40 Elongation (%) Elongation (%) Mild ISO ISO 30 BH TRIP CMn 20 HSLA DP, CP 10 MART 0 0 300 600 600 900 1200 1600 Tensile Strength (MPa) R. W. Heimbuch: An Overview of the Auto/Steel Partnership and Research Needs [1] 9 9 9

  10. 2. DBF Results & Simulations, 2011 10

  11. 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) 11

  12. DBF Failure Types V2 Type III Type II 65o Type I 65o V1 Type I: Tensile failure (unbent region) Type II: Shear failure (not Type I or III) Type III: Shear failure (fracture at the roller) 12

  13. DBF Test: Effect of R/t 13

  14. “H/V” Constitutive Eq.: Large-Strain Verification 14

  15. FE Simulated Tensile Test: H/V vs. H, V 15

  16. Predicted ef, H/V vs. H, V: 3 alloys, 3 temperatures Standard deviation of ef: simulation vs. experiment 16

  17. FE Draw-Bend Model: Thermo-Mechanical (T-M) • Abaqus Standard (V6.7) • 3D solid elements (C3D8RT), 5 layers • Von Mises, isotropic hardening • Symmetric model U2, V2 hmetal,air = 20W/m2K m = 0.04 hmetal,metal = 5kW/m2K Kim et al., IDDRG, 2009 U1, V1

  18. Front Stress vs. Front Displacement 18

  19. Displacement to Maximum Front Load vs. R / t 19

  20. Is shear fracture of AHSS brittle or ductile? 20

  21. Fracture Strains: DP 780 (Typical) 21

  22. Fracture Strains: TWIP 980 (Exceptional) 22

  23. Directional DBF : DP 780 (Typical) 23

  24. Directional DBF Formability: DP980 (Exceptional) 24

  25. 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.) 25

  26. 3. Practical Application - 2012 26

  27. 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. 27

  28. Ideal DBF Test: Plane Strain, High Rate 28

  29. Ideal Test Results - Stress 29

  30. Ideal Test Results - Strain 30

  31. How to Use Practically: Bend, Unbend Regions 31

  32. Practical Application of SF FLD – (1) Direct For each element in contact Known: R, t e*membrane Predicted Fracture: eFEA > e*membrane 32

  33. Practical Application of SF FLD – (2) Indirect For each element drawn over contact Known: (R, t)contactPmax s*PS tension  e*PS tension Predicted Fracture: eFEA> e*PS tension Wu, Zhou, Zhang, Zhou, Du, Shi: SAE 2006-01-0349. 33

  34. Calculation: Indirect Method 34

  35. 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?) 35

  36. 4. No Ideal Test? (What to do?) 36

  37. What is Needed? e*membrane = f(R/t) (PS, high-speed DBF) Pmax= f(R/t) (PS, high-speed DBF) 37

  38. FE Plane Strain DBF Model • Abaqus Standard (V6.7) • Plane strain solid elements (CPE4R), 5 layers • Von Mises, isotropic hardening • Isothermal, Adiabatic, Thermo-Mechanical m = 0.06 U2, V2 = 0 U1, V1

  39. Adiabatic Constitutive Equation 39

  40. Peak Stress, Plane-Strain: DP980 40

  41. Membrane Strains at Maximum Load 41

  42. Analytical Model: Model vs. Fit 42

  43. Analytical Model: Model vs. Fit 43

  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.) 44

  45. Thank you. 45

  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. 46

  47. Extra Slides 47

  48. DP Steels 48

  49. “H/V” Constitutive Framework Special: Standard: Sung et al., Int. J. Plast. 2010

  50. Simulated D-B Test: Effect of Draw Speed 50

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