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1 Great Designs in Steel is Sponsored by: ArcelorMittal Dofasco, ArcelorMittal USA, Nucor Corporation, Severstal North w w America, w. a u t o Inc. s t and e e l United. o r g States Steel Corporation

2 Center for Advanced Materials and Manufacturing of Automotive Components Unique Formability of Advanced High Strength Steel R.H. Wagoner, Ji Hyun Sung, Ji Hoon Kim Dept. of Materials Science and Engineering Ohio State University

3 PROJECT OBJECTIVES (Sponsors: A/SP, DOE, NSF, TREP) Produce and characterize shear failures Develop an improved formability criterion Jim Fekete et al, AHSS Workshop, 2006

4 UNEXPECTED FORMABILITY: AHSS Comparison between FE / FLD simulation and practice. Stoughton, AHSS Workshop, 2006

5 DRAW-BEND TESTER Draw-Bend Test Draw Over Die Radius

6 Start D-B FORMABILITY TESTING: V 1, V 2 CONSTANT mm (10 ) mm V 2 = αv 1 Max. Finish R mm Specimen width: 1 (25.4mm) Tool Radii: 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) u f V 1 Sta art mm(10 ) α: 0 and 0.3 Max. Finish [Madeshia et al., 2008]

7 PHENOMENOLOGICAL FAILURE TYPES V2 Type III 65 o Type II 65 o Type I V1 Type I: Tensile failure (unbent region) Type II: Shear failure (not Type I or III) Type III: Shear failure (fracture at the roller)

8 * R =4 t 2 EFFECT OF R/t: V 1 =127mm/s, V 2 /V 1 =0 DP590(C)-GA-1.75mm DP590(B)-CR-1.4mm σ max R * =6 t 1 V 1 = 127 mm/s Type III Type I V /V = R/t

9 EFFECT OF MAX. BEND STRAIN RATE: V 2 /V 1 = R/t = R/t = 6.46 R/t = R/t = 2.57 σ max 0.9 R/t = DP590(C)-GA-1.75mm V 2 /V 1 = dε/dt (/s)

10 FLIR MEASUREMENTS T max ~ 50 to 100 o C near fracture DP590(C)-GA-1.4mm, V 1 =127mm/sec, V 2 /V 1 =0

11 60 FAILURE TYPE MAP: DP780, V 2 /V 1 = V 1 (mm m/sec) TYPE III TYPE II DP780(D)-GI-1.4mm V /V = Fixed roller TYPE I R/t

12 60 SUMMARY: FAILURE TYPE MAP(V 2 /V 1 =0) V (mm m/sec) TYPE III DP590(B) TRIP780(D) DP980(D) DP780(D) TYPE I or TYPE II 10 V 2 /V 1 =0 Fixed roller R/t

13 (R/t)* 1, V 2 /V 1 =0 SUMMARY: (R/t)* 1 varies with material and V 1 V 1 (mm/s): TRIP780(D)-GA DP590(B)-CR DP780(D)-GI DP980(D)-GA-1.45-RD DP980(D)-GA-1.45-TD (R/t)* 1, V 2 /V 1 =0.3 V 1 (mm/s): DP590(B)-CR TRIP780(D)-GA DP780(D)-GI DP980(D)-GA * Lower (R/t)* 1 is better

14 U f AS A MEASURE OF FORMABILITY 40 Front For rce (F f, KN) Yield Force U f Measure of Formability 0 DP980(D)-GA-1.45mm Front Displacement (U f, mm)

15 U f : V 1 =51mm/SEC (α = 0 vs. 0.3) Front Displac cement (U, mm) f V =51mm/sec 1 V /V =0 2 1 DP590 RD TRIP780 DP780 DP980(D) R/t Max. Front Disp placement (U f, mm) 100 DP TRIP DP DP980(D) 20 V 1 =51mm/sec V /V = RD R/t

16 U f : DP980 (RD vs. TD) Max. Front Displa acement (U, mm) f DP980(D)-GA-1.45mm V 1 =51mm/sec V 2 /V 1 =0 Bend Failure (TD only) RD TD R/t

17 U f (mm), V 2 /V 1 =0 SUMMARY: MAX. FRONT DISPLACEMENTS, U f R/t: DP590(B)-CR TRIP780(D)-GA DP780(D)-GI DP980(D)-GA-1.45-RD DP980(D)-GA-1.45-TD U f (mm), V2/V1=0.3 R/t: DP590(B)-CR TRIP780(D)-GA DP780(D)-GI DP980(D)-GA-1.45-RD DP980(D)-GA-1.45-TD * Higher U f is better

18 H/V CONSTITUTIVE EQUATION: FRAMEWORK Special: σ = f ( ε, T ) g( & ε ) h( T ) f ( ε, T ) = α( T ) f + ( 1- α( T )) f, α( T ) = α -α T Hollomon Voce 1 2 where f Kε n : Hollomon =, fvoce = σ ( Ae ) 1 Bε 0 Standard: g( & ε ) & ε = & ε 0 m h( T ) = ( 1- C T )

19 Effective Stress (MPa) H/V CONSTITUTIVE EQUATION: LARGE-STRAIN VERIFICATION DP mm 25 o C dε/dt=10-3 /sec Fit Range Tensile Test Hollomon <σ>=4mpa H/V <σ>=1mpa Bulge Test (r=0.84, m=1.83) Effective Strain Voce <σ>=1mpa Extrapolated, Bulge Test Range

20 TENSILE TEST FEA: THERMO-MECHANICAL (T-M) T initial = 25 o C Grip H metal-air = 20 W/m 2 K Sample Abaqus Standard (V6.7) 3D solid elements (C3D8RT), 2 layers Von Mises, isotropic hardening Symmetric model Gage region (2% taper) H 2 metal-metal = 5 kw/m K Grip

21 PREDICTED e f, H/V vs. H, V: 3 ALLOYS, 3 TEMPERATURES e f, average standard deviations, law vs. expt. Hollomon Voce H/V DP (23%) 0.05 (20%) 0.02 (7%) DP (18%) 0.04 (22%) 0.01 (6%) DP (30%) 0.03 (21%) 0.01 (5%)

22 FEA DRAW-BEND MODEL: THERMO-MECHANICAL (T-M) U 2, V 2 H metal-air = 20W/m 2 K Abaqus Standard (V6.7) µ = D solid elements (C3D8RT), 5 layers Von Mises, isotropic hardening Symmetric model H metal-metal = 5kW/m 2 K U 1, V 1

23 ISOTHERMAL SIMULATION: DP980, V 1 =51mm/sec, V 2 =0, R/t=6.6 (TYPE I)

24 T-M SIMULATION: DP980, V 1 =51mm/sec, V 2 =0, R/t=6.6 (TYPE III)

25 ROLE OF THERMAL EFFECTS Isothermal simulation (Type I) Front Force (kn) Measured Nonisothermal simulation (Type III) Front Displacement (mm) DP590(B)-CR-1.4mm R/t=3.4, V 1 =127mm/s, V 2 /V 1 =0 Solid elements, 5 layers

26 FAILURE TYPE MAP (V 2 /V 1 =0) TYPE III TYPE I V (mm m/sec) Experiment FE Predicted DP980(D)-GA-1.45mm V 2 /V 1 =0 Fixed roller R/t

27 TEMPERATURE AT MAX. F 1 (DP590): SIMULATED VS. MEASURED 87 o C T-M FEA 80 o C IR Meas. 99 o C T-M FEA 93 o C IR Meas. F=F max F=0.9F max F=F max F=0.9F max Type I Type III

28 ROLE OF DRAWING SPEED (V 1 ) u f (mm) Typical Industrial Strain Rate (10/s) DP980(D)-GA-1.45mm V 2 /V 1 =0, R/t= x10-3 1x10-1 1x10 1 1x10 3 1x10 5 V 1 (mm/s) Temperature at Maximum m Force ( o C) dε/dt max (/s)

29 EFFECT OF R/t (V 2 /V 1 =0): T-M FEA VS. EXPERIMENT FE Simulated Measured u f (mm) Type III Type I DP980(D)-GA-1.45mm V 1 = 51 mm/s V 2 /V 1 = R / t

30 80 EFFECT OF R/t (V 2 /V 1 =0.3): T-M FEA VS. EXPERIMENT Measured (mm) FE Simulated Type II Type I u f Type III 20 DP980(D)-GA-1.45mm V 1 = 51 mm/s V 2 /V 1 = R / t

31 U f PREDICTION ERROR: T-M VS. ISOTHERMAL FEA U error f U (FEA)-U (Experiment) f f U (Experiment) f V 2 /V 1 =0 R/t T-M ISO T-M ISO T-M ISO DP780(D) 8% 29% 6% 18% 17% 7% DP980(D) 16% 32% 5% 26% 5% 17%

32 U f AND TYPE PREDICTION: 25mm SPECIMEN vs. PLANE STRAIN w=25mm Type I u f (mm) Type III Plane Strain (2D, 3D) 10 DP980(D)-GA-1.45mm V 1 = 51 mm/s V 2 /V 1 = R / t

33 60 U f SIMULATIONS: ADIABATIC, ISOTHERMAL, T-M Isothermal T-M Type I u f (mm) 30 Adiabatic Type III DP980(D)-GA-1.45mm V 1 = 51 mm/s V 2 /V 1 = R / t dε/dt (/s)

34 CONCLUSIONS Cause of shear failure: deformation heating U f simulation errors: T-M: 8-10%, ISO: 18-25% Damage mechanics not required. (RD!) New D-B formability test developed (V2,V1 constant) Accurate new H/V law, e f error: H,V 20-24%, H/V - 6% Application to practice: PS, adiabatic σ ε U f is sensitive measure of D-B formability

35 Great Designs in Steel is Sponsored by: ArcelorMittal Dofasco, ArcelorMittal USA, Nucor Corporation, Severstal North w w America, w. a u t o Inc. s t and e e l United. o r g States Steel Corporation