collaborative project between Steel Marketing Development .../media/Files/Autosteel/Great Designs in Steel... · Taamjeed Rahmaan Kaab Omer. 3 #GDIS | #SteelMatters Overview Background

GDIS2017

Fracture Characterization of Advanced 980 MPa Steels

- collaborative project between Steel Marketing Development Institute, Honda

Research America, and University of Waterloo

Cliff Butcher Jim Dykeman

University of Waterloo Honda R&D America

#GDIS | #SteelMatters 2

Project Team Steel Marketing Development: Hesham Ezzat, Dave Anderson ArcelorMittal: Steve Lynes, Tim Lim AK Steel: Kavesary Raghavan Nucor: Dean Kanelos, Andy Thompson Honda Research of Americas: Jim Dykeman, Skye Malcolm University of Waterloo: PI’s: Mike Worswick, Cliff Butcher Research Team : Jose Imbert-Boyd Armin Abedini Kenneth Cheong Sante DiCecco Sam Kim Amir Zhumagulov Taamjeed Rahmaan Kaab Omer


Overview

Background

Objective

Study Materials

Fracture Test Methodology and Results

Component Testing

Conclusions


Background

Recent evolution of Advanced High Strength Steel

Common AHSS grades and their application areas


Background

Need for Grade Diversification at 980 Strength Level

Specialized grades now exist at

the 590 and 780 MPa strength

level. (dual phase, TRIP, etc).

Expand Grades at 980 MPa for

enhanced:

- bending

- flanging

- energy absorption

Expand Options at 980 MPa


Background

Microstructures of early DP980 not optimized for bending and edge stretch

These property limitations restricted the application of DP980.

Complex part shapes and features could not be formed.

Energy absorption targets could not be meet due to fracture problems.

CONV 980YL - Increasing Strain -

Fracture of martensite Void Growth Initial

Microstructure*

*Damage in dual phase steel DP1000 (Alharbi, K)


Objectives

1. Characterize properties of various Dual Phase 980 grades selected by

Steel Marketing Development Institute (Blind Study)

2. Investigate optimized fracture testing methodology for Advanced High

Strength Steel Industrial Friendly and Efficient Methods Required

3. Perform experimental axial and bend crush experiments and assess

fracture performance


Project Structure 1. Each Supplier Submits One DP980 to SMDI Sample Bank

2. Material identification removed:

Sent to UW and Honda for Fracture Characterization from Coupons to Crash


Study Materials: Composition 980 #1

SMDI Grades Thickness (mm) Type General Composition Coating

980 Mat#1 1.2 Dual Phase C-Mn-Si Bare

980 Mat#1 1.6 Dual Phase C-Mn-Cr-Mo-Nb Zinc

980 Mat#3 1.4 Dual Phase C-Mn-Si Zinc

980 #2 980 #3

Grades represent recent optimization in processing / chemistry (but are not Gen 3 level)

Materials can generally be described as DP with fine, uniform microstructure.


Study Materials: Tensile Properties

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

En

gin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

SMDI MAT#1

SMDI MAT#2

SMDI MAT#3

Grade TS

(MPa)

YS

(MPa)

YS/TS

Ratio

TE

(%)

#1 L 1046 806 0.81 12.7

T 1067 787 0.74 13.5

#2 L 971 912 0.94 12.9

T 998 934 0.94 12.0

#3 L 989 776 0.78 13.8

T 1012 757 0.75 13.0

Tensile Properties - JIS Test Specimen

All grades exhibited total elongation typical of 980 level material.

Relatively high YS/TS ratios suggested all grades favor local formability.

Material #2 had unique yield point elongation behavior.


0

10

20

30

40

50

60

70

80

90

100

110

120

DP980 -

Material 1

DP980 -

Material 2

DP980 -

Material 3

JAC 980Y

Ben

d A

ng

le ( )

-V

DA

Met

ho

d

Local Ductility Properties - Hole Expansion and Bendability

Grade Hole Expansion (punched) (%)

Bend (VDA Angle)

#1 L

36 105°

T 95°

#2 L

44 102°

T 90°

#3 L

39 110°

T 95°

Performance of these grades is consistent with or above current commercial products.

VDA bend data is of growing industrial importance as means to evaluate material.

The potential use of the VDA test for fracture prediction will be elaborated on in next section

SMDI DP980’s


Characterization for Formability & Fracture

1) Material characterization at large strains and strain rates

2) Efficient method to determine forming limit strains (FLD) (Global formability)

3) Characterization in tight radius bending (Local formability/fracture)

4) Establish best practices and tests for experimental fracture characterization

*Extensive numerical characterization study pursued in tandem

Priority Focus Areas


1. Material Characterization at Large Strains

• Limited hardening data

available in tensile tests

• Inverse FE modeling used to

identify hardening at large

strains for fracture

• Hardening data becomes a

function of numerical model

assumptions... 0

200

400

600

800

1000

1200

1400

1600

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Eq

uiv

ale

nt

Str

ess

(M

Pa)

Equivalent Plastic Strain

Experiment: Tension

DP980 - Material 1Transverse Direction

What is stress

level at fracture?


0

200

400

600

800

1000

1200

1400

1600

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Eq

uiv

ale

nt

Str

ess

(M

Pa

)Equivalent Plastic Strain

Experiment: Converted Shear

Experiment: Tension

Holloman Model

DP980 - Material 1Transverse Direction

0.074

(MPa) 1392 p

1. Material Characterization at Large Strains

• UW developed simple method to

use tensile & shear test data to

obtain hardening to large strain

levels

• DP980 data to 60% strain!

• Not related to FE model

Methodology in Rahmaan, T., et al.,

Int. J. Impact. Eng., 2017 (in-press)


800

900

1000

1100

1200

1300

1400

0 0.02 0.04 0.06 0.08 0.1E

qu

ivale

nt

Str

ess

(M

Pa)

Eq. Plastic Strain

Exp. 0.001 s-1 Exp. 10 s-1 Exp. 100 s-1

Exp. 1000 s-1 Model: 0.001 s-1 Model: 0.10 s-1

Model: 1 s-1 Model: 10 s-1 Model: 100 s-1

Model: 1000 s-1

1000 s-1

0.001 s-1

DP980 - Material 1: Transverse Direction

1. Material Characterization at Large Strains and Strain Rates

• Tensile characterization from

0.001 to 1000 s-1

• Scale quasi-static data obtained

to large strains for strain rates

• Efficient experimental method for

constitutive characterization

,p p QS pF


1. Material Characterization at Large Strains and Strain Rates

0

200

400

600

800

1000

1200

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

En

gin

eerin

g S

tress

(M

Pa

)

Engineering Strain

Experiment Average

Mesh Size: 0.1 mm

DP980 - Material 1: TD JIS Tensile Test

0

200

400

600

800

1000

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Sh

ea

r S

tress

(M

Pa

)

von Mises Eq. Strain

Experiment Average

Mesh Size: 0.1 mm

DP980 - Material 1: 45 Shear Test

FE Simulations using Experimental Hardening Model and Von Mises Perform Well: Efficient


2. Global Formability – FLD Methodology

Physically-motivated FLD detection methods are needed

ISO 12004-2 Standard Method

Curve fitting of strain distributions

(arbitrary, little physical foundation)

UW Curvature Method: “Digital Finger Test” –

Detects surface discontinuity

(DiCecco et al., Exp. Mechanics. Submitted)


2. Forming Limits

Curvature provides physical upper limit

0.00

0.10

0.20

0.30

0.40

0.50

-0.20 -0.10 0.00 0.10 0.20 0.30 0.40 0.50

Majo

r T

ru

e S

train

Minor True Strain

Material: Mat 1 (TD)Thickness: 1.2 mm

Punch Speed: 0.25 mm/s

UW

Curvature

Method

Standard Method

ISO12004:2-2008

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

-0.20 -0.10 0.00 0.10 0.20 0.30 0.40 0.50

Majo

r T

ru

e S

train

Minor True Strain

FLD Method: UW Curvature

Mat #1: t = 1.2 mm

Mat #2: t = 1.6 mm

Mat #3: t = 1.4 mm

Comparable FLDs for Three Grades

Plane Strain Forming Limit ~ 11-14%


Formability in tight-radius bending indentified as key factor in crash performance

VDA 238-100 bend test promising but only reports bend angle

3. Formability and Fracture in Tight Radius Bending

UW-HRA Tailored Hot Stamped Rail (Omer et al., 2017, Int. J. Impact. Eng)

Cracking in tight radius bend

DP980 Material 2

Global Buckling and Folding


Optical VDA238-100 Test Frame

UW & HRA Developed an Inverted Bend Test for Optimal DIC Strain Measurement (IDDRG Conf., 2017)

Initial Position Full Stroke

Sufficient space for DIC access

UW’s VDA238 configuration with DIC

Punch is stationary

Rollers move down

Measure Fracture Strain & Bend Angle!


V-Bending with DIC

Measures width of specimen ( res. < 0.02 mm/pixel)

Homogeneous Strain Distribution along Width

0

1000

2000

3000

4000

5000

6000

7000

8000

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80Lo

ad (

N)

Major True Strain

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

Sample 6

VDA

Load Drop 1

DP980: Material 2 - TD

Load vs Major Strain (Ex: 980 Mat#2)

Detect fracture using Load drop (VDA) or visual cracking


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06

Ma

jor

Tru

e S

tra

in

Minor True Strain

Sample 1

Sample 2

Sample 3

Sample 4

Sample 5

Sample 6

VDA

Load Drop - 1%

DP980: Material 2 - TD

V-Bending with DIC Strain Measurement

Achieves Ideal Plane Strain Loading

until Onset of Cracking

Initial Position Full Stroke

Sufficient space for DIC access

DP980 Plane strain fracture limits of 45-50%!

Forming limit strains ~ 12%

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Material 1:

t = 1.2 mm

Material 2:

t = 1.6 mm

Material 3:

t = 1.4 mmM

ajo

r T

rue

Str

ain

Bending Limit Strain

Forming Limit Strain


Comparison of V-Bend with Plane Strain Notch

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06

Ma

jor

Tru

e S

trai

n

Minor True Strain

Traditional Plane Strain

Notch Tensile Sample

V-Bend with DIC

Disagreement between tests: Notch test is lower…



0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06

Ma

jor

Tru

e S

trai

n

Minor True Strain

Traditional Plane Strain

Notch Tensile Sample

V-Bend with DIC

But a thickness correction on the notch resolves the difference

Conventional DIC

techniques struggle to

capture final thinning

during necking-based

failure .

Thickness measurement of Cross-Section



0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Material 1:

t = 1.2 mm

Material 2:

t = 1.6 mm

Material 3:

t = 1.4 mm

Ma

jor

Tru

e S

tra

in

V-Bend

Plane Strain Notch: DIC + Thinning

Plane Strain Notch: DIC

Plane Strain notch provides lower bound estimate if thinning correction performed

Correction also required for plane strain dome tests

Optical V-Bend Test is Superior

1. No necking

2. Minimal to No Machining

3. Ideal plane strain loading

4. Efficient – low time per test


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Hole Expansion JIS Tensile:

DIC

JIS Tensile:

DIC + Thinning

Method

JIS Tensile:

Area Measurement

Ma

jor

Tru

e S

tra

in

Material 1: DP980-TD

Conical Hole Expansion Test for Fracture in Uniaxial Tension

*Punch appears off-center due to the

alignment of camera.

Through-

Thickness Crack

JIS Hole Expansion Test

Do not use a flat punch

Outer diameter is in uniaxial tension and does not contact the punch Triaxiality = 1/3 (Butcher et al., SAE, 2013, Pathak et al., JMEP, 2016; Numisheet 2016)

(%) 100f

inner o

o

d dHER

d

ln

ff f outer

eq c

o

d

d

Try it !

You’ll like it


4. Fracture Characterization: 10 Test Geometries

3 Nakazima Dome Tests:

Uniaxial, Plane Strain & Biaxial

** Plane Strain **

** (V bend) **

Shear

(Mini Shear)

Intermediary Strain (3 Notch Tensiles)

Uniaxial Tension

(Hole Expansion, JIS Tensile)

FLD


4. Fracture Characterization Results

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-0.7 -0.5 -0.3 -0.1 0.1 0.3 0.5

Ma

jor

Str

ain

Minor Strain

JIS

Mini-shear Smooth

Notch

Tight

Notch

Uniaxial

Dome

Plane Strain

Dome

Biaxial Dome

Plane Strain

Notch

V-bend (Plane strain) ( 0, 0.45 )

Hole Expansion (Uniaxial tension)

( -0.44, 0.87)

• Conflicting limits provided by different specimen types if thinning correction not applied

Min. of 4 Tests can describe

the fracture locus

Four Relatively Simple Tests:

1. Mini-shear

2. Hole expansion (reamed)

3. V-Bend

4. Biaxial/Bulge


4. Experimental Fracture Locus

Four tests can be used to generate physically-meaningful fracture loci

Not the product of a simulation exercise – Real material performance can be assessed

• Relatively comparable fracture loci

• Mat 2 had the lowest hardening rate,

highest hole expansion and v-bend

0.00

0.20

0.40

0.60

0.80

1.00

1.20

-0.10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

Eq

. P

last

ic S

train

Stress Triaxiality

Experimental Fracture Loci: UW ModelDP980 - Transverse Direction

Material 2

Material 1

Material 3


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-0.10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

Eq

. P

last

ic S

tra

in

Stress Triaxiality

Experimental Fracture Loci: DP980 - Material 1: TD

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-0.10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

Eq

. P

last

ic S

tra

in

Stress Triaxiality

Experimental Fracture Loci: DP980 - Material 1: TD

4. Experimental Fracture Locus with Edge Effects

Sheared Edge Failure is a Uniaxial Tensile Mode:

Use Punched Hole Expansion Tests to Obtain Uniaxial Failure Strain with Sheared Edge

0

20

40

60

80

100

120

140

160

180

Material 1 Material 2 Material 3

Hole

Exp

an

sion

Rati

o (%

)

Machined Edge

Sheared Edge: 12% Clearance

DP980

Ideal Edge Condition

Sheared Edge Condition

Strong Edge Sensitivity Across Range of Tensile-Loadings

Sheared

Hole

Expansion


Dynamic Structural Component Evaluation

3-Point Bend Dynamic Crash Test at UW

• Sled Mass: 855kg • Sled Velocity: 25.5km/h • Total Energy: 21kJ • Free Crush Distance: 100mm • Total Crush Distance: 160mm

Axial Crush Dynamic Crash Test at UW

• Sled Mass: 855kg • Sled Velocity: 25.5km/h • Total Energy: 21kJ • Free Crush Distance: 115 mm • Total Crush Distance: 135mm


Dynamic 3-Point Bend Test at UW


Dynamic 3-Point Bend Test Results

980 #1 980 #2

980 #3

Minimal Cracking for the 3 Grades


Dynamic 3-Point Bend Test Results: Mat. 2

Minor cracking not detected in load response 980 #2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0

5

10

15

20

25

30

35

0 0.02 0.04 0.06 0.08 0.1

Ene

rgy

Ab

sorb

ed

[kJ]

Forc

e [k

N]

Displacement [m]

DP980 - Material 2

T1

T2

T3

Average


Dynamic Axial Crush Test: Material 1

Material #1: t = 1.2 mm



Material #3: t = 1.4 mm



0

2

4

6

8

10

12

14

16

18

20

0

20

40

60

80

100

120

140

160

180

0 0.05 0.1 0.15 0.2

Ene

rgy

Ab

sorb

ed

[kJ]

Forc

e [k

N]

Displacement [m]

Mat 3: Dynamic Axial Crush

T1T2T3T4Average

First

Fold

Second

Fold

Lateral

fold


Dynamic Axial Crush Test Results

Material #1: t = 1.2 mm Material #2: t = 1.6 mm Material #3: t = 1.4 mm

Relatively Good

Performance for 3 Grades

Repeatable Energy

Absorption

Material 3 had highest

spot weld strength and

strain rate sensitivity


Conclusions

Efficient and Accurate Experimental Methodologies Established for Characterization

of AHSS

1. Method to experimentally obtain hardening to large strains and strain rates

2. New FLD detection algorithm: Curvature-based

3. Optical V-Bend developed: Ideal plane strain test

4. Four tests required to efficiently obtain fracture locus for a material

As with FLD’s, Use 4 Industrially Friendly Tests to Construct Fracture Locus to

Compare Material Performance Accounts for Edge Condition

New model to use four tests for rapid FE model implementation Next GDIS


For More Information

Jim Dykeman

Honda Research America

[email protected]

Cliff Butcher

University of Waterloo

[email protected]

Documents

collaborative project between Steel Marketing Development .../media/Files/Autosteel/Great Designs in Steel... · Taamjeed Rahmaan Kaab Omer. 3 #GDIS | #SteelMatters Overview Background