investigation of ahss formability using a customized t-shaped

Investigation of AHSS Formability Using a

Customized T-Shaped Panel with

ex situ DIC

Advanced Engineering, AK Steel Research & Innovation

Dr. Yu-Wei Wang

05.11.2016

• Goal

• ex situ DIC (Digital Image Correlation)

− A New Approach for Deformation Measurement

• AHSS Formability Study

Deformation Modes and Histories

Edge Cracking and Stretch Bending

• Conclusions

OUTLINE

Goal: A Lab Test that Bridges Standard Tests to Actual Stamping

Actual Manufacturing

Deformation Mode

Forming History

Edge Cracking

Stretch Bending

Lab Standard Material

Characterization

• Adjustable die cavity depth

• Adjustable center pocket

Formability Study – T-Shaped Die Design

R

8

Connected to tableConnected to table

Formability Study Using T-Shaped Panel

(mm)

ex situ DIC: A New DIC Approach to Measure Deformation

• Standard DIC method (on-site, in-position) is not

applicable: no access to part through forming die.

• Conventional methods such as ARGUS system or Circle

Grid Analysis are not applicable on the dark surface.

• A new approach of DIC (off-site, out-position) has been

developed at AK Steel for deformation mode and history

study:

ex situ DIC

DIC with 3 Cameras

Major Strain

Minor Strain

AHSS Formability Study - Forming Process

ex situ DIC & Argus

Initial Blanks

With DIC Pattern

(Argus Pattern Covered)

Formed Parts

With DIC Pattern

Formed Parts

with Argus Pattern

Major

Strain

Minor

Strain

Argus*ex situ DIC

Forming evaluation: ex situ DIC vs. Argus vs. FEA

Simulation

*Argus measurement by

1

2

•Material: CR4

•Thickness: 0.7 mm

Thickness Strain

(true)

Thickness

(mm, calculated)

Thickness

(mm, ultrasonic)

Difference

1 -0.08492 0.640558 0.638 0.399%

2 -0.24018 0.531875 0.527 0.917%

ex situ DIC: Validation Using Ultrasonic, Difference Less Than 1%

AHSS Formability Study - Deformation Modes

1

2

3

123

1

2

3

ex situ DIC Reading

1

2

3

123

Simulation Results

The strain history at selected location

FEA (draw depth)

13 mm

10 mm

7 mm

4 mm

Major Strain Minor Strain

1 mm

AHSS Formability Study - Strain Path

13 mm

10 mm

7 mm

4 mm1 mm

Minor True Strain

Ma

jor

Tru

e S

tra

in

ex situ DIC

Reading

Simulation

Results

AHSS Formability Study - Strain Paths of Sections

Strain Unit: 10-3

AHSS Forming Mode Study - Strain Distributions of Sections

Strain Unit: 10-3

AHSS Forming Mode Study - Section Strain Paths

Strain Unit: 10-3

AHSS Formability - History

T-Shaped Panel

Test Measurement

ex situ DIC

Microstructure

FEA Modeling

AHSS Formability Study -

Point 7: Plane Strain

0.64492

(RAVF)Reference 0.66256

(RAVF)

AHSS Formability –Retained Austenite Volume Fraction (RAVF), strain path

Strain Unit: 10-3

* RAVF measurements by PNNL at ANL

Reference Point #7 Change

0.66256 0.64492 -0.02/ -3%

Point 8: Tension-Tension Strain

0.27047

(RAVF)Reference 0.66256

(RAVF)

Strain Unit: 10-3


0.66256 0.27047 -0.39 / -60%


AHSS Formability – Microstructure, strain path

Reference 0.66256

(RAVF)

Point 1: Non-Linear Strain Path

0.4156

(RAVF)

Strain Unit: 10-3


0.66256 0.4156 -0.25 / -37%



Reference 0.66256

(RAVF)

0.58338

(RAVF)

Point 18: Tension - Compression Strain

Strain Unit: 10-3


0.66256 0.58338 -0.08 / -12%



Major Strain

Minor Strain

AHSS Formability - Edge Forming Process

Hole Expansion Ratio:

10.6%

Without hole

With holes

Displacement (mm)

AHSS Formability - Edge Strain

- 0.037, 0.192

Strain Unit: 10-3

AHSS Formability – Edge Strain (Cont’d)

Major Strain Minor Strain

11

44

1

4

RAVF Eff. Strain

Reference 0.66256 -

Pt 4 0.57491(13%) 11%

Pt 1 0.55505(16%) 18%

AHSS Formability - Edge Strain Pattern

ex situ DIC Argus

AHSS Formability - Edge Strain Path

ex situ DIC FEA Simulation

Total Elongation as CriteriaUniform Elongation as Criteria

Edge cracking predicted at 10 mm forming depth

Cracking propagation at 14 mm forming depth

Edge forming at 10 mm forming depth

Edge cracking predicted at 14 mm forming depth

Edge crack initiation predicted for NG980

AHSS Formability - Edge Crack Prediction by FEA

• The NG980 T-Shaped panel with cutouts

was formed.

• Test load-displacement curve shows that

edge cracks initiated at 14 mm forming

depth.

• Both uniform and total elongation of

uniaxial tensile test are used in FEA as

criteria of edge crack prediction.

With total elongation, edge cracking is

predicted to initiate at 14 mm.

With uniform elongation, edge cracking is

predicted to initiated at 10 mm.

edge cracks initiated at

14 mm forming depth

AHSS Formability - Edge Crack Observation in T-Shaped Panel Test

AHSS Formability –Bending

1

2

fracture

CONCLUSIONS

• A T-shaped panel that resembles the top of B-Pillar is selected for

3GAHSS formability investigation. The die is designed by ICME task 3

team and the construction of the die is funded by ICME project.

• ex situ DIC: a new measuring method for deformation is proposed and

used successfully for deformation mode and history of T-shaped panel

forming.

• Together with ex situ DIC, FEA and microstructure evolution, the T-

shaped panel is shown to be effective to study and characterize the

formability of AHSS, including stretch bending and edge cracking.

THANK YOU!

Project Team & Acknowledgements

ICME Task 3 Team Members

(Die Surface) •Chang Du, FCA US LLC

•DJ Zhou, FCA US LLC

•Rick Johnson, FCA US LLC

•Evangelos Liasi, Ford Motor Company

•Yinong Shen, Ford Motor Company

•Feng Ren, Ford Motor Company

•Constantin Chiriac, Ford Motor Company

•Raj Sohmshetty, Ford Motor Company

•Gene Hsiung, General Motors Company

•Tom Stoughton, General Motors Company

•Ken Schmid, General Motors Company

•Lou Hector, General Motors Company

•John Carsley, General Motors Company

•Weiping Sun, Nucor Corporation

•Dean Kanelos, Nucor Corporation

•Hong Yao, ArcelorMittal USA LLC

•Sriram Sadagopan, ArcelorMittal USA LLC

•Eric McCarty, Auto/Steel Partnership

•Feng Zhu, Ak Steel

•Yu-Wei Wang, AK Steel

Project Team Members

•Wei Wu, Ph.D.

•John Panagiotis Makrygiannis

•Feng Zhu, Ph.D.

•Yu-Wei Wang, Ph.D.

Die Structure Design and Argus Measurement by

Ford Motor Company

• Dr. E. Liasi, Y. Shen, L. Huang, G. Kluczynski,

DIC Technical support by Oakland University

• Prof. Lianxiang Yang, Xinfeng Shi, Hao Wang

Phase Volume Measurement by PNNL

• Dr. Xin Sun, Dr. Xiaohua Hu

Q & A

Investigation of AHSS Formability Using a

Customized T-Shaped Panel with

ex situ DIC

investigation of ahss formability using a customized t-shaped

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