20 flange shear affected zone study

Flange Shear Affected Zone Study

Ken SchmidGeneral Motors Corp.

Auto Steel

Partnership

w w w . a u t o s t e e l . o r gw w w . a u t o s t e e l . o r gw w w . a u t o s t e e l . o r gw w w . a u t o s t e e l . o r g

General Motors Corp.

Xin Wu, Ph.D.Wayne State University

Acknowledgements

• Wayne State University

• General Motors Corp.

• Chrysler LLC

• Ford Motor Company

• Former Ronart


• Former Ronart

• United States Steel Corp.

• Arcelor Mittal

• Nucor Steel

• Severstal N.A.

• AK Steel Corp.

Edge Fracture with DP Materials

Challenges:

• AHSS is sensitive to edge cracking.

Mechanical trimming changes the edge

microstructures and properties, which affects


microstructures and properties, which affects

fracture during flanging, or stretch drawing.

• Predicting fracture is difficult.

Edge Fracture with AHSS

FEA Predicted

Actual Edge Cracking


• Conventional FEA often fail to predict edge fracture based on FLC;

• FEA procedure and failure criterion need to be improved.

Severity of Fracture

HSLA

DP980


Die trimmed blank had severe splittingLaser Trimmed blank had no splits

Task and Objective

Task

• Characterize the shear-affected zone after

mechanical trimming and after flanging, for

three DP steels and with various flanging

length.

Objective


Objective

• Provide an experimental foundation for

understanding the edge deformation and

fracture during trimming & flanging

• 2 parts: round-hole & multi-shaped

• 3 materials: DP600, DP780, DP980

• 3 flange lengths: 1mm, 3mm, 5mm

• 2 die clearances: 10%t, 15%t

• 2 trimming methods (mechanical & laser trimming)

Trimming & Flanging Experiments


Round HoleMulti-shaped Hole

Various corner radii

Rollover

Burnish

Fracture

Rollover

Burnish

Fracture

Burr

Rollover

Burnish

Fracture

Burr

Sheared Edge: Four Zones

HSLA

Image provided by USS


AHSSRollover

Burnish

Fracture

Burr

Reduced

Rollover

Burnish

Burr

Enlarged

Fracture zone

Image provided by USS

Edge Characterization 1:

Obtain Four Edge Zone Heights

Methods used:

• OM

• SEM

• Replica

Direct Observation with Optical Microscopy (OM)

Back light

Artificial notch

Sample on a magnet

holdert0


Front light

Reflected light

Image

on the focus plane Roll-over

Burnish

Fracture

Sheared edge

Burr

Image Process and Zone Height Calculation

Roll-over Zone

Burnish Zone

Fracture Zone

Burr Zone

t0


Procedure:

• Obtain edge image

• Trace edge

boundaries

• Fill-in colors

• Obtain Mean and

Std. Deviation over a

few thousand points

along the edgeUser software (Matlab):

scan pixels & calculate zone heights

Factors affecting edge profiles

y = -0.106x2 + 0.0771x + 0.7227

y = 0.1071x2 - 0.0848x + 0.2039

0%

20%

40%

60%

80%

100%

Rela

tive Z

on

e H

eig

ht,

%t

(a)

Fracture Burnish

Roll-over Relative

y = 0.0125x2 + 0.0164x + 0.2336

y = -0.0167x2 + 0.0039x + 0.6909

0%

20%

40%

60%

80%

100%

Rela

tive Z

on

e H

eig

ht,

%t

(b)

Fracture Burnish

Roll-over Relative

y = -0.0144x + 0.6811

y = 0.0099x + 0.2456

0%

20%

40%

60%

80%

100%

Rela

tive Z

on

e H

eig

ht,

%t

(c)

Fracture Burnish

Roll-over Relative

Die Clearance RD vs. TDMaterial Strength


y = -0.0011x2 + 0.0077x + 0.0734

y = 0.0032x2 + 0.0046x + 0.0098

0%

5%

10%

15%

-1.5 -1 -0.5 0 0.5 1 1.55%t 10%t 15%t

Relative Die Clearance

0%

-1.5 -1 -0.5 0 0.5 1 1.5

y = 0.0042x2 - 0.0203x + 0.0755

y = -0.0044x2 - 0.0014x + 0.0156

0%

5%

10%

15%

-1.5 -1 -0.5 0 0.5 1 1.5

600 780 980

Material Strength, MPa

0%

-1.5 -1 -0.5 0 0.5 1 1.5

y = 0.0045x + 0.0733

y = 0.0023x + 0.0116

0%

5%

10%

15%

-1.5 -1 -0.5 0 0.5 1 1.5

RD TD

Shear Direction to RD

0%

-1.5 -1 -0.5 0 0.5 1 1.5

)(2

1)(''

''1

12

1

12

12

0xx

xxxx

xx

xxxx −

−+−=−

−

−+=

Edge Characterization 2: Obtain Edge Pre-Strain Distribution

00 ≈∂

∂⇒≈

y

wu

∂

∂

∂

∂+

∂

∂+

∂

∂=

j

k

i

k

j

i

i

j

ijx

u

x

u

x

u

x

uE

2

1

α2

2

tan5.02

1=

∂

∂=

x

wExx

αtan5.02

1=

∂

∂=

x

wExz

αααα

αααα


0.01

0.1

1

10

100

0 30 60 90

Tilting Angle (deg)

Str

ain

s

Exx

Exz

Eeff

2 ∂x

= ijijeff EEE3

2

αααα

z (

mic

ron)

800

1000

1200

1400

1600

z (

mic

ron)

800

1000

1200

1400

1600

40

50

60

Effective Strain

z (

mic

ron)

800

1000

1200

1400

1600

2

2.5

3

3.5

4

4.5

Measured Shear Angle and

Converted Strain Distribution


• Example: DP980-15%-RD

x (micron)

z (

mic

ron)

0 5000

200

400

600

x (micron)

z (

mic

ron)

0 5000

200

400

600

10

20

30

x (micron)z (

mic

ron)

0 5000

200

400

600

0.5

1

1.5

2

Localiz

ed N

eckin

g

Crack-microstructure interaction:

Diffu

se N

eckin

g

Necking control Fracture controlNecking control Fracture control

Decreasing Length Scale of Process Zone

Forming Limit


Localiz

ed N

eckin

g

Crack-microstructure interaction:

Diffu

se N

eckin

g

>10mm(Stamping part)

1-10mm

Edge crack/roughness: 1-100 µm

Cluster of martensite: 10-100 µm

Grain/phase particle: 1-10µµµµm

Dislocation clusters: 1nm-0.1µm

Precipitates: 1-100nm

GB/Interface: 0.1-1nm

Lattice constant of Fe: 0.287nm

Great challenge to predict fracture controlled forming limitGreat challenge to predict fracture controlled forming limit

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Tru

e S

train

Eeff

Ex

Exz

Ez

Ey

Eeff,o

Ex,o

Exz,o

Ez,o

Ey,o

(a) Top/Edge Element

Hole

Piercing

Hole

Expansion

0.4

0.6

0.8

Ho

op

(M

ajo

r) S

train

, E

y

With Pre-Strain

(Switch Axes)

Without Pre-Strain

FLC

Hole Expansion

at Top-Edge of the Hole

FEA: with & without Edge Pre-strain

Hole Piercing Hole Expansion

No pre-strain


-1.5

0 10 20 30

FEA Increment

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

0 10 20 30

FEA Increment

Tru

e S

train

(b) 0.4t From Top/Edge Element

Hole

Piercing

Hole

Expansion

-0.4

-0.2

0.0

0.2

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8

Radial (Minor) Strain, Ex

Hole Piercing

Piercing + Expansion

Piercing + Expansion (switch axes)

Expansion without Pre-Strain

Measure FLC for DP780

With Pre-Strain

from Piercing

Piercing

M. Chen, C. Du, X. Wu, S Liu, X. Zhu, SD Liu, IDDRG 2009

1. Obtain constituents’ distribution patterns and properties:

– Properties of individual constituents

– Micro structural distribution parameters and patterns

– Edge defect/damage parameters

2. Microstructure representation: constituents’ properties:

Meso-Scale

BridgeMicro-mechanics Continuum mechanics

A Microstructure-Based Stochastic Model


2. Microstructure representation: constituents’ properties:

– Define meshes (scales): The element (ferrite or martensite) is

the smelliest constituent volume

– Re-construct microstructures in critical region

3. Computing with conventional FEA procedure.

– Structural instability and localized necking at small scale (no

limit strain)

– Fracture in matrix, reinforcement, or at interface

400

600

800

1000

1200

1400

Tu

e S

tre

ss

(M

Pa

)

DP600-0 DP600-45 DP600-90

DP600

DP780

DP980

Tensile Test


Grade

YS

(MPa)

UTS

(MPa)

UE

(%)

TE

(%)n-value r-value

DP600 367 611 16.5 25.3 0.18 1.04

DP780 496 830 11.9 18.2 0.12 1.07

DP980 608 1064 7.7 12.5 0.09 1.10

0

200

0 5 10 15 20 25 30

True Strain (%)

DP600-0 DP600-45 DP600-90

DP780-0 DP780-45 DP780-90

DP980-0 DP980-45 DP980-90

Optical Micrographs

DP600

RD

t

RD

TD

TD

tSide View Top View Front View

Martensite:

13.7%


DP780

DP980

35.0%

47.3%

22

.8m

m

USAMPA/SP’08 Tensile Behavior & Model Calibration

200

400

600

800

1000

1200

En

g. S

tre

ss

(M

Pa

)

Simulation

Exp'l

YS n-value

Martensite 620 MPa 0.19

0

500

1000

1500

2000

2500

3000

0.0 1.0 2.0 3.0

True Strain

Tru

e S

tre

ss

(M

Pa

)

Martensite

Ferrite

[1] W. N. Liu, K. S.

Choi, X. Sun, M. A.

Khaleel, Y. Ren, N.

Jia, and Y. Wang,

SAE 2008-01-1114.

Fitted


6.35mm

22

.8m

m

Thickness 1.0mm, Element size : 0.1mm × 0.1mmTotal element #: 14,592, Dynamic Explicit

YSM : YSF 1.22, 3.33, 3.92

N-Element 14592, 4,608, 1480, 912

M-v%, measured 16v%/25v%/46v%

FEA algorithm Explicit (CPS4R, S4R)

Process Tensile, Piercing, Flanging

Ferrite

Martensite

0

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Eng. Strain

Exp'l Ferrite 510 MPa 0.12

Parametric Study:

Necking Evolution vs. Effective Strain

DP980


0 5% 8% 10% 11.3% 11.7% 12.5%

Unified Model: Variable Martensite vol%

0

200

400

600

800

1000

1200

0.00 0.05 0.10 0.15 0.20 0.25

Eng. Strain

Eng. S

tress (

MP

a)

Exp. DP600

Calib. DP600

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2 0.25

Eng. Strain

Eng. S

tress (

MP

a)

Exp. DP780

Calib. DP7800

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2 0.25

Eng. Strain

En

g.

Str

es

s (

MP

a)

Exp. DP980

Calib. DP980

DP980 DP780 DP600


Stochastic Microstructure Reconstruction

2

0Err f f + = − → ∑ %

DP780DP780

• Two-point probability function for M-particle spacing + Lineal-path probability

function for M-particle connectivity


,0

i i REV

n

Err f f + = − → ∑ %

Total n pixels

Predicted elongation to failure:

• TD < RD;

• Segregated < Random

The effects of Martensite size and

preferred orientation are predicted

without introducing material property

assumption.

Bi-Mat’lBi-Material Model

Von Mises Strain: Bi-Mat’l vs. Monolithic


Monolithic

Bi-Material Model

Equivalent Strain: Initial and FinalDP 600 DP780 DP980

1-mm

3-mm

5-mm

Implementation to Stamping

(Flanging)


Pierced hole ID=10.8mm, Punch OD=18mm, Die ID=21.52mm, Fillet Radius = 3.0mm, Bland OD=70mm, Thickness=1.66mm.

1-mm

3-mm

5-mm

Summary

1. Trimmed edges were characterize by (3x3x2) Design of Experiment

The sensitivity of these effects needs to be further quantified.

With decreasing:

•die clearance,

•material strength,

•trim line angle to RD

Roll-over zone height decrease (less clear)

Burnish zone height increase

Fracture zone height decreases

Burr height reduces

More edge strain hardening and less defects;

Reduce tendency of edge cracking


The sensitivity of these effects needs to be further quantified.

2. Strain distribution in trimmed edge zone is measured based on metal

flow line tilting angle and finite strain formulation

3. Edge fracture modeling capability can be improved by

– FEA with homogeneous properties but consider shear-induced

pre-strain

– A microstructure-based meso-scale composite model using

constituents’ properties and distribution patterns (new)

Date post:	16-Jun-2015
Category:	Documents
Upload:	nakul-surana
View:	244 times
Download:	0 times

20 flange shear affected zone study

Documents