Finite element analysis of central bursting defects

occurring in cold forward extrusion

1) Graduate student of Gyeongsang National University(GNU), Jinju / Korea; 2) Korea Institute of Industrial Technology, Incheon / Korea; 3) Youngsin Metal Industrial Co., Ltd. Pyeongtaek / Korea; #) School of Mechanical and Areospace Engineering, GNU, Jinju / Korea, msjoun@gnu.ac.kr

MSEC2011, June 14, 2011

MS Joun #), MC Kim 1), DJ Yoon2) , HJ Choi2), YH Son3)

www.afdex.com

AFDEX

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Contents

⊙ Research background

⊙ Examples of central bursting defects

and finite element predictions

⊙ Application of finite element analysis to tensile test

⊙ Scheme of analyzing crack propagation

⊙ Finite element analysis of fracture phenomena in tensile test

⊙ Finite element analysis of the central bursting defects

⊙ Conclusions

Research background – Forging defects

Hot shortness

Metal flow Buckling

Shape defect

Folding

Under-filling

Air-trapping

Piping

Ductile fracture

Bad spheroidizing

Chevron crack

Research background

⊙ Chevron defect has been well known and found at times

⊙ Chevron defects may lead to big accidents.

⊙ High strength-low strain hardening material is exposed to chevron defects.

⊙ Survey of the literature

○ Jennison, design parameters

○ Avizur, relatively small load/ Coulomb friction, die angle and reduction area

○ Kachanov, crack generation criterion

○ Soyarslan, et al., micro-voids, macro-crack

○ McAllen, et al., safe reduction ratios below 7%/ die land effect

○ Many researches have obtained finite element predictions of chevron crack

propagation, but most research works are different from actual experiments.

Previous studies on central bursting defects

C. Soyarslan et al.

ABAQUS/ Explicit

Elasto-plastic

K. Saanouni et al.

Forge

Elasto-plastic

H. Cho et al.

DEFORM

Labergeere et al.

ABAQUS/ Explicit

thermoelasto-viscoplastic

F. Ahmadi et al.

Rigid-plastic

McAllen et al.

ABAQUS

EXPERIMENTS

PREDICTIONS

Extrusion Drawing

cr

or100c

o

rr

r

81r

90r 78r 84r

72r 38r 67r 55r 60.0r 50r

83meanr

Previous studies on material identification

⊙ K. Komori, 2002, Simulation of tensile test by node separation method.

○ Axi-symmetric, Rigid-plastic.

○ Fracture load

1 2

(1 ) (1)

(1 ) (2)

kk

kk

f f A

f f B B

⊙ Eduardo E. Cabezas, Diego J. Celentano, 2004, Experimental and numerical analysis of

the tensile test using sheet specimens, SAE 1045 steel.

Cylindrical specimen Sheet specimen

New approach to material identification by tensile test

Elongation [mm]

Te

nsile

loa

d[k

N]

0 2 4 60

2

4

6

8

10

12

14

Measured

Prediction

Necking

point

Fracture

point

7.94

0x

0xy

0y

0yx

1/ 60mm/sy

0yx

( ) 0n

xt( ) 0n

yt

x

y

Gage

mark

Gage

mark

MS Joun et al., 2008, Mechanics of Material

-Material: SWCH10A

-Cylindrical specimen

-Iterative approach

-Rigid-plastic FEM

-Strength coefficient = function of strain

-Strain-hardening exponent

= true strain at the necking point

1.608E+0

1.407E+0

1.206E+0

1.005E+0

8.042E-1

6.032E-1

4.021E-1

2.011E-1

1.673E-7

Damage just before fracture

DCr=1.68

Elongation (mm)

Te

nsile

loa

d(N

)

0 2 4 6 8 100

5000

10000

15000

20000

25000

30000

35000

SCM435

ESW95

ESW105

⊙ Tensile load-elongation curves ⊙ True stress-strain curves

True strain (mm/mm)

Tru

estr

ess

(MP

a)

0 0.4 0.8 1.2 1.60

200

400

600

800

1000

1200

SCM435

ESW95

ESW105

Applications of the new approach to material ID

Engineering strain (mm/mm)

En

gin

ee

rin

gstr

ess

(MP

a)

0 0.1 0.2 0.3 0.40

200

400

600

800

1000

1200

Experiment (SCM435)

Analysis (SCM435)

Experiment (ESW95)

Analysis (ESW95)

Experiment (ESW105)

Analysis (ESW105)

Applications of the new approach to material ID

Verification of predictions

PredictionExperiment

SCM435 ESW105

Non-contacted Contacted Non-contacted Contacted

By AFDEX

A general-purpose metal forming simulator based on rigid or elasto-thermoviscoplastic FEM

Research objective

○ Suggestion of an improved approach to finite element prediction

of central bursting defects.

-Rigid-plastic FEM

-Improved node separation scheme

-Damaged element removal scheme

○ Parametric studies for revealing the effects of process design

parameters on the chevron defects.

-Effect of reduction of area

-Effect of die conical angle

-Effect of friction

-Effect of strain-hardening exponent

An improved element split scheme

Step 1. Set i=0

Step 2. Select the most damaged element ⓘ

Step 3. Find the most damaged edge ⓘ on the boundary of the element ⓘ

Step 4. Set i=i+1 and go to Step 2

I

J K

Komori first applied the element split scheme

Element elimination or degredation schemes

②

① ②

③

① ②

③

①

③ ④

④

Komori Present

Before After

Damaged element cleaning scheme

Damage model used

1

0

f

D d

0

f

D d

McClintock damage model

Special case of McClintock damage model, employed in this study

1.0, / 2n

2.13E-001

1.46E-001

7.96E-002

1.30E-002

C L

1.52E+000

1.23E+000

7.84E-001

4.89E-001

3.42E-001

1.23E-002

Metal flow Distorted mesh Damage Effective strain

Example

1 3 1 32

sinh[ 3(1 ) ]3(1 )

nn

Cases of extrusion process designs, simulated

Finite element model Punch

Die

● Workpiece size: Φ14.0 mm × h 28.7 mm ● Strain hardening exponent: 0.14 ● Critical damage: 0.20 ● Initial mesh size: 0.2 × 0.2mm ● Number of quadrilateral elements: 4862

Workpiece

Angle, α [ º] Reduction of area, R.A. [%] Coefficient of

Coulomb friction, μ

Case 1 30 18 0.03

Case 2 60 18 0.03

Case 3 30 30 0.03

Case 4 30 18 0.05

2

Angle, α [ º] Reduction of area, R.A. [%]

Coefficient of Coulomb friction,

μ R.A 60 18 - 39 0.05

Conical angle 30 - 100 25 0.03

Friction 60 30 0.01 - 0.1

General cases

Parametric studies

General cases

(a) Case 1 (b) Case 2 (c) Case 3 (d) Case 4

30, 18,

0.03

60, 18,

0.03

30, 30,

0.03

30, 18,

0.05 αº, R.A.%,

μ

82r 89r 68r 87r

82meanr

Effect of reduction of area (α=60º, μ=0.05)

R.A.=18.0 R.A.=25.0 R.A.=30.0 R.A.=39.0

87r 86r 77r 55r

Experimental results of Zimerman et al. [22].

When R.A. is greater than a certain value, the smaller R.A., the more dangerous

Effect of die angle (R.A.=18%, μ=0.03)

α= 30º α= 60º α= 80º α= 100º

82r 89r 87r 82r

Similar numerical results for die conical angles of less than 60°

by Saanouni et al. [4]

The same as experimental research works of Zimerman et al. [22]

and numerical study of Aravas [23].

Effect of friction (α= 60º, R.A.=18%)

010.μ 050.μ 100.μ . 0 15μ

92r 87r 86r 0r

Similar numerical studies by Saanouni et al. [4] and Soyarslan et al. [5]

Conclusions

⊙ A new scheme of predicting crack propagation was presented. -An improved element split -A critical case of Mcklintock’s damage model

-Rigid-plastic FEM -Damaged element cleaning scheme ⊙ Central bursting defect was successfully simulated by the new scheme. -The normalized crack radius, ratio of chevron defect’s radius to extrusion

radius is large compared with other researches -Defect shape is also different from others ⊙ Effects of Coulomb friction, die angle and reduction of area were investigated. -Nearly the same as the previous stuides, but they are so complicatedly coupled that additional studies should be accomplished.

○ Material: SWCH10A

○ DCr=1.68

A

C B

12.5slope

0.002

12.5slope

0.002

Recent work on fracture prediction in tensile test

O

Elongation [mm]

Te

nsi

lelo

ad

[kN

]

0 1 2 3 4 5 6 7 8 90

2

4

6

8

10

12

ExperimentPrediction

A

C

B

O

B

C

O A B

Damage model used

1

0

f

D d

0

f

D d

McClintock damage model

Special case of McClintock damage model, employed in this study

1.0, / 2n

2.13E-001

1.46E-001

7.96E-002

1.30E-002

C L

1.52E+000

1.23E+000

7.84E-001

4.89E-001

3.42E-001

1.23E-002

Metal flow Distorted mesh Damage Effective strain

Example

1 3 1 32

sinh[ 3(1 ) ]3(1 )

nn

Effect of die conical angle on damage

Half die conical angle (degree)

Ma

xim

um

cu

mu

lative

da

ma

ge

0 10 20 30 40 500

0.1

0.2

0.3

0.4

0.5

0.6n=0.001

n=0.05

n=0.10

n=0.15

n=0.20

n=0.25

30%R.A. =

30

Reduction of area (%)

Ma

xim

um

cu

mu

lative

da

ma

ge

0 10 20 30 40 500

0.1

0.2

0.3

0.4

0.5

0.6n=0.001

n=0.05

n=0.10

n=0.15

n=0.20

n=0.25

Effect of reduction of area on damage

Half conical angle =

Effect of friction on damage

Friction coefficient

Ma

xim

um

cu

mu

lative

da

ma

ge

0 0.05 0.1 0.15 0.20

0.2

0.4

0.6

n=0.001

n=0.05

n=0.10

n=0.15

n=0.20

Coefficient of Coulomb friction

30%R.A. = 30Half conical angle =