v

Material Characterization and Modeling of Long Glass-Fiber Composites

Matthew D. Marks, SABIC Innovative Plastics

Society of Plastics Engineers 2009, Troy, MI, USA

2

Contents

1. Why simulations?

2. Fiber orientation prediction

3. Warpage prediction

4. Mechanical analysis

5. Conclusions

3

Why simulations in PP-LGF?

Shorter development cycles + cost pressure:

No more prototypes

=> Virtual prototyping.

-> First time right

65mm65mm

1.26m wide

4

Why simulations in PP-LGF?

Shorter development cycles + cost pressure:

No more prototypes

=> Virtual prototyping.

-> First time right

-> Weight/cost optimization2 kg weight saving and

without metal inserts

5

What is specific for long glass materials?

Fiber orientation

Process

Anisotropic shrinkage Anisotropic Properties

Warpage Mechanical performance

Fiber length distribution

Fiber dispersion

l

%

6

What is specific for long glass materials?

Fiber orientation

Process

Anisotropic shrinkage Anisotropic Properties

Warpage Mechanical performance

Fiber length distribution

Fiber dispersion

most important

should be known,

also effect on

fiber orientation

simulation

prediction

prediction

long glass micromechanics

Mechanical simulation

7

Effect length on fiber orientation and shrinkage

Short glass: highly aligned orientation

Long glass: more isotropic orientation

high width

shrinkage

low width

shrinkage

8

Effect of fiber length on warpage

L

W

Warpage indicator =

Wshrinkage - Lshrinkage

Fiber length

(mm)0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

0 1 2 3 4 5 6

Warp indicator (%) Note: specimen dependent

Shorter fibers:

higher aligned,

more warpage

9

Long vs. Short glass PP 30% - Warpage

ca. factor 3 more warpage for SG-PP

10

Fiber orientation is a function of flow

mould wallsCore: low shear rate,

little effect on orientation

Near walls: high shear rate,

flow orientation.

Flow-channel:

Particle

time Atime B

Stretching induces

circumferential orientation

Core:

SHEAR

EXPANSION

11

=(ar2-1)/(ar2+1)

Fiber orientation prediction with Moldflow

Movie source Charles Tucker

Shear flow Expansion flow

12

Parameters depending on fiber length, fiber dispersion, wall-thickness, etc.

Fiber orientation prediction with Moldflow

=(ar2-1)/(ar2+1)

Default result of Moldflow:

Correct long fiber result:

50% error

in modulus!

validated

correct

results at

SABIC

13

0,0E+00

1,0E+09

2,0E+09

3,0E+09

4,0E+09

5,0E+09

6,0E+09

7,0E+09

8,0E+09

9,0E+09

1,0E+10

E0_31mm E0_107mm E0_183mm E90_31mm E90_107mm E90_183mm

Measurement Locations

E0 & E90 [Pa]

Measured Values

Optimized Values (simulation results with optimazed Ci and Dz)

Default Values (simulation results with Ci and Dz calculated by Moldflow)

Flow length1 2 5 8

Example result shrinkage plate moduli, long fiber condition, t=3mm.

14

Example expansion flow result

At SABIC the Moldflow executable is adapted to give better results

for long fiber, especially for expansion type flows.

See next sheet,

example for medium

fiber length

All conditions

within 5% accurate.

0°

90°

Example measured:4400 MPa

4000 MPa

15

MPI6-Special SABIC MPI6 standard, optimised Ci/Dz

direction change!

flow:4058 4087 MPa

Example difference SABIC MPI versus standard MPI

perp:4062 3952 MPa

outer layer result = average resultSame material properties and interaction coefficients used, example shows effect of different executable.

E1=4400

E2=4000

E1=4400

E2=4000E1=4400

E2=4000

E1=4400

E2=4000

16

CRIMS data – correction for shrinkage

Perpendicular Shrinkage

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

1.4%

1.6%

1.8%

0 5 10 15 20 25 30

Process Condition

MPL Experimental Values

Predicted (With CRIMS)

Predicted (Without CRIMS)

Corrected Residual In-mould Stresses: Correction for things like stress relaxation.

NOTE! For one particular fiber length only!

17

Spring forward - Principle

Straight edge spring forward angle δ =

where:αT thickness = through the thickness CLTE

αT in-plane = in plane CLTE

∆T = cool down temperature range

∆v = crystallisation volume shrinkage

after freezing of flow section.

)vT(

T)vT(

thicknessT

planeinTthicknessT

∆∆α

∆α∆∆αβ

+−

−+ −

1β

δ

18

Spring forward – Current status in Moldflow

Effect is included,

But numerically incorrect. Magnitude may be factor 2 wrong.

- Adapted method in progress (at SABIC)

Tool - shape Product

19

Conclusion for current status warpage prediction

Depending on geometry:

- Yes or No important spring-forward effects :

No Yes

Accurate or predicted warpage factor 2 wrong

(only shape right)

But! Provided the correct long fiber material data are used:

- Fiber length in the product

- Dispersion

- Wall-thickness

etc.

20

Developments in warpage simulations

1. Warpage of both "as molded" and "trimmed" dashboard.

21

Developments in simulations for dashboards/IP-carriers

2. Warpage of assembly in car:

+ vibration welded air ducts, glove box, etc.

How does it fit into the car and when mounted?

Thin-wall dashboard is flexible. Out of the mould shape may be quite different compared to assembled shape.

z-deflection,nice fit

y-deflection,OK in assembly

22

Mechanical analysis - status

- Isotropic analysis

E-modulus or stress-strain curve

- Anisotropic analysis

Use of fiber orientation and micromechanics

Other:

- Optimization

- Crash

- etc.

State of the art

>90%

of all simulations

Only driver is weight saving,

more critical design.

23

Example lock force stiffness, front-end module

24

Deformation movie – lock force test (isotropic result)

25

Analysis options

Abaqus1. Isotropic

2. Anisotropic AbaqusMoldflow

Moldflow Digimat Abaqus

fiber

orientation

micro-

mechanics

mechanical

simulation

In this example the Moldflow triangle mesh is used

26

Micromechanics results

0

2000

4000

6000

8000

10000

12000

0.5 0.6 0.7 0.8 0.9 1

0

0.1

0.2

0.3

0.4

0.5

0.6

E1

E2

G12

nu12

E, G (MPa) ν ()

a11

a22=1-a11

Orientation level

isotropic fully aligned

Digimat results Input:

- Orientation

- Fiber length

- Matrix properties

- Fiber properties

and adaption for

long fiber

Output:

-Youngs modulus

-Shear modulus

-Poison’s Ratio

27

1st Isotropic result

0

100

200

300

400

500

600

700

800

isotropic isotropic

combined

corrections

Moldflow

Abaqus

Moldflow

Digimat

Abaqus linear

Moldflow

Digimat

Abaqus

quadratic

MDAquadr

new Ci/Dz

deformed

mesh

5% thickness

shrinkage

Stiffness (N/mm)

measured result at 2000 N

measured initial stiffness.

Isotropic E-modulus used.

At first sight good agreement.

But! Linear tri-elements used.

Actual wall-thickness thinner

28

Correct isotropic result

0

100

200

300

400

500

600

700

800

isotropic isotropic

combined

corrections

Moldflow

Abaqus

Moldflow

Digimat

Abaqus linear

Moldflow

Digimat

Abaqus

quadratic

MDAquadr

new Ci/Dz

deformed

mesh

5% thickness

shrinkage

Stiffness (N/mm)

measured result at 2000 N

measured initial stiffness.

Correct results need 2nd order elements,

Linear tri's over predict stiffness with 20% here.

ca. 20% lower

29

Anisotropic simulations

Use fiber orientation from flow.

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from fiber orientation to E-moduli

example fiber orientation core layer example E-modulus distribution

31

1st Anisotropic results

0

100

200

300

400

500

600

700

800

isotropic isotropic

combined

corrections

Moldflow

Abaqus

Moldflow

Digimat

Abaqus linear

Moldflow

Digimat

Abaqus

quadratic

MDAquadr

new Ci/Dz

deformed

mesh

5% thickness

shrinkage

Stiffness (N/mm)

AbaqusMoldflow

Moldflow Digimat Abaqus

both: linear tri-elements

ca. 25% too high

32

Anisotropic result with 2nd order elements

0

100

200

300

400

500

600

700

800

isotropic isotropic

combined

corrections

Moldflow

Abaqus

Moldflow

Digimat

Abaqus linear

Moldflow

Digimat

Abaqus

quadratic

MDAquadr

new Ci/Dz

deformed

mesh

5% thickness

shrinkage

Stiffness (N/mm)

2nd order tri-elements

Moldflow Digimat Abaqus

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Anisotropic results – deformed as molded geometry

0

100

200

300

400

500

600

700

800

isotropic isotropic

combined

corrections

Moldflow

Abaqus

Moldflow

Digimat

Abaqus linear

Moldflow

Digimat

Abaqus

quadratic

MDAquadr

new Ci/Dz

deformed

mesh

5% thickness

shrinkage

Stiffness (N/mm)

Moldflow Digimat Abaqus

34

Summary

1st Quick isotropic simulation:

Perfect agreement with measurement.

But!

Simulation was wrong, if correct then 20% under prediction.

Anisotropic simulation gives excellent correlation,

provided that:

- Correct elements at this moment only with Digimat

- Correct geometry look at warpage/shrinkage, etc.

Use of anisotropy gives ca.20% stiffness improvement.

=> Weight saving potential.

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Other analysis types status

- Wall-thickness optimization: state of the art.

- Anisotropic material non-linearity

OK with use of Digimat

And useable, but still under development:

- Anisotropic strain rate dependency

- Anisotropic failure prediction

36

Conclusions

Warpage and anisotropic mechanical simulations for

long fiber PP are state of the art.

But:

A lot of knowledge and material data needed,

see next sheet.

37

What is specific for long glass materials?

Fiber orientation

Process

Anisotropic shrinkage Anisotropic Properties

Warpage Mechanical performance

Fiber length distribution

Fiber dispersion

most important

should be known,

also effect on

fiber orientation

simulation

prediction

prediction

long glass micromechanics

Mechanical simulation

v

Material Characterization and Modeling of Long Glass-Fiber Composites

Matthew D. Marks, SABIC Innovative Plastics

Society of Plastics Engineers 2009, Troy, MI, USA

Questions???