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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.
30
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
33
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.
35
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???