1. Tensile Properties of Individual
Wood Flour Particles
Department of Wood Science and Engineering

2. Introduction
Wood Plastic Composites
Composition:
oWood Particles
oThermoplastics
oPS, PE, HDPE, PP, PVC
oAdditives
composites.wsu.edu/ navy/Navy1/materials.html
Use: outdoor decking, railings, fencing, landscaping http://www.appropedia.org/File:Wood_Plastic_Composite.jpg
timbers, highway infrastructure applications, etc.
Known limitations:
o durability
o significant creep
o thermo-expansion
o weight/strength
o…
Klyosov 2008

3. Motivation
 Space for improvement
o Durability Issues
o Markets
 Improvement strategies
o Trial and Error
 Need more $$
 Need more time
o Virtual Prototyping
 Need better fundamental understanding
– Component properties
– Load transfer between components
 Would existing short fiber composite theory (SFCT) be sufficient to
do this?

4. Background
Short Fiber Composite Theory
http://t2.gstatic.com/images?q=tbn:ANd9GcQRuVQHT1F2XZ5_l3Biw http://www.hindawi.com/journals/jnm/2010/453420/fig1/
GMSgzqaiBTXhakgfKOOtB6gB7itCUqCRZ722N11
http://urbana.mie.uc.edu/yliu/Images/short_fiber_composites.jpg
Assumptions Short Fiber Theory Wood Plastic Composites
Well Defined Geometry
Non-Porous
Well Defined Interface –
Predictable Bonding

5. Background
Short Fiber Composite Theory
measured particle sizes
0.8
Measurements
Particles:
0.6 A
B
C
width, mm
D
0.4
0.2
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
length, mm
O’Dell (1997)
Wang (2007) Hussain (2009)
Assumptions Short Fiber Theory Wood Plastic Composites
Well Defined Geometry
Non-Porous
Well Defined Interface –
Predictable Bonding

6. Background
Short Fiber Composite Theory
Can we apply the
theory to WPC’s?
Assumptions Short Fiber Theory Wood Plastic Composites
Well Defined Geometry
Non-Porous
Well Defined Interface –
Predictable Bonding

7. Objectives and Approach
Objectives
Characterize load transfer between wood particles and the polymer
matrix
Verify the applicability of SFCT to WPCs
Approach
Measure deformation and strain distribution in and around wood
particles embedded in a polymer matrix
Simulate the load transfer with morphology-based material point
method modeling (MPM)
Compare the measurements with MPM and SFTC predictions

8. Strain distribution of embedded wood particles
Specimen preparation
Wood flour added at a 0.25% (OD Compressed in a steel mold to the
weight) loading rate thickness of ~0.6 mm
Pressing temperature (150°C)
Reference: 1.0 mm sections of 0.2 mm
copper wire added at the same rate
Compounded in Brabender Plasticoder Hot pressing @ ~150°C
Unit
Copper Wire - Reference Wood Particle

9. Strain distribution of embedded wood particles
Testing Method
Stereo Microscope ε
Analysis Software
Stepper Motor
F
Field of view ~ 3 mm x 4 mm
Optical resolution ~ 2 μm/ pixel
Load Cell

10. Strain distribution of embedded wood particles
Strain Measurements – Various Angles
Oriented 0° to the
σ11 σ11
direction of loading
Oriented 45° to the σ11 σ11
direction of loading
Oriented 90° to the σ11 σ11
direction of loading

11. Strain distribution of embedded wood particles
Strain Measurements – Multiple Particle Interaction
σ11 σ11
Various Particle-to-Particle Interactions
σ11 σ11
σ11 σ11

12. Strain distribution of embedded wood particles
Strain Measurements - Analysis εxx
0.10
σ11 σ11
0.05
Stress-Strain Wire 0
25.00
20.00
Nominal Stress (MPa)
15.00
10.00
Exx
5.00 0.00
0.00
0.0% 2.0% 4.0% 6.0% 8.0%
Strain

13. Strain distribution of embedded wood particles
Strain Measurements - Analysis εxx
0.10
σ11 σ11
0.05
Stress-Strain Wire 0
25.00
20.00
Nominal Stress (MPa)
15.00
10.00
Exx
5.00 0.00
0.00
0.0% 2.0% 4.0% 6.0% 8.0%
Strain

14. Strain distribution of embedded wood particles
Strain Measurements - Analysis εxx
0.10
σ11 σ11
0.05
Stress-Strain Wire 0
25.00
20.00
Nominal Stress (MPa)
15.00
10.00
Exx
5.00 0.00
0.00
0.0% 2.0% 4.0% 6.0% 8.0%
Strain

15. Strain distribution of embedded wood particles
Strain Measurements - Analysis εxx
0.10
σ11 σ11
0.05
Stress-Strain Wire 0
25.00
20.00
Nominal Stress (MPa)
15.00
10.00
Exx
5.00 0.00
0.00
0.0% 2.0% 4.0% 6.0% 8.0%
Strain

16. Strain distribution of embedded wood particles
Strain Measurements - Analysis εxx
0.10
σ11 σ11
0.05
Stress-Strain Wire 0
25.00
20.00
Nominal Stress (MPa)
15.00
10.00
Exx
5.00 0.00
0.00
0.0% 2.0% 4.0% 6.0% 8.0%
Strain

17. Strain distribution of embedded wood particles
Strain Measurements – Analysis
SFCT
Wire Particle
Similar?
Bonded Length of the Fiber
Wood Particle

18. Strain distribution of embedded wood particles
Strain Measurements – Analysis
Optical Measurement Short Fiber Theory MPM Simulation
ε E
σ τ
100
90
90
80
80
70 Bonded Length of the Fiber 70
60 60
50 50
40
40
30
30
20
20
10
20 40 60 80 100 120 140 20 40 60 80 100 120 140

19. Strain distribution of embedded wood particles
Strain Measurements – Troubleshooting
Film Thickness Artifact
100
90
80
70
Optical Measurement 60
50
40
30
20
10
20 40 60 80 100 120 140
90
80
70
MPM Modeling 60
50
40
30
20
20 40 60 80 100 120 140

20. Strain measurement of individual wood
particles
Sample Preparation
≈ 1.0mm
Adhesive
≈ 0.2mm
Bridge
Wood Particle
Front Profile
Dimensions recorded for nominal stress calculation

21. Strain measurement of individual wood
particles
Testing - Method
F
F
Wood Particle Testing in Tension Optical Measurement

22. Strain measurement of individual wood
particles
Analysis
225.00
Stress (MPa)
150.00
75.00
(εxx)
0.00
0.0% 0.1% 0.2% 0.3% 0.4% 0.5% 0.6% 0.7%
Strain
100
80
Stress (MPa)
60
40
(εxx)
20
0
-0.5% -0.4% -0.3% -0.2% -0.1% 0.0%
-20
Strain

23. Strain measurement of individual wood
particles
Troubleshooting
0.0006
0.0004
Apparent Negative Strain in Tension 0.0002
Strain
0
100
-0.0002
80
-0.0004
Stress (MPa)
60
Wood particle strain under no loading
40
(εxx)
20
0
-0.5% -0.4% -0.3% -0.2% -0.1% 0.0%
-20
Strain
Out of plane movement

24. Strain measurement of individual wood
particles
Troubleshooting
3D DIC Measurement Catadioptric System
Wood particle Right angled
Light path mirror
25 mm
Planar mirror
Camera 1

25. Strain measurement of individual wood
particles
Troubleshooting
“Left” View “Right” View

26. Strain measurement of individual wood
particles
Troubleshooting

27. Conclusions
Good qualitative agreement of strain patterns around the
embedded particle obtained comparing:
• Optical measurements
• MPM modeling
• Short fiber theory
3D DIC of single wood particles is possible
• Single wood particle strain values can be obtained and the
modulus of these particles can be determined.
• Refinement of sample preparation and testing

28. Acknowledgement

29. Questions?