evaluation of durability in wood-plastic composites using...
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Evaluation of Durability in Evaluation of Durability in WoodWood--Plastic Composites Plastic Composites Using XUsing X--ray Tomographyray Tomography
Lech Lech MuszyMuszyńńskiskiBrian K. BayBrian K. BayJohn SimonsenJohn SimonsenYu GengYu GengYi WangYi Wang
Intertech 2005
Outline
Background and introduction to XMTExperimental setupResultsConclusionsAcknowledgements
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Wood flour in HDPE
0.1 mm
0.3 mm
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WoodWood--Plastic Composites (WPCs)Plastic Composites (WPCs)
Mechanical and physical properties of WPCs may be engineered by changing phase characteristics, proportions and orientation, processing parameters, and internal bonding
Limitations: composite design is limited by the naturally variable wood properties and the limited selection of thermoplastics that may be used with wood (melting temperature <200° C)
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Focus on the Internal BondFocus on the Internal Bond
Challenge: Bonding two dissimilar materials
Hydrophilic wood
Hydrophobic thermoplastics
Facilitated by formulation, processing and coupling agents
Improve mechanical properties
Improve water sorption and durability
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How much can flexural tests reveal about internal bonding?
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WPC micromechanicsWPC micromechanics
Durability and mechanical performance of WPCs are decided on the µ-mechanical level - in the interphase between wood and plastic
Traditional testing methods offer indirect and limited insight to µ-mechanical performance, µ-damage accumulation and governing failure mechanisms –new methods are needed
Any significant progress in this field depends on better understanding of the composite performance and internal bond durability on the µ-mechanical level, and reliable modeling based on that understanding
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OBJECTIVE
To develop experimental procedures for multi-scale evaluation of micro-mechanical performance, governing failure mechanisms and micro-damage accumulation in WPCs
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Experimental questions
Where does the damage take place?
Statistical characterization of the local deformation and internal damage accumulation
How bad is it?
Correlations between the internal damage and the storage modulus
When will it happen?
Accelerated aging
Samples from the field
Predictive models
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Procedure:Multi-scale analysis
Macro level: elastic modulus, static strength, storage modulus, original and aged (meters)
Optical DIC analysis to identify strain concentrations on the specimen surfaces (mm)
Digital Volume Correlation based on low resolution CT scans (20 µm/pxl) to identify internal strain concentration areas of interest
High Resolution CT scans (3 µm/pxl) on those areas identified in the previous steps to reveal and characterize internal damage concentrations
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Damage characterization
Damage is defined as a degradation in microstructure due to an external or internal influence.
mechanical stress
moisture/temperature cycling
chemical changes
Define damage variable, D, such that E = E0(1 - D)
Nondestructive X-Ray Microtomography
Nondestructive measurement allows evaluation of the three-dimensional internal structure before and after the degrading treatments
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X-ray Microtomography: Measurement principles
• 3D maps of x-ray absorption reconstructed from projection images
• High resolution through high performance x-ray source and detector
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Nondestructive 3-D X-ray microtomography
Is it good for more than just cool pictures?oak
2 mm
oak
2 mm2 mm
LVL (transverse plane),aspen
2 mm
LVL (transverse plane),aspen
2 mm2 mm
plywood, birch
2 mm
plywood, birch
2 mm2 mm 5 mm
OSB
5 mm
OSB
1 mm
Oak Oak vessels
side
topfront
top
right side
back
1 mm1 mm1 mm
Oak Oak vessels
side
topfront
top
right side
back
1 mm1 mm
oak LVL plywood OSB
?1 mm
WPC: Wood/PP
1 mm1 mm
WPC: Wood/PP FRP: E-glass/urethane
2 mm
FRP: E-glass/urethane
2 mm2 mm
FRP: E-glass/epoxy
2 mm
FRP: E-glass/epoxy
2 mm2 mm
Who’s next?Wood/PP GF/Urethane GF/Epoxy
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Nondestructive 3-D X-ray microtomography
Is it good for more than just cool pictures?
Digital tools are available to identify visible features and different material phases (solid phases, voids etc.), quantify connected pore structure, and visualize complex microstructure
Internal strains can be evaluated (Digital Volume Correlation)
Digital Image Correlation Digital Volume Correlation
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Types of Image Correlation
In-plane deformations from single-camera surface images (2D)Out-of-plane deformations from multiple-camera surface images (3D, Poisson’s ratio)Volumetric deformations from tomographic data sets (Digital Volume Correlation)
A 3D extension of DICApplicable to materials with inherent texturePorous materials, composites, large-scale microarchitecture
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Integrated Testing and ImagingDetector Sample Stage X-ray Source
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Hardware Details
The x-ray source:FeinFocus 160 kVp10 micron focal spot
The detector:Thompson TH9438HX image intensifier Retiga 1024x1280 10-bit CCD, lens coupled
The sample stage:Newport RV120 high load rotational stages, opposedInstron 4444 load frame, 2000N capacity
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Software DetailsImage collection:
Field of view between .5 and 10 cm 1000 projections (360 degrees) @ 4 sec/ea
Reconstruction:Feldkamp-style filtered back-projection~ 1billion voxels, res. range 5 - 100 µm
Data volumes:Projection images ~ 2GB, reconstruction volumes ~1 GBCollection ~ 3 h (PC/GPIB based)Reconstruction (2 vols) ~14 hrs (2 Sun processors)
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Volumetric Strain Measurement – How it works
Strain is quantified using correlation methods that compare loaded and unloaded data volumes.
3. Texture Correlation in 2D
1. Marker Tracking in 2D 2. Speckle Metrology in 2D
4. Texture Correlation in 3D
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Strain Measurement - Details
Displacement Vectors Measured at Many Points
Throughout a Sample
Strain Tensors Calculated at Each Point From Groups of Displacement Vectors
INITIAL EXPERIMENTS
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Component Materials
Wood flour
40 mesh pine from American Wood Fibers
Oven dried prior to use for 24 hours at 103°
Plastic
High Density Polyethylene: BP Solvay B53 35H FLK, melt flow = 0.49 g/10 min
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Blending
Brabender Intelli-Torque Plasticorder
Melt HDPE at 170° CAdd gold n-spheresAdd wood flourMix 10 minRemove and store for compression molding
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Pressure molding
Carver Press
Mold: 101.6 x 101.6 x 2 mmTemperature: 185o CPreheat time: 10 minPress time: 10 minPress pressure: 344.8 kPaCooling pressure: 344.8 kPa
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PARTICLE CHARACTERIZATION
Perticle Area Distribution
0
50
100
150
200
0.02
0.04
0.06
0.08 0.1 0.12
0.14
0.16
more
Area [mm]
Cou
nt
Particle Aspect Ratio Distribution
0
25
50
75
100
1.5 2 2.5 3 3.5 4 4.5 5more
Aspect Ratio
Cou
nt
Particle Area Distribution
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Specimens
10 specimens for each wood-PE composite boardSpecimen size
L: 54.5 ±2.0 mmW: 12.5 ±2.0 mm(w: 9.2 ±0.1 mm)t: 2.6 ±0.5 mm
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Density profiles
Wood cell 1.5 g/cc
HDPE 0.95 g/cc
PVC 1.3 to 1.58 g/cc
PP 0.9 g/cc
Wood particles and the polymer matrix materials have similar densities and x-ray absorption levels (CHO).
CONTRAST PROBLEM
1 mm
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GOLD NANOSPHERES
HAuCl4 in water Two phase system: water/toluene
(C8H17)4N+ Br- Gold moves to toluene phaseRemove aqueous phase
Metallic gold precipitatesas spheres, 2 – 5 nm diameterNaBH4
Centrifuge to remove gold nano-spheresAdd to HDPE in Brabender Plasticorder mixer
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Enhanced CT contrast:with a price tag…
MOE [GPa]
0
1
2
3
control 0.1% gold 1% gold
MOR [MPa]
0
10
20
30
40
control 0.1% gold 1% gold
density [g/ccm]
0.0
0.3
0.6
0.9
1.2
control 0.1% gold 1% gold
Property change comparison
0%
20%
40%
60%
80%
100%
control 0.1% gold 1% gold
MOEMOR
density
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Enhanced CT contrast
Ref1%Au
0.1%Au
Ref1%Au
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Enhanced CT contrast
Ref1%Au
0.1%Au
Reconstruction of a longitudinal
section20 µm/voxel
1%Au
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Static tensile tests
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Static tensile tests
0
4
8
12
16
0 0.01 0.02 0.03 0.04 0.05 0.06
Strain, -
Stre
ss, M
Pa
#1#2#3
E* UTS
# MPa MPa
1 1755 14.80
2 1934 14.68
3 1527 12.71
*linear fit to a section of non-linear data
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Static tensile tests: nonlinearity
Etan* E 1%*
# MPa MPa
1 3131 487
2 3846 481
3 2776 387
0
500
1000
1500
2000
2500
3000
3500
0 0.005 0.01 0.015 0.02
Strain, -
E, M
Pa
#1#2#3
*from exponential fit to E(eyy) data
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Static tensile tests: nonlinearity
0
4
8
12
16
0 0.01 0.02 0.03 0.04 0.05 0.06
Strain, -
Str
ess,
MPa
#1#2#3
Etan* E sec1% E sec2%
MPa MPa
721
731
629
1221
1242
1082
E1%*
# MPa MPa
1 3131 487
2 3846 481
3 2776 3870
500
1000
1500
2000
2500
3000
3500
0 0.005 0.01 0.015 0.02
Strain, -
E, M
Pa
#1#2#3
*from exponential fit to E(eyy) data
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Static tensile tests: Poisson effect
ν0%* ν2%*
# - -
1 -0.3516 -0.2959
2 -0.3597 -0.3033
3 -0.3412 -0.2805
*linear fit to a section of experimental data (0.5% - 2.5% strain)
Poisson effect
-0.4
-0.3
-0.2
-0.1
0
0% 2% 4% 6% 8%
ε yy, %
εxx/εy
y, -
#1#2#3
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Degrading procedure
Degradation Procedure, Spec#09
0
100
200
300
400
0 120 240 360 480 600 720 840 960
time, s
load
, N
0.010.00 window 15x15
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Degrading procedure
0.010.00 window 15x15
WPC #1 & #6
0
4
8
12
16
-0.01 0 0.01 0.02 0.03 0.04 0.05
avg strains, -
Stre
ss, M
Pa
#1#06
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D e g r a d a t i o n P r o c e d u r e , S p e c # 0 9
0
1 0 0
2 0 0
3 0 0
4 0 0
0 1 2 0 2 4 0 3 6 0 4 8 0 6 0 0 7 2 0 8 4 0 9 6 0
t i m e , s
load
, N
150 N 175 N 200 N 225 N
0.0050.00 window 15x15
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D e g r a d a t i o n P r o c e d u r e , S p e c # 0 9
0
1 0 0
2 0 0
3 0 0
4 0 0
0 1 2 0 2 4 0 3 6 0 4 8 0 6 0 0 7 2 0 8 4 0 9 6 0
t i m e , s
load
, N
250 N 275 N 300 N 325 N
0.0100.00 window 15x15
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D e g r a d a t i o n P r o c e d u r e , S p e c # 0 9
0
1 0 0
2 0 0
3 0 0
4 0 0
0 1 2 0 2 4 0 3 6 0 4 8 0 6 0 0 7 2 0 8 4 0 9 6 0
t i m e , s
load
, N
350 N 375 N ultimate
max = 0.015 max = 0.020 max = 0.035
Consistent weak areas…
strain
max0.00 window 15x15
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Degrading procedure
0.0350.00 window 15x15
Degradation Procedure, Spec#06
0
4
8
12
16
0 0.005 0.01 0.015 0.02 0.025 0.03
strains, -
stre
ss, M
Pa
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Digital Volume Correlation of WPCs
Just getting started
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XRT 3D volumetric reconstruction of gold-modified 40% wood/HDPE composite
2 mm
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Gold and holes
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Gold and holes
Work in progress…
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AcknowledgementAcknowledgement
This research is funded by the OSU General Research Fund Award, Fall 2004.