Relationships between structure and selected h i l ti f dphysical properties of wood
Peter Niemz, Daniel Keunecke, Walter Sonderegger
ETH Zürich - Institute for Building Materials (Wood Physics)
[email protected]; www.ifb.ethz.ch/wood
1. Introduction
Wood
• Complex polymer p p y(see Ashby 2006)
• Orthotropic and anisotropic materialmaterial
• Influence from grain angle and ring angle
16.6..2009 Peter Niemz (Institute for Building Materials, Wood Physics; [email protected]) 2
Three-dimensional Hooke’s Law
1
3
31
2
21
1
0001EEE
1• 3 Young’s and 3 shear moduli
• 6 Poisson’s ratios
3
2
2313
3
32
21
12
321
0001
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3
2
• 6 Poisson s ratios
• Influence of grain angle and growth ring angle
23
3
23
321
001000
000
G
EEE
23
3
g o t g a g e
• Mechano-sorptive effect
• Visco-elastic and plastic
12
13
13100000
010000
G
G
12
13
Visco-elastic and plastic properties
12G
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2. Structural levels of wood
Tree (0.1-1 m)• Tree (biomechanics)
• Macroscopic levelp(growth rings, grain direction, knots)
Board (10-100 mm)Growth ring (0.5-15 mm)Cell wall
• Microscopic level(earlywood, latewood, porosity)
Tracheid (20-40 μm)(1-5 µm) • Sub-microscopic level
(cell wall, microfibril angle)
Molecules (<1 nm) • Chemical structure(cellulose, lignin, extractives, crystallinity)Microfibrils (3-10 nm)
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Hierarchical structure of softwood (Harrington, University of Canterbury, New Zealand)
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3. Examples for structure-property relationshipsrelationships
3.1 Structural elements, mechanical-physical properties3.1 Structural elements, mechanical physical properties
compiled for 103 different wood species based on
Sell (1989)
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Correlation between density and bending strength
200
250
y = 155.5x - 1.278R² = 0.792
150
(N/m
m2 )
100MO
R (
50
00 0.2 0.4 0.6 0.8 1 1.2 1.4
Density (g/cm3 )
16.6..2009 Peter Niemz (Institute for Building Materials, Wood Physics; [email protected])
Niemz and Sonderegger (2003), based on Sell (1989)
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Correlation between density and thermal conductivity
0.25
0.3
y = 0.161x + 0.043R² = 0.699
0.2
y(W
/mhK
)
0.1
0.15
cond
uctiv
it
0.05
Ther
mal
00 0.2 0.4 0.6 0.8 1 1.2 1.4
Density (g/cm3)
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Niemz and Sonderegger 2003
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Macroscopic structure-property relationships within a wood species
cf. dissertations of Wimmer (1991) und Burgert (2000)
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Correlation between density and MOE for spruce
n = 981 specimens
Sonderegger et al. (2008)
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Correlation between density and swelling for spruce
n = 981 specimens
/%)
ellin
g (%
/Sw
e
Sonderegger et al. (2008)
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Density (g/cm3)
Correlation between annual width and density for spruce
n = 981 specimens700
600
n kg
/m3
500
Dens
ity (
) in
553 66 29 23* R2 0 21
400
D
= 553.66 - 29.23*rw, R2 = 0.21
3000 1 2 3 4 5 6
Annual ring width (rw) in mm
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Sonderegger et al. (2008)g ( )
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Correlation between MOE and growth ring angle (RT) for spruce
1200
Astigkeit n=780 samples
T R knots
ETH Zurich (2009)1000
12
in
N
mm
2
00.30.2
T R
)
knots
ETH Zurich (2009)
800
10
odul
(qu
er)
in
(N/m
m2)
Theoretical calculation see Nairn (2007 Holzforschung)60
080
E−
Mod
MO
E
(2007, Holzforschung)
Influence on E- and G-moduli
60
0 30 45 60 90
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Jahrringlage in GradRing angle
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Influence of wood rays on the radial tensile strength%
)ce
ntag
e(%
Ray
per
c
Burgert (2000)
Radial tensile strength (N/mm2)
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Need for further research
Orthotropic elasticity (E,G, µ), interesting effects such as negative Poisson’s ratios (Grimsel 1999, Szalai 1994), time dependence (PhD f F d 2007)(PhD from Frandsen 2007)
Influence of moisture, temperature and time, p
Properties of many species still unknown (most insights, so far, for spruce wood)
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Structure-property relationships at the micro and sub-micro level
Distribution of fibre lengths in the stem
Microfibril angles (compression wood difference betweenMicrofibril angles (compression wood, difference between earlywood and latewood)
Influence of extractives content ( on the sorption behaviour onInfluence of extractives content ( on the sorption behaviour, on the MOE, on G, on the ultimate strain)
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Distribution of fibre lengths in a Douglas fir
J d Middl t
optimum around 40%
Jozsa and Middleton (1994; Forintek)
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Microfibril angle distribution (Pinus radiata)
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Jozsa and Middleton (1994; Forintek)17
Influence of microfibril angle on MOE, G, and shrinkage
Perpend.
Longit.
Astley, Harrington and others (1997)
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y g ( )
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Comparison between spruce and yew (Dissertation Keunecke, ETH 2008)
Yew
Higher density compared to spruce(yew 600-750 kg/m3, spruce 400-450 kg/m3)
Longitudinal MOE slightly lower for yew compared to spruce
Higher shear modulus for yew in especially in the RT plane Higher shear modulus for yew in especially in the RT plane
Causes for the special material behaviour of yew:
- Lower density difference between earlywood and latewood
- Higher microfibril angle for yew, espacially in the latewood
16.6..2009 Peter Niemz (Institute for Building Materials, Wood Physics; [email protected]) 19
Elastic engineering parameters for yew and spruce
Keunecke et al. (2008)
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eu ec e et a ( 008)
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Deformation bodies of yew and spruce, calculated on basis on experimental results
yew spruce
Keunecke et al (2008)Keunecke et al. (2008)
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Radial density profiles (determined with SilviScan)
Yew Spruce
Keunecke et al. (2009)( )
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Radial position [mm]. Zero = close to the pith Radial position [mm]. Zero = close to the pith
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Radial microfibril angle profiles (determined with SilviScan)
Yew Spruce
Keunecke et al. (2009)( )
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Radial position [mm]. Zero = close to the pith Radial position [mm]. Zero = close to the pith
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Mechanical properties of single fibres
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Keunecke et al. (2008)
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3.2 Chemical structure
Extractives - sorption behaviour
Chemical structure - mechanical propertiesChemical structure mechanical properties
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Correlation between chemical composition and mechanical properties
used to
• predict mechanical properties (MOE)
P di t th h i l• Predict the chemical composition (Cellulose, Lignin, …)
Thumm (2002)
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Thumm (2002)
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Linear correlations between chemical and physical/mechanical parameters (thermally modified hardwood)
Parameter 1 Parameter 2 RSoluble carbohydrates MOE -0.7330
SolubleSoluble carbohydrates Bending strength -0.6695
Phenol content Bending strength 0 5852Phenol content Bending strength -0.5852Phenol content Colour (L-value) -0.5272
Hofmann et al (2008)
Hemicelluloses Bending strength -0.0520
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Hofmann et al. (2008)
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4. FE modelling of structure-property relationshipsrelationships
Mechanical properties
K Persson L nd (2000) K. Persson, Lund (2000) M. Sedighi-Gilani, Lausanne (2006) E. Landis, Maine/USA and others
Heat and moisture transport
• Dissertation Frandsen, Denmark (2007): hygroelastic properties• Dissertation Harington, New Zealand (2002): hygroelastic propertiesg , ( ) yg p p• Svensson, Denmark (2008): hygroelastic properties• Dissertation Gereke, ETH Zürich (2009): warping of solid wood
Researchers with an educational background in mechanics physics civil Researchers with an educational background in mechanics, physics, civil engineering
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FE-Modelling of moisture transfer through a solid wood panel (diffusion)
Gereke, ETH Zurich (2009)
glue line
glue line
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20oC/65% 20oC/100%29
FE-simulation of waper vapor diffusion in glued wood(2 -adhesive layers), different diffusion coefficient
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5. New methods for structural analysis (selection of projects carried out at ETH(selection of projects carried out at ETH Zurich)
Big advances in wood physics over the last 20 years regarding testing methods
New methods for structural analysis (µCT Synchrotron neutrons)(µCT, Synchrotron, neutrons)
New methods for failure analysis (ESPI, VIC, multi channel AE)
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F
Strain distribution in spruce under compressionfor different ring angle), tested with
Vid I C l tiVideo Image Corelation
F F
ring angle 45° ring angle-Poisson,ratio
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Strain distribution during shringage of a 2-layer solid wood panel
surface
middle layer
surface
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Paul Scherrer Institute (PSI), Villigen/Switzerland
Neutron radiation source: SINQsource: SINQ
SynchrotronRadiation
S isource: SwissLight Source(SLS)
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( )
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Diffusion test
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Tested and calculated moisture distribution in spruce during diffusion (0%-27°C/87%RH)
Calculation:Second Fickian law
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Structure of beech wood, reconstructed from scans with Synchrotron light
Resolution: 1 m, Sample diameter: 1 mm
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Sample diameter: 1 mm
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Penetration of a 1C PUR prepolymer into beech (Synchrotron tomography)
Resolution:1 mResolution:1 m
Hass, Wittel, Niemz (ETH Zürich)Stampanoni (PSI/ETH)Stampanoni (PSI/ETH)
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Thanks for your attention!
ETH, Campus ZürichETH, Campus Zürich--HönggerbergHönggerbergIfBIfB, Wood , Wood PhysicsPhysics
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