relationships between structure and selected phil ti … · relationships between structure and...

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

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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


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)

16.6..2009 Peter Niemz (Institute for Building Materials, Wood Physics; [email protected])

Hierarchical structure of softwood (Harrington, University of Canterbury, New Zealand)

4

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)


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 )


Niemz and Sonderegger (2003), based on Sell (1989)

6

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)


Niemz and Sonderegger 2003

7

Macroscopic structure-property relationships within a wood species

cf. dissertations of Wimmer (1991) und Burgert (2000)


Correlation between density and MOE for spruce

n = 981 specimens

Sonderegger et al. (2008)


Correlation between density and swelling for spruce

n = 981 specimens

/%)

ellin

g (%

/Sw

e

Sonderegger et al. (2008)


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


Sonderegger et al. (2008)g ( )

11

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


Jahrringlage in GradRing angle

12

Influence of wood rays on the radial tensile strength%

)ce

ntag

e(%

Ray

per

c

Burgert (2000)

Radial tensile strength (N/mm2)


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)


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)


Distribution of fibre lengths in a Douglas fir

J d Middl t

optimum around 40%

Jozsa and Middleton (1994; Forintek)


Microfibril angle distribution (Pinus radiata)


Jozsa and Middleton (1994; Forintek)17

Influence of microfibril angle on MOE, G, and shrinkage

Perpend.

Longit.

Astley, Harrington and others (1997)


y g ( )

18

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


Elastic engineering parameters for yew and spruce

Keunecke et al. (2008)


eu ec e et a ( 008)

20

Deformation bodies of yew and spruce, calculated on basis on experimental results

yew spruce

Keunecke et al (2008)Keunecke et al. (2008)


Radial density profiles (determined with SilviScan)

Yew Spruce

Keunecke et al. (2009)( )


Radial position [mm]. Zero = close to the pith Radial position [mm]. Zero = close to the pith

22

Radial microfibril angle profiles (determined with SilviScan)

Yew Spruce

Keunecke et al. (2009)( )


Radial position [mm]. Zero = close to the pith Radial position [mm]. Zero = close to the pith

23

Mechanical properties of single fibres


Keunecke et al. (2008)

24

3.2 Chemical structure

Extractives - sorption behaviour

Chemical structure - mechanical propertiesChemical structure mechanical properties


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)


Thumm (2002)

26

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


Hofmann et al. (2008)

27

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


FE-Modelling of moisture transfer through a solid wood panel (diffusion)

Gereke, ETH Zurich (2009)

glue line

glue line


20oC/65% 20oC/100%29

FE-simulation of waper vapor diffusion in glued wood(2 -adhesive layers), different diffusion coefficient


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)


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


Strain distribution during shringage of a 2-layer solid wood panel

surface

middle layer

surface


Paul Scherrer Institute (PSI), Villigen/Switzerland

Neutron radiation source: SINQsource: SINQ

SynchrotronRadiation

S isource: SwissLight Source(SLS)


( )

34

Diffusion test


Tested and calculated moisture distribution in spruce during diffusion (0%-27°C/87%RH)

Calculation:Second Fickian law


Structure of beech wood, reconstructed from scans with Synchrotron light

Resolution: 1 m, Sample diameter: 1 mm


Sample diameter: 1 mm

37

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)


Thanks for your attention!

ETH, Campus ZürichETH, Campus Zürich--HönggerbergHönggerbergIfBIfB, Wood , Wood PhysicsPhysics


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