10-2 Wang Updated Tappi 2007 Nano_060707 Jk

8/11/2019 10-2 Wang Updated Tappi 2007 Nano_060707 Jk

1/22

2007 International Conference on

Nanotechnology for the Forest Products Industry

Knoxville Convention Center, June 13-15, 2007

Siqun Wang, Seung-Hwan Lee, Cheng Xing,

George M. Pharr

University of Tennessee

Nano-Mechanical Properties of Cellulose Fibers

by Nanoindentation


2/22


3/22

IntroductionsSiqun Wang

To design fiber reinforced polymer composites, we

need to know

Matrix

Fiber

Interphase


4/22

Research Goals and Materials

Objectives:

To investigate nano mechanical properties of cellulose fibers by nanoindentation;

To compare data between nanoindentation and conventional tensile test;

To understand what could happen if fiber diameter is too small or fiber cell wall is too

narrow.

Siqun Wang

Materials:Two types of Lyocell fiber

Refined wood fibers under different

refining steam pressure

The image of refining fiber a) juvenile wood at 2 MPa, b) mature wood

at 2 MPa, c) juvenile wood at 18 MPa, and d) mature at 18 MPa.


5/22

Research Goals and MaterialsSiqun Wang

Materials:

Refined wood fibers under different refining steam pressure

2 Bars 12 Bars 18 Bars


6/22

Experimental MethodSiqun Wang

Lyocell fiber:

Tensile test (Tensile modulus)Nanoindentation (hardness, elastic modulus,

creep)

X-ray diffraction (crystallinity)

AFM

Refined wood fibers under different refining

steam pressure:Nanoindentation (hardness, elastic modulus,

creep)

AFM

Nanoindentation influenced by neighboring

materials via finite element analysisSingle fiber nano-

mechanical testing system


7/22

Nanoindentation Instrument and Indentation

Procedure

Schematic of the NANO II

Indenter

Indent

marks

s

Le30

LfLf Le

h63.5

77

S = 2

Le/tan30

H = Lf + Le

S = 2h (tan65.3 )/(tan30 )

Lf = h (tan77 ) Le = h(tan65.3 )

H = h (tan77 + tan 65.3)

Geometry of nano-indenter

(Berkovich diamond tip)


8/22


Procedure

2

max

5.24ch

P

A

PH

Hardness (H):

Indentationforce,

P

Displacement, h

dP/dh

Loading

Unloading

hc

Typical load-displacement curve

Adh

dPE

r

2

1

1

2

2 111

i

i

r

ss

EE

E

Elastic modulus (Es):

(Oliver and Pharr)

Vs and Vi (0.07) are the Poissons ratios of

the specimen and indenter, respectively.

Eiis the modulus of theindenter (1141 GPa).

Eris reduced elastic modulus, which accounts

for the fact that elastic deformation occurs in

both the sample and the indenter.


9/22


Procedure

Load,

P

Displacement, h

With single experiment, cycles of

indentation, each of which consistsof incremental loading and partialunloading, are performed until afinal desired depth is attained.

Each loading-and-partial unloadingcycle provides a series of values ofhardness and elastic modulus.

Continuous stiffness measurement: One of the significantimprovements in nanoindentation test


10/22

ResultsLyocell fiberSiqun Wang

Tensile modulus of Lyocell fibers by single fiber tensile test and

sample codes for specimens

Sample Code Fiber direction Tensile modulus

(GPa)

Index of crystallinity

(%)

Lyo13 (L) Longitudinal 12.64 (2.94) 67.5

Lyo13 (T) Transverse - -

Lyo10 (L) Longitudinal 10.36 (1.88) 65.4

Lyo10 (T) Transverse - -

The value in parenthesis is the standard deviation (SD)


11/22


Hardness and elastic modulus of Lyocell fibers measured by

continuous nanoindentation

Sample Mean value from 150

to 300 nm depth (GPa)

Unloading value at final

indentation depth (GPa)

H mean E mean Hu Eu

Lyo13 (L) 0.44

(0.06)

13.19

(0.10)

0.43

(0.05)

13.10

(0.10)

Lyo13 (T) 0.32

(0.02)

6.77

(0.28)

0.33

(0.02)

6.69

(0.25)

Lyo10 (L) 0.33

(0.05)

11.51

(1.27)

0.32

(0.06)

11.42

(1.25)

Lyo10 (T) 0. 30

(0.01)

6.09

(0.14)

0. 30

(0.01)

6.01

(0.13)

Each is the average value from 5 indents. The value

in parenthesis is the standard deviation (SD).


12/22


Hardness and elastic modulus of Lyocell fibers measured by continuous

nanoindentation

Sample Mean value from

150 to 300 nm depth

(GPa)

Unloading value at final

indentation depth (GPa)

H mean E mean Hu Eu

Lyo13 (L) 0.44

(0.06)

13.19

(0.10)

0.43

(0.05)

13.10

(0.10)

Lyo13 (T) 0.32

(0.02)

6.77

(0.28)

0.33

(0.02)

6.69

(0.25)

Lyo10 (L) 0.33

(0.05)

11.51

(1.27)

0.32

(0.06)

11.42

(1.25)Lyo10 (T) 0. 30

(0.01)

6.09

(0.14)

0. 30

(0.01)

6.01

(0.13)

Each is the average value from 5 indents. The

value in parenthesis is the standard deviation

(SD).

Sample

Code

Fiber direction Tensile

modulus

(GPa)

Index of

crystallinity

(%)

Lyo13 L) Longitudinal 12.64

(2.94)

67.5

Lyo13 T) Transverse- -

Lyo10 L)

Longitudinal 10.36

(1.88)65.4

Lyo10 T) Transverse- -


13/22


Creep behaviors of Lyocell fibers

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300

Holding time (s)

Load(mN)aaa

200s

Hold segment

Loading

Experimental scheme for creep

test by nanoindentation.

-3.45

-3.35

-3.25

-3.15

-0.7 -0.6 -0.5

Log () (GPa)

Log

()(sec

-1

)

Lyo8 (T)

Lyo8 (L)

Lyo15 (T)

Lyo15 (L)

Lyo10 (T)

Lyo13 (T)

Lyo10 (L)

Lyo13 (L)

-3.45

-3.35

-3.25

-3.15

-0.7 -0.6 -0.5

Log () (GPa)

Log

()(sec

-1

)

Lyo8 (T)

Lyo8 (L)

Lyo15 (T)

Lyo15 (L)

Lyo10 (T)

Lyo13 (T)

Lyo10 (L)

Lyo13 (L)

The plot of indentation strain rate () and contact

stress (hardness, ) obtained from data

corresponding to the holding segment. Load:

1000 N, Loading rate: 20 N/s, Holding time200 s.


14/22

ResultsRefined wood fibersSiqun Wang

Summary of nanoindentation results of fiber cell wall

Note: Stdev: standard deviation; CV: coefficients of variation; Ci: indention creeps; n: the number of indents.

Property/pressure 2 bars 4 bars 6 bars 8 bars 10 bars 12 bars 14 bars 18 bars

Es

GPa

H

GPa

Ci

%

n

Mean

Stdev

CV

Mean

Stdev

CV

Mean

Stdev

CV

Number

21.35

2.59

12.13

0.50

0.04

8.00

7.58

0.86

11.35

31

18.62

2.97

15.95

0.47

0.062

13.19

8.72

1.56

17.89

27

15.96

2.41

15.10

0.47

0.07

14.89

8.87

1.25

14.09

23

16.83

2.53

15.03

0.45

0.05

11.11

8.63

1.29

14.95

28

15.32

2.51

16.38

0.43

0.067

15.58

8.24

1.09

13.23

30

14.05

2.87

20.43

0.43

0.079

18.37

9.68

1.79

18.49

28

13.09

3.42

26.13

0.39

0.078

20.00

12.30

3.89

29.25

14

12.22

3.29

26.92

0.37

0.095

25.68

13.08

3.91

29.89

13


15/22

ResultsFinite element analysisSiqun Wang

Poplar cell wall

Manchurian Ash

cell wall

Adhesive transitionzone from the fiber

to matrixMatrix

Fiber

Indents


16/22



17/22


Fiber

E=18.65Gpa,H= 0.69 Gpa

Epoxy

E =4.67 Gpa ,H =0.16 Gpa

Perform one simulationwhen the location of the

flat punch moves to the

left or the right with every

1um

Rigid Flat punch

radius =1um1um

8 simulations 8 simulations

Total 16 simulations


18/22


Boundary Conditions:

Penetration depth: 50nm applied to the indenter Axisymmetry BCs: applied to the center face.

Roller BC: applied to the bottom face.


19/22


Mesh Rigid flat cylindrical punch

Symmetry

plane

100um

1

00um

100um

Fiber

Matrix

100um

Rigid flat cylindrical punch

Symmetry

plane

100um

1

00um

100um

Fiber

Matrix

100um

100um

1

00um

100um

Fiber

Matrix

100um


Symmetry

plane

100um

1

00um

100um

Fiber

Matrix

100um


Symmetry

plane

100um

1

00um

100um

Fiber

Matrix

100um

100um

1

00um

100um

Fiber

Matrix

100um


20/22


0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8

Centerline location of flat cylinderical punch (um)

Stiffness

(mN/nm)

FEA

Sneddon's solution-Epoxy

Sneddon's solution-Fiber

Fiber

Epoxy

Variation of the stiffness measured from the FEA with position from the interface. The punchradius is 1 m.


21/22

SummarySiqun Wang

Nanoindentation with continuous stiffness measurement is well

suited to the evaluation nano-mechanical and time-dependentmechanical properties of cellulose fibers in longitudinal and

transverse direction. There is no significant difference between

modulus values obtained by nanoindentation and single fiber

tensile test.

There are some advantages using nanoindentation than tensile

test.

Using existing nanoindentation technique it would be difficult to

calculate the exact mechanical properties without the effect of

neighboring material property in at least 8 times smaller region

than indent size.


22/22

AcknowledgementsSiqun Wang

Haitao Xu, Yan Wu, Matthew Kant, Dayakar

Penumadu

USDA NRI grant number # 2005-02645

USDA Wood Utilization Research Grant

Tennessee Agricultural Experiment Station MS#96

Oak Ridge National Laboratory

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10-2 Wang Updated Tappi 2007 Nano_060707 Jk

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