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5/5/2013
1
“Self-sensing of damage in carbonnanotube/vinyl ester composites”
Francis Avilés (speaker)*José de Jesús Kú-Herrera
Alejandro May Pat
Materials Department, Scientific Research Center of Yucatan (CICY) , Mérida, Yucatán, Mexico.
6th International Conference on Composite Testing and Model Identification, Aalborg, Denmark, April 22-24 2013.
*On Sabbatical leave at :Aalborg University, Department of Mechanical and Manufacturing Engineering.Email: faviles@cicy.mx
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Outline
• Motivation
• Research Overview
• Materials and methods
• Results
• Conclusions
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MotivationThe addition of small amounts of carbon nanotubes (CNTs) into a polymermatrix can form a conductive percolating network which changes its electricalresistance when is deformed (piezoresistivity). This electrical signal could alsobe used to monitor damage in polymer composites.
Structural health monitoring
P
R L
P
L
3
Coupled electro-mechanical measurements
R/R0
NanocompositeManufacturing(MWCNT/VER)
Correlation between mechanical (-) response
and electrical resistance (R)
Tension and compression testing (quasi-static and low
cycles)
Research Overview
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Materials and
Methods
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MWCNT Bayer C150PL = 1-4 m, di ≈ 4 nm, do ≈ 13 nm
Epoxy vinyl ester DerakaneMomentum 470-300
Solution casting
[1] Cyclic tension and compression piezoresistivity of carbon nanotube/vinyl ester composites in the elastic and plastic regimes, J.J. Ku-Herrera, F. Avilés, Carbon, Vol. 50(7), 2012, 2592-2598.
Materials and composite preparation [1]
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Electrical and piezoresistive characterization
Strain Indicator
Multimeter
Grips
Specimen
R25.4 mm
8 mm R
Electrical conductivity
Tension Compression
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Results
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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Log 10
e (
e in S
/m)
MWCNTs (% w/w)
Electrical conductivity
Φc ≈ 0.20 wt%
9Electrical percolation obtained between slightly below 0.2 wt. %
MWCNT/VER composites
0 5 10 15 20 25 30 35 400.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
R/
R0 (
%)
(MPa)
0.00 0.25 0.50 0.75 1.00 1.25 1.500.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
R/R
0 (%)
(%)
0R RK
Tensile piezoresistivity:Quasi-static loading 0.3 wt% MWCNT/VER
R/R0 vs
R/R0 vs MWCNT wt % Gauge factor
0.3 2.60 ± 0.13
0.5 2.44 ± 0.13
1.0 2.31 ± 0.17
0.00 0.25 0.50 0.75 1.00 1.25 1.500
5
10
15
20
25
30
35
40
45
(M
Pa)
(%)
vs
10
Linear piezoresistivity observed at all strain levels before fracture (brittle
polymer composite).
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Tensile piezoresistivity: Cycling loading0.3 wt% MWCNT/VER
0 100 200 300 400 500 600 7000
2
4
6
8
10
M
Pa)
Time (s)
0.00 0.05 0.10 0.15 0.20 0.25 0.300
2
4
6
8
10
(M
Pa)
(%)
0 100 200 300 400 500 600 7000.0
0.1
0.2
0.3
0.4
0.5
R/R
0(%)
Time (s)
0 100 200 300 400 500 600 7000.00
0.05
0.10
0.15
0.20
0.25
0.30
(%
)
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0 2 4 6 8 10 12 14 16 18 20 22 24
0
20
40
60
80
100
120
140
160d
c c'
(%)
(M
Pa)
a
b
o 0
20
40
60
80
100
120
140
160
R
/R0 (
%)
dc'
c
R/R0
a bo
o o-a a-b b-d c-c’
Elastic Yielding Plastic
P
P
Compressive piezoresistivity
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Compressive piezoresistivity
0 2 4 6 8 10 12 14 16 18 20
-10
0
10
20
30
40
50
60
70
R
/R0 (
%)
(%)
0/R RK
PK EK
o a b
Linear approximation in two zones: ≈ 0-1% and 5-20%13
Compressive gauge factors
MWCNT wt % KE KP
0.3 0.91 ± 0.01 -9.37 ± 1.14
0.5 2.39 ±0.22 -8.40 ± 0.77
1.0 4.55 ±0.35 -3.99 ± 0.24
KEMWCNT(wt%)
KPMWCNT(wt%)
Elastic zone Plastic zone
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(Contact R) (Tunneling)
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Sensing of matrix cracking
15Changes in electrical resistance are sensitive to polymer (matrix) micro-cracking.
Micro-cracking
Compression: Cycling loading
0 50 100 150 200 250 300 350 400 450-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1 R/R0
t (s)
(%
)
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
R/R
0 (%
)
0 100 200 300 400 500 600 700 800 900-1.75
-1.50
-1.25
-1.00
-0.75
-0.50
-0.25
0.00
0.25 R/R0
t (s)
(%
)
-2.4
-2.0
-1.6
-1.2
-0.8
-0.4
0.0
0.4
R
/R0 (
%)
0 1000 2000 3000 4000-10-8-6-4-202468
10 R/R0
t (s)
(%
)
-20
-15
-10
-5
0
5
10
15
20
R
/R0(%
)
=0.5%
(a)
=1.5%
(b) =10%
0 2 4 6 8 10 12 14 16 18 20
0
20
40
60
80
100
120
140
160
vs
(%)
(M
Pa)
0
20
40
60
80
100
120
140
160
R/
R0
(%)
(a)
(b)
(c)
(c)
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Incremental compression loading0.3 wt% MWCNT/VER
Stress-strainCycling incremental strain
Incremental and permanent R
0 5 10 15 20 250
20
40
60
80
100
120
140
160
180
(M
Pa)
(%)
0.5 1.0 1.5 2.0 4.0 7.0 10 15 20
max(%)
0 5 10 15 20 25
0
50
100
150
200
(%)
max(%) 0.5 1.0 1.5 2.0 4.0 7.0 10 15 20
R/R
0 (%
)
Permanent changes in R can be correlated to irreversible phenomena occurringin the polymer (yielding and damage).
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Accumulated damage (compression)
PA= Accumulatedplastic strain.
For <2: For >2:
PA=0 RP=0 PA>0 RP>0
0 2 4 6 8 10 12 14 16
0
20
40
60
80
100
120
140
160
180
47 10
15
R
P/R0 (%
)
PA(%)
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Rp= Permanent R.
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Conclusions
• Electrical conductivity in MWCNT/VER composites can be achieved for MWCNT weight concentrations as low as 0.2 wt %.
• The piezoresistive behavior of MWCNT polymer composites depend strongly on the loading type and matrix mechanical behavior.
• The tensile piezoresistive behavior of (brittle) MWCNT/VER composites has a linear correlation with the nanocomposite’sdeformation under monotonic and cycling loading.
• The changes in electrical resistance (reversible and irreversible) areable to identify the elastic, yielding and plastic zones of thenanocomposite (compression loading).
• It is possible to correlate the irreversible (permanent) changes ofelectrical resistance to the generation and accumulation of damagein the composite.
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Thank you!
Questions?
20
Jesús Kú
Chichen Itza Mayan Castle,Yucatan, Mexico
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