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“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(%)

20

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?

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Jesús Kú

Chichen Itza Mayan Castle,Yucatan, Mexico