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MOTIVATION SPLIT HOPKINSON PRESSURE BAR RESISTANCE-BASED DAMAGE SENSING

Resistance-Based Sensing in Carbon Nanotube Composites Under Dynamic Loads

A. S. Wu, Q. An (PhDMSEG), T-W. Chou and E. T. Thostenson

University of Delaware . Center for Composite Materials . Department of Mechanical Engineering

t Failure prediction in advanced materials is critical to their success in high-performance applications. •  In FRPs, the onset of failure due to matrix cracking and

interphase debonding often occurs without a significant decrease in load-carrying capability.

t Nondestructive damage sensing approaches: •  off-line (e.g., ultrasonic C-scanning, X-ray microtomography

and liquid penetrant)

•  real-time (e.g., time-domain reflectometry, acoustic emission and electrical resistance measurements)

t Resistance-based sensing allows for both off-line and real-time health monitoring.

Conductively modified carbon nanotube-based composites and their electrical response to dynamic loading is the focus of this research.

CURRENT RESEARCH CONCLUSIONS

ACKNOWLEDGEMENTS U.S. Army Research Office

Grant No. W911NF-09-1-0114 Dr. Bruce LaMattina

U.S. Office of Naval Research Grant No. N00014-09-1-0365

Dr. Yapa Rajapakse

Specimen (SP)

LSB

LIB LTB

LSG-1 LSG-2

HS

Incident Bar (IB)

Transmission Bar (TB)

Striker Bar (SB)Strain Gage (SG-1) Strain Gage (SG-2)

t Consists of a striker bar (SB), incident bar (IB) and transmission bar (TB)

t A gas gun propels the striker bar, which impacts the incident bar. •  This results in a stress wave to propagate through the

incident bar (σI) to the bar-specimen interface. •  The degree of acoustic impedance mismatch and the

specimen geometry control the amount of stress reflected back through the incident bar (σR) and transmitted through the transmission bar (σT).

t Measures the mechanical response of a specimen to dynamic compression loading.

t Preform: twenty plies of plain woven E-glass fabric •  Fabric is treated with a carbon nanotube-based sizing agent

then infused with SC-15 epoxy resin.

t Carbon nanotubes are deposited at the fiber surface resulting in electrical percolation in a composite specimen. •  The resistance of this nanotube

network is particularly sensitive to interphase debonding and delamination.

t Panel is cut to yield 45º off-axis specimens

0.00 0.02 0.04 0.06 0.08 0.10 0.120

20

40

60

80

100

120

140

160

(7)

(6)

(5)(4)(3)

(2)

σ    (MPa)

ε

εmax

 (s -­‐1)

(1)  618(2)  572(3)  851(4)  1000(5)  1260(6)  1130(7)  1202

.

(1)

RESULTS

11 12 13 14 150

5

10

15

20

25

30

7

6

53,4

 

 

ΔR    (kΩ

)

VE    (m/s )

1,2

t  Single specimen impacted multiple times at increasing energy •  Stiffness decreases after each impact. •  Anomaly in stress response due to large

delamination during impact (6)

t  Permanent resistance changes after each loading indicates damage.

t  Record resistance on the experimental timescale (~300 µs) •  Stress and resistance are plotted vs. time below:

t  Resistance increases during compression due to radial electrode configuration •  Specimens undergo axial compression and radial

tension (Poisson’s effect).

100 200 300 4000

10

20

30

 

σ    (MPa)

t    (µs )

 σ

loading

unloading

4

5

6

7

8

9

10

11

 R

 R    (k

Ω)

t  Achieved electrical percolation in a thick section composite using a carbon nanotube-based fiber sizing agent.

t  Demonstrated effectiveness of the carbon nanotube network in sensing damage during dynamic compressive loading.

Lim, An, Chou and Thostenson (2010) Mechanical and electrical response of carbon nanotube-based fabric composites to Hopkinson bar loading. Composites Science and Technology 71:616-621

DAMAGE BEHAVIOR t  Delamination occurs in these 45º off-axis

specimens. t  Future work includes:

•  Exploring electrode configurations which are more sensitive to this mode of failure and

•  Measuring the resistance response to dynamic compression-induced shear failure