JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 59

Fig. 6: a) Carbon fibre/epoxy/0.30wt% MWCNT composite Plate 4: a1) Plate 4 after six drilled holes of sizes 1/16, 2/16, 3/16, 4/16, 5/16 and 6/16 inches, a2) EPC distribution
after drilled holes, a3) effect of hole volume on EPC
b) Carbon fibre/epoxy/0.30wt% MWCNT composite Plate 5: b1) Plate 5 after impact damages 1 and 2 (each 78 J), b2) EPC distribution after impact damages
c) Carbon fibre/epoxy/0.30wt% MWCNT composite Plate 6: c1) schematic illustration of Plate 6 after impact damages 1, 2 and 3 (1 J, 2 J and 3 J), c2) EPC distribution of Plate 6

locations and values of the changes in electrical resistance due to the
drilled holes. By comparing Figures 5a1 and 5a2, it is clear that the
significant local variations in ERC distribution correspond exactly to
the locations of the holes drilled on Plate 1. Figure 5a3 presents the
effect of hole volume on ERC, demonstrating the effectiveness of the
technique to quantify the extent of damage. A high-velocity projectile
impact test was performed on Plate 2, as shown in Figure 5b1. Two
impact damages (1 and 2), each created at a 78-J energy level, were
detected and located based on the significant local variations in ERC
distribution (see Figure 5b2). Plate 3 was subjected to low-velocity
impacts with different energy levels ranging from 1 J to 3 J (see Figure
5c1). These energy levels were applied to create barely visible impact
damage (BVID) that cannot be detected by visual observations. These
BVI damages were detected and located according to the sharp local
variations in ERC distribution, as shown in Figure 5c2.
Conductive fibre/epoxy/MWCNT composite plates
Three carbon fibre/epoxy/0.30wt% MWCNT composite plates
(22×13 in., 560x330 mm2), numbered 4, 5 and 6, were considered.
Holes of sizes 1/16, 2/16, 3/16, 4/16, 5/16 and 6/16 inches, respectively, were drilled on Plate 4, as shown in Figure 6a1. Figure 6a2 shows
the locations and values of the change in electric potential due to the
drilled holes. Comparing Figures 6a1 and 6a2, a good correspondence
is observed between the sharp local variations in the EPC distribution
and locations of holes of different sizes drilled on Plate 4. Figure 6a3
shows the effect of hole volume on the EPC, revealing the capability of
the technique to determine the severity of the damages. High-velocity
projectiles (78 J each) were impacted on Plate 5 using a gas gun, as
shown in Figure 6b1. Impact damages 1 and 2 were detected and located distinctly according to the sharp local variations in EPC distribution
(see Figures 6b2). Plate 6 was tested under a low-velocity impact performed using drop weights with different energy levels ranging from 1 J
to 3 J. Plate 6 impacted at three different locations with different energy
levels is schematically illustrated in Figure 6c1. Figure 6c2 shows the
locations and values of absolute changes in electric potential for Plate 6
due to low velocity impact tests. Comparing Figures 6c1 and 6c2, it is
observed that there is a good correspondence between the significant
local variations in absolute EPC distribution and BVID zones. This

reveals that BVI damages 1, 2 and 3 produced by different energy levels
at different locations in Plate 6 are detected and located distinctly.

Conclusions
A new and practical SHM technique was developed for real-time
detection, location and quantification of damages in large composite
structures. This technique is based on real-time monitoring of electrical
property distribution over the surface of large intelligent composite
structures to sense sharp variations in electrical property change distribution as an indication for the detection, location and quantification of
damages. As such, the technique makes the large polymer composite
structures self-sensing, meaning that an operator can place the probes
anywhere in the structure to monitor health while the structure is in
operation. n
More information:
al_nag@encs.concordia.ca
hoasuon@alcor.concordia.ca
References
[1] Balageas D, Fritzen CP and Guemes A: Structural health
monitoring, ISTE, 2006.
[2] Li C, Thostenson ET and Chou TW: Sensors and actuators based on
carbon nanotubes and their composites:
A review, J. Compos Sci Technol 68 1227-1249, 2008.
[3] Naghashpour A and Hoa SV: In-situ monitoring of through-thickness strain in composite laminates using carbon nanotube sensors, J.
Compos Sci Technol, 78, 41-47, 2013.
[4] Naghashpour A and Hoa SV: A technique for real-time detection,
location and quantification of damages in large polymer composite
structures made of electrically non- conductive fibers and carbon
nanotube networks, J. Nanotechnology, 24, 455502, 2013.
[5] Naghashpour A and Hoa SV: A technique for real-time detecting, locating, and quantifying damage in large polymer composite structures
made of carbon fibers and carbon nanotube networks, J. structural
health monitoring, 14 (1), 35-45, 2015.
[6] Hoa SV and Naghashpour A: Method and system for detecting
and locating damages in composite structures, International Patent
Publication Number: WO2013086626A1.

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jec composites magazine 59

JEC COMPOSITES MAGAZINE - Issue #96 - April 2015

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