JEC COMPOSITES MAGAZINE - Issue #96 - April 2015 - 56

health monitoring

Health monitoring technique for
large composite structures
The present work focuses on a structural
health monitoring (SHM) technique to detect,
locate and quantify damages that occur in large
structures made of polymer-matrix composite
materials while the structures are subjected
to loading (Figure 1). In this technique, carbon
nanotubes (CNT) are added to the polymer. Long
fibres are then incorporated with the modified polymer to create an intelligent composite structure. The incorporation of nanotubes
makes the polymer electrically conductive.
The large structure is marked with grid points
where electrically-conductive materials (such as
silver for example) are deposited. The electrical
properties between the grid points are measured; these values are used as a reference set.
Upon the application of a sufficiently high load,
damage may occur at one or several locations
in the large structure. lt is demonstrated that
the occurrence of damage changes the electrical properties between the contact points surrounding the damage. The sharp change in the
electrical properties between contact points is
used as an indication for the detection, location
and quantification of damage in large composite
structures.

olymer-matrix composites are increasingly used in many
important engineering structures such as aircraft due to their
light weight, high strength, high stiffness and good fatigue
resistance. However, along with their advantages, they present many
issues. One of them is the ability to detect failure in composite structures, particularly for in-situ processes (i.e. detection and location of
damage during service). Many non-destructive evaluation (NDE)
techniques have been proposed to address this problem [1]. However,
their usefulness is limited due to their poor spatial resolution and
low in-situ capabilities. Next-generation aerospace structures require
incorporating multiple functionalities into the structures. This can be
achieved by coupling composite technology with nanotechnology.

A new solution based on CNTs
Among different types of nanoparticles, CNTs have been used as a
multifunctional additive because of their small size and exceptional
physical properties [2]. Incorporating CNTs at low concentration
into an epoxy resin as nanoscale conductors will create electrically conductive networks distributed around the structural fibres,
which also act as in-situ piezoresistive sensors. Upon application
of a mechanical load, the CNT network formed inside the epoxy
is deformed and, if the load is high enough to create cracks in the
matrix, the configuration of the CNT network is affected and
induces a change in the electrical properties. This approach is used
to overcome sensing challenges in NDE and, potentially, SHM
(Figure 1). Recently, many researchers added CNTs to epoxy-based
composites for detecting damage in small coupon samples [2, 3].
Real engineering structures are large and much bigger than the lab
size samples presented in most works. Scaling up the technique from

By
Dr. Ali Naghashpour
Postdoctoral Fellow
Dr. Suong Van Hoa
Professor
Concordia University

56 jec composites magazine / No96 April 2015

Fig. 1: Schematic illustration of the SHM technique developed

JEC COMPOSITES MAGAZINE - Issue #96 - April 2015

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