Monitoring mode II fracture behaviour of composite laminates
using embedded ﬁber-optic sensors
, Kin-Tak Lau
, Zhongqing Su
, Eric Tsun-Tat Wong
Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong, China
Laboratory of Smart Materials and Structures (LSMS), Centre for Advanced Materials Technology (CAMT), School of Aerospace,
Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia
Received 22 January 2006; accepted 7 July 2006
Available online 16 November 2006
Utilization of embedded Fiber Bragg Grating (FBG) sensors for monitoring mode II fracture behaviour of composite laminate beams
containing diﬀerent delaminations along the thickness-wise direction, by virtue of End-Notch Flexure (ENF) tests, is presented. Non-
uniform strain distribution due to the stress concentration at the delamination tip was examined by the way of observing the reﬂection
spectrum from the FBG sensor. The stress concentration in ENF specimens, which are subjected to various applied loads, was analyzed
in terms of the shift, shape, bandwidth and intensity of the reﬂection spectrum. Relationships between the load–displacement graphs and
the corresponding reﬂection spectra under ENF tests were established. In addition, the feasibility and reliability of using the embedded
FBG sensors for mode II fracture behaviour monitoring in the composite laminates is discussed.
Ó 2006 Published by Elsevier Ltd.
Keywords: A. Glass ﬁbres; A. Laminates; B. Delamination; D. Non-destructive testing
In the past decade, utilization of advanced composite
materials has emerged increasingly in a variety of engineer-
ing applications due to their superior and unique proper-
ties, such as relatively high strength-to-weight ratio and
excellence resistance in corrosion. However, advanced
composite structures are susceptible to delamination, one
of the predominant forms of ﬂaws in laminated composites
caused by a low velocity impact or a manufacturing defect.
Since delamination can play a major role in signiﬁcantly
lowering structural compressive strength, in-depth investi-
gation on the fracture behaviour of delaminated structures
is essential to eﬀectively maintain the structural integrity.
Motivated by this, much eﬀort has been paid to a real-
time structural health monitoring (SHM) recently [1–5].
Smart composite structures, which involve an integration
of adaptive sensors and actuators, have been rapidly devel-
oped in this area to cater for the requirement of the SHM.
Particularly, ﬁber Bragg grating (FBG), emerged recently
in this ﬁeld, is considered as an intrinsic smart sensor owing
to their lightweight, small size, immunity to electromag-
netic inference, good performance under the harsh environ-
mental conditions and capability for multiplexing.
Exploitation of embedded FBG sensors for monitoring
the delamination in the advanced composite structures
has been widely investigated [6–9]. Leng and Asundi 
employed a FBG sensor to inspect delamination in com-
posite laminates under a three-point bending test, to con-
clude that the ﬂexural strain of damaged structures was
relatively higher than that of those undamaged structures
under static loads. Ling et. al.  quantitatively determined
delamination size and location of composite beams by
using FBG sensors associated with a genetic algorithm.
And Takeda et. al. demonstrated that small-diameter
FBG sensors are eﬀective in evaluating delamination in
1359-8368/$ - see front matter Ó 2006 Published by Elsevier Ltd.
E-mail address: firstname.lastname@example.org (H.-Y. Ling).
Composites: Part B 38 (2007) 488–497