The authors have demonstrated previously that reinforcing glass fibres can be used as light-guides to facilitate chemical
process monitoring and structural integrity assessment of fibre reinforced composites. In the current paper, the authors
explore concepts for the development of self-sensing, self-healing and crack-arrestor composites.
The first part of the papers presents a brief overview of previously reported technologies for self-sensing, self-healing
and crack-arrestor; the advantages and disadvantages of the various technologies are discussed. The second part of this
paper present the design concept and performance requirements for the self-sensing, self-healing and crack-arrestor
composites. The final part of the paper presents preliminary results on the manufacture and evaluation of this class of
Fibre Bragg grating (FBG) sensors continue to be used extensively for monitoring strain and temperature in and on
engineering materials and structures. Previous researchers have also developed analytical models to predict the loadtransfer
characteristics of FBG sensors as a function of applied strain. The general properties of the coating or adhesive
that is used to surface-bond the FBG sensor to the substrate has also been modelled using finite element analysis.
In this current paper, a technique was developed to surface-mount FBG sensors with a known volume and thickness of
adhesive. The substrates used were aluminium dog-bone tensile test specimens. The FBG sensors were tensile tested in
a series of ramp-hold sequences until failure. The reflected FBG spectra were recorded using a commercial instrument.
Finite element analysis was performed to model the response of the surface-mounted FBG sensors. In the first instance,
the effect of the mechanical properties of the adhesive and substrate were modelled. This was followed by modelling the
volume of adhesive used to bond the FBG sensor to the substrate. Finally, the predicted values obtained via finite
element modelling were correlated to the experimental results. In addition to the FBG sensors, the tensile test specimens
were instrumented with surface-mounted electrical resistance strain gauges.
The focus of this paper is on real-time damage detection in reinforcing fiber bundles and composites using high-speed
photography and image analysis. In other words, the end of a reinforcing fiber bundle or composite is imaged and the
sequence of fiber fracture is monitored using a high-speed camera. These studies were undertaken using as-received and
silane-treated custom-made optical fibers of around 12 μm diameter and E-glass fibers of 15 (±3) μm diameter.
The first part of this paper reports on the techniques that were developed to produce void-free test specimens and the
procedures used for imaging the end of the fiber bundle and composite during tensile loading. Evanescent wave
spectroscopy was used to study the effect of silane treatment on the cross-linking kinetics of an epoxy/amine resin
system. Conventional piezo-electric acoustic emission (AE) transducers were used to monitor the acoustic events
occurring during the tensile test. The signals from the AE transducers were used to trigger the high-speed camera.
The second part of this paper presents details of the image analysis routines that were developed to track the light
intensity transmitted through individual fibers during tensile loading. Good correlation was observed between the
transmitted light intensity and the AE signals.
Significant progress has been made in recent years on the design and deployment of optical fibre-based sensors to
monitor the cross-linking (cure) reactions in thermosetting resins. In the current study, the following sensor designs
were used to study cross-linking reactions of an epoxy/amine resin system: (i) intensity-based Fresnel sensors, (ii)
extrinsic fibre Fabry-Perot interferometic (EFPI) sensors, (iii) fibre Bragg grating (FBG) sensors and (iv) sensor designs
to enable transmission, reflection and evanescent wave spectroscopy.
This paper presents a detailed study on a comparison of the above-mentioned techniques for a commercially available
epoxy/amine resin system. Conventional Fourier transform infrared spectroscopy was used as the reference method for
obtaining quantitative data on the cross-linking kinetics. The shrinkage of the resin during cross-linking was monitored
using EFPI and FBG sensors. This paper also discusses the cross-linking data obtained using optical fibre-based
evanescent wave spectroscopy.
This paper presents the design, theory, characterisation and application of a novel fibre optic acoustic emission (AE)
sensor. The sensor consists of a pair of optical fibres that are heated, fused and drawn to create a fused-tapered region
that is sensitive to acoustic perturbations. The sensor is housed in a silica V-groove. The modelling of this fibre optic AE
sensor is presented with a finite element analysis on the strain field based on the effect of the geometry within the
sensing region. The characterisation of the sensor was carried out using a glass block with 160mm thickness as an
acoustic medium. The applications of this sensor were demonstrated in three experiments. Firstly, the sensor was
surface-mounted in carbon fibre reinforced composite samples and tested to failure under tensile loading. In the second
experiment, the sensor was surface-mounted on double-cantilever Mode-I test specimens. The AE response from the
sensor was correlated to the inferred modes of failure during the Mode-I test. In the third experiment, the sensor was
surface-mounted onto the composite "blow-off" test samples. The feasibility of using the sensor to detect damage
development in real-time was demonstrated.
The term self-sensing composites is used to describe the case where the reinforcing glass fibres in advanced fibre reinforced composites are used as the sensors for chemical process monitoring (cure monitoring). This paper presents conclusive evidence to demonstrate that reinforcing E-glass fibres can be used for in-situ cure monitoring. The cure behaviour of an epoxy/amine resin system was compared using evanescent wave spectroscopy via the reinforcing E-glass fibre and conventional Fourier transform infrared spectroscopy. This paper also reports for the first time that evanescent wave spectroscopy via E-glass fibres can be used to detect the presence of silane coupling agents. Preliminary results indicated that the cure kinetics on the E-glass fibre surface, as observed using evanescent wave spectroscopy, were influenced by the silane coupling agent.