A state-of-the-art review is presented regarding the research and development of in situ fibre optic damage detection and assessment systems (FODDAS) embedded in fibre-reinforced composite structures. Representative individual fibre optic strain sensors and distributed sensor networks are briefly described. A major emphasis is placed on their capabilities for detecting damage, determining damage location and assessing the nature of damage, arising primarily from specific events such as impacts or quasi-static stress overloads. The main features of such systems as custom-built and structure-specific units with minimal human involvement are highlighted. Issues that could affect the validity of the performance of such strain sensors are discussed. Fracture and non-fracture of fibre optic sensors are identified as two fundamentally different approaches for damage detection and their primary features are discussed in relation to location determination and evaluation of the nature of damage. The major advantages and limitations of each approach are discussed. Directions and areas of potential future research in the development of related FODDAS are highlighted.

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This paper reports on research work which is a comprehensive study involving the design of an extrinsic Fabry–Perot interferometric strain sensor (EFPI-SS), the manufacture of smart carbon/epoxy beams preconditioned with artificial delamination, and the testing of these beams in three-point bending. A loading applied to the beams was quasi-static in nature and this was selected in order to facilitate the accurate and reliable control of the beam deformations. The EFPI-SSs were validated for their sensing capacity and survivability via surface mounting and interior embedment. Artificial delaminations of two different sizes were embedded within the host beams to simulate damage. Their effect on the bending stiffness induced by quasi-static loading was examined using the embedded EFPI-SSs along with surface-mounted conventional strain gauges (SGs) on a comparative basis. A linear response was obtained from the EFPI-SSs up to a strain level of 0.5%, and this was in good agreement with interpolated strains as well as those from analytical prediction. It was shown that the embedded EFPI-SSs were able to differentiate the effect of the tensile delaminations on the bending stiffness when the level of strain was substantial. It was noted that the interior strain data from the EFPI-SSs in conjunction with the surface SG data were very useful for extrapolating the strain difference on both sides of the delaminations, so that the possibility of delamination propagation could be deduced.

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