Damages in composites, such as matrix cracks, delamination and fiber breakage, may occur as a result of excessive load, fatigue and low-velocity impact, etc. In the early stage of damage, mainly the matrix failures such as matrix cracking and delamination occur since the properties of matrix are weaker than that of reinforcement. In this study, fiber optic interferometers were applied in order to detect and evaluate the matrix failures of composites. Signal processing and calibration of fiber optic sensors were conducted. To overcome the 2π ambiguity of fiber optic interferometer, AEFPI (Absolute measurement Extrinsic Fabry-Perot Interferometer) and PS-EFPI (Phase-Shifted Extrinsic Fabry-Perot Interferometer) were developed to distinguish the direction of loading such as increase and decrease. Robust signal processing methods were proposed to real-timely monitor strain response of the structure with the negligible influence of environmental noise. To estimate the overall performance of composites, it is necessary to identify the influence of the buckling and delamination failure. For that reason, EFPI was applied to the delaminated composite beams to detect the onset of buckling and delamination growth. The delaminated composite beams subjected to the compressive load were tested to identify the signal characteristics of the fiber optic interferometric sensor. The signals of the fiber optic sensor due to damages such as buckling or delamination growth were quantitatively evaluated by short time Fourier transform and wavelet transform. This EFPI sensor with presented signal processing technique would be powerful to evaluate the damages of the structure.
