Processing of transient signals from damage in CFRP composite materials monitored with embedded intensity-modulated fiber optic sensors

In this research study, intensity-modulated fiber optic sensors, whose working principle is based on the microbending concept, are used to monitor the damage in C/epoxy laminates during tensile loading. The use of advanced signal processing techniques based on time–frequency analysis is explained in order to get information on the damage developing in the composite. The signal Short Time Fourier Transform (STFT) has been computed and several robust noise reduction algorithms have been applied. Principally, Wiener adaptive filtering, improved spectral subtraction filtering, minimum-phase FIR (Finite Impulse Response) filtering and Singular Value Decomposition (SVD)-based filtering have been used. An energy and frequency-based detection criterion is introduced to detect transient signals that can be correlated with the Modal Acoustic Emission (MAE) results and thus damage in the composite material. Hints are that time–frequency analysis and Hankel Total Least Square (HTLS) method can also be used for damage characterisation (delamination, matrix cracking and fiber breaking).