Online detection method for transient waves applied to continuous health monitoring of carbon-fiber-reinforced polymer composites with embedded optical fibers

Abstract

It has been proven that the embedment of optical fibers into a composite material could offer an alternative to robust piezoelectric transducers used for Acoustic Emission (AE) monitoring. In this configuration optical fibers are used as intensity-modulated sensors. A set of propagating elastic waves is generated whenever damage occurs in the composite material. These waves locally modify the optical and geometrical properties of the optical fiber and hence can be detected by them as a transient signal that modulates the light intensity. In this paper a method for detecting the transients by on-line signal processing is presented. It is then applied to optical signals resulting from tensile tests performed on CFRP composites material with embedded optical fibers. By means of the Short-Time Fourier Transform (STFT), the level of the noise added to the signal is estimated by filtering the time trajectories. This filter is continuously adapted according to the principle of minimization of the mean squared error. Finally the detection is achieved by a constant false alarm rate powerlaw detector. This technique is fast and doesn't take into account neither the statistical distribution of the noise nor the frequency content of the transients as long as the frequency component distribution can be approximated by an exponential law. The detected transient features can be correlated with the AE results but an off-line analysis and classification is still needed.

Acoustic emission monitoring using a polarimetric Single Mode optical fibre sensor

“…In order to detect these changes a segmentation of the discrete time signal and processing in the frequency domain are carried out. There are numerous motivations (Papy et al, 2003) for this choice:…”

“…Consequently, the detection of transient signals cannot be achieved by only applying a simple thresholding method to the raw signal whether it is in the time or in the frequency domain. Previously, a very fast and efficient detection technique (Papy et al, 2003) has been applied to multimode sensors. Since in the present case the output signal is of the same nature, this technique achieves comparable performances when it is applied to signals issued/stemmed from the polarimetric SM setup.…”

“…Based on the computation of the STFT and Wang's power-law criterion (Wang and Willett, 2001), an efficient extended power-law detector (Papy et al, 2003) has been derived:…”

A novel technique for acoustic emission monitoring in civil structures with global fiber optic sensors

“…The noise filter is continuously and automatically adapted throughout the test as the noise level might vary. Final detection of transients, which are identified as short-duration non-stationarities, is achieved by a constant false alarm rate power-law detector [35,36]. A more detailed description of this algorithm can be found in Papy et al [35].…”

“…Final detection of transients, which are identified as short-duration non-stationarities, is achieved by a constant false alarm rate power-law detector [35,36]. A more detailed description of this algorithm can be found in Papy et al [35]. Data acquisition and processing is performed in real-time using LabVIEW software.…”