Classification of composite damage from FBG load monitoring signals

Abstract

This paper describes a new method for the classification and identification of two major types of defects in composites, namely delamination and matrix cracks, by classification of the spectral features of fibre Bragg grating (FBG) signals. In aeronautical applications of composites, after a damage is detected, it is very useful to know the type of damage prior to determining the treatment method of the area or perhaps replacing the part. This was achieved by embedding FBG sensors inside a glass-fibre composite, and analysing the output signal from the sensors. The glass-fibre coupons were subjected to mode-I loading under tension-compression and static tests, in order to induce matrix cracks and delamination damages respectively. Afterwards, using wavelet features extracted from spectral measurements of the FBG sensors, classification of the damage type was carried out by means of support vector machines as a general classification tool with a quadratic kernel.

Calculation of the Mean Strain of Smooth Non-Uniform Strain Fields Using Conventional FBG Sensors

“…Coming back to the approximation (14), we see that the reflected spectrum can be approximated by a scaled (squared) sinc function having a possible offset. This approximation only holds in the wavelength range |λ − λ B | > λ th .…”

“…3 compares the reflected spectrum of a simulated FBG sensor under the non-uniform strain field depicted in Fig. 2a, along with its approximation given by (14). It can be seen that this approximation does not hold for the main lobe, but does hold for the wavelength region for which |λ − λ B | > λ th , where λ th is in the order of 1-2 nm which can be identified by setting a threshold level on the amplitude of the reflected spectra 4 .…”

Transducer Placement Option of Lamb Wave SHM System for Hotspot Damage Monitoring

“…Along with fiber-optic techniques such as Fiber-Bragg-Grating sensors [4,5], an ultrasonic guided waves-based solution such as those making use of Lamb waves is one of the promising techniques for SHM due to its long-range inspection capability up to several meters [6,7], which is suitable for monitoring large structures such as an aircraft fuselage. Also, in comparison to the FBG technique, Lamb wave SHM sensors typically require less complicated installations.…”

Analysis of the Side-lobes of FBG Reflection Spectra From Matrix Cracks in Composites

“…In addition, there has recently been an increased interest in using FBG sensors for the detection of impact damages. This can be accomplished via dynamic measurements of the Bragg wavelength shifts of the FBG at the time of the impact [2], or by analysing the static response of the FBG after the event [3]. This current study belongs to the latter group.…”