Detection of defects in as manufactured GFRP–GFRP and CFRP–CFRP composite bonded joints using chirped fibre Bragg grating sensors

Abstract

Chirped fibre Bragg grating (CFBG) sensors have been embedded in composite coupons which have been used to form one half of single lap bonded joints. The bonded joints have been made with deliberately included defects, consisting of either a PTFE insert or an air gap, and the sensors have been used to detect the presence and location of the defects. The experimental results, and the modelling, show that defects in both GFRP-GFRP joints and CFRP-CFRP joints can be detected by the embedded CFBG sensors, though it is easier to detect defects in the lower stiffness (GFRP) joints.

An Experimental and Numerical Study on the Use of Chirped FBG Sensors for Monitoring Fatigue Damage in Hybrid Composite Patch Repairs

“…Palaniappan et al [ 11 ] performed a similar study but using glass fibre reinforced polymer (GFRP) cross-ply laminates showing the capability of the technique to detect the initiation and growth of delaminations. Embedded CFBG sensors have also been used in single-lap joints to detect delamination and manufacturing defects in the form of cracks or voids [ 12 , 14 , 15 ]. For example, Palaniappan et al [ 14 ] embedded a CFBG sensor in one of the adherends of a GFRP lap-joint; the results showed good agreement between the dip in the spectrum and the actual position of a delamination front growing under fatigue loading.…”

Effect of Disbond Propagation on the Reflected Spectra of CFBG Sensors Embedded within the Bondline of Composite Bonded Joints

“…Of the various non-destructive evaluation methods available [1], chirped fibre Bragg Grating (CFBG) sensors have been investigated recently for damage monitoring in bonded composite joints [e.g. [2][3][4]. One important advantage of this kind of sensor is that it can both detect and monitor damage development in bonded joints.…”

“…Schematic of joint geometry, where LW and HW indicate the low and high wavelength ends of the CFBG, respectively The optical interrogation system, which includes a broadband source and an optical spectrum analyser to record the spectra reflected by the CFBG, has been described in detail elsewhere [e.g. [2][3][4]. The joint was subjected to fatigue loading using a computer-controlled servo-hydraulic testing machine (Instron 1175) with a peak load of 8 kN, an R-value of 0.1, and a sinusoidal waveform with a frequency of 6 Hz.…”

“…The stacking sequence of the cross-ply GFRP and CFRP laminates were [0 4 /90 2 ] s and [0 2 /90/0 2 ] s , respectively. Details of the GFRP and CFRP laminate fabrication are given in references [2][3][4]. The joint was bonded with an epoxy adhesive, AV119, cured at 120 Figure 1.…”

On the use of a CFBG sensor to monitor scarf repairs of composite panels

“…Chirped fibre Bragg grating sensors have been shown to be able to monitor delamination initiation and growth in single-lap joints when embedded within one of the adherends (Palaniappan et al 2007;Palaniappan et al 2008;Capell et al 2009). The purpose of this work is to investigate whether such sensors can be used to monitor the initiation and propagation of damage in a scarf-repaired transparent GFRP specimen subjected to flexural fatigue loading.…”