Disbond growth detection in composite–composite single-lap joints using chirped FBG sensors

Abstract

Adhesively bonded composite-composite single-lap joints, with cross-ply GFRP adherends, have been cyclically loaded to initiate disbonding at either end of the overlap length. Disbond initiation and growth have been monitored using a combination of in situ photography (the joint is transparent) and a single chirped fibre Bragg grating (CFBG) sensor embedded within one composite adherend (with the low-wavelength end of the sensor adjacent to the cut end) and not in the adhesive bondline. Sensors having the same spectral bandwidth (20 nm), and lengths in the range 15 mm to 60 mm have been tested. The experimental results have been modelled using a combination of finite-element analysis and commercial software for predicting FBG spectra, and the predictions are in very good agreement with the experimental results. In all cases, it has been shown that the position of the disbond front can be located using the CFBG sensors with a precision of about 2 mm.

The use of chirped fibre Bragg grating sensors to monitor delaminations in composite materials and structures

“…The consequence is a local dip in the spectrum (since the reflected intensity is a function of the local density of the grating spacings) and an increase of the intensity at higher wavelengths, as the increased grating spacings add to the grating spacings already present towards the higher wavelength end of the sensor. Finite-element analysis to predict the strain distribution along the sensor length, and subsequent use of the commercial software OptiGrating, enabled a prediction of the expected reflected spectrum to be made which was in very good agrement with the experimental results (Palaniappan et al 2008). In this example, the adhesive used to produce the bonded joint was cured well above room temperature (at 120 0 C), but since the GFRP adherends were identical, no thermal strain mismatch occurs between the adherends.…”

“…The disbonding, or delamination, of a bonded composite joint can be readily monitored using a CFBG sensor embedded within one adherend (Palaniappan et al 2005;2008). Figure 2 shows a schematic of two GFRP adherends bonded together, over a 60 mm length, to form a single-lap joint.…”

Fabrication of a Multiplexing Sensor Probe for Measuring the Blade Deflection of a Wind Power Generator

“…그러므로 본 연구에서는 FBG 센서에 에폭 시 패키징 처리를 하여 광섬유의 파손 및 온도에 대한 민감도를 개선한 센서 탐촉자를 제작하고자 한다. [14][15][16] . 되돌아온 파장은 서큘레이터를 통하여 파장 측정기로 측정하면 된다.…”

Use of a surface-mounted chirped fibre Bragg grating sensor to monitor delamination growth in a double-cantilever beam test

“…Chirped FBG (CFBG) sensors embedded within composite materials have been shown to be able to monitor delamination growth in single-lap joints [6][7][8], where the 3 changes in the reflected spectra due to delamination growth are much easier to interpret than for uniform FBGs. Whereas unstrained uniform FBG sensors have a constant periodic variation of the refractive index within the fibre core (the "grating" spacing), the CFBGs used in this work have a linearly increasing grating spacing.…”