scholarly journals Adhesive Joint Integrity Monitoring Using the Full Spectral Response of Fiber Bragg Grating Sensors

Polymers ◽  
2021 ◽  
Vol 13 (17) ◽  
pp. 2954
Author(s):  
Chow-Shing Shin ◽  
Tzu-Chieh Lin
Keyword(s):  
Fiber Bragg Grating ◽  
Adhesive Joint ◽  
Spectral Response ◽  
Fatigue Loading ◽  
Lap Joints ◽  
Adhesive Joints ◽  
Bragg Grating ◽  
Integrity Monitoring ◽  
Joint Integrity ◽  
Spectral Responses

Although adhesive joining has many advantages over traditional joining techniques, their integrity is more difficult to examine and monitor. Serious structural failures might follow if adhesive joint degradation goes undetected. Available non-destructive examination (NDE) methods to detect defects are helpful in discovering defective joints during fabrication. For long-term monitoring of joint integrity, many of these NDE techniques are prohibitively expensive and time-consuming to carry out. Recently, fiber Bragg grating (FBG) sensors have been shown to be able to reflect strain in adhesive joints and offer an economical alternative for on-line monitoring. Most of the available works relied on the peak shifting phenomenon for sensing and studies on the use of full spectral responses for joint integrity monitoring are still lacking. Damage and disbonding inside an adhesive joint will give rise to non-uniform strain field that may chirp the FBG spectrum. It is reasoned that the full spectral responses may reveal the damage status inside the adhesive joints. In this work, FBGs are embedded in composite-to-composite single lap joints. Tensile and fatigue loading to joint failure have been applied, and the peak splitting and broadening of the full spectral responses from the embedded FBGs are shown to reflect the onset and development of damages. A parameter to quantify the change in the spectral responses has been proposed and independent assessment of the damage monitoring capability has been verified with post-damage fatigue tests.

Integrity monitoring of adhesively bonded joints via an electromechanical impedance-based approach

2017 ◽  
Vol 17 (5) ◽  
pp. 1031-1045 ◽  
Author(s):  
Yitao Zhuang ◽  
Fotis Kopsaftopoulos ◽  
Roberto Dugnani ◽  
Fu-Kuo Chang
Keyword(s):  
Fatigue Loading ◽  
Mechanical Tests ◽  
Lap Joints ◽  
Piezoelectric Sensors ◽  
Bonded Joints ◽  
Adhesively Bonded ◽  
Monitoring Method ◽  
Integrity Monitoring ◽  
Adhesively Bonded Joints ◽  
Electromechanical Impedance

Monitoring the bondline integrity of adhesively bonded joints is one of the most critical concerns in the design of aircraft structures to date. Due to the lack of confidence on the integrity of the bondline both during fabrication and service, the industry standards and regulations require assembling the primary airframe structure using the inefficient “black-aluminum” approach, that is, drill holes and use fasteners. Furthermore, state-of-the-art non-destructive evaluation and structural health monitoring approaches are not yet able to provide mature solutions on the issue of bondline integrity monitoring. Therefore, the objective of this work is the introduction and feasibility investigation of a novel bondline integrity monitoring method that is based on the use of piezoelectric sensors embedded inside adhesively bonded joints in order to provide an early detection of bondline degradation. The proposed approach incorporates (1) micro-sensors embedded inside the adhesive layer leaving a minimal footprint on the material, (2) numerical and analytical modeling of the electromechanical impedance of the adhesive bondline, and (3) electromechanical impedance–based diagnostic algorithms for monitoring and assessing the bondline integrity. The experimental validation and assessment of the proposed approach is achieved via the design and fabrication of prototype adhesively bonded lap joints with embedded piezoelectric sensors and a series of mechanical tests under various static and dynamic (fatigue) loading conditions. The obtained results demonstrate the potential of the proposed approach in providing increased confidence on the use of adhesively bonded joints for aerospace structures.

Effect of Impact-Fatigue on Damage in Adhesive Joints

2007 ◽  
Vol 347 ◽  
pp. 653-658 ◽  
Author(s):  
Juan Pablo Casas-Rodriguez ◽  
Ian A. Ashcroft ◽  
Vadim V. Silberschmidt
Keyword(s):  
Damage Evolution ◽  
Weight Ratio ◽  
High Strength ◽  
Fatigue Loading ◽  
Lap Joints ◽  
Adhesive Joints ◽  
Bonded Joints ◽  
Impact Fatigue ◽  
Adhesively Bonded ◽  
Low Velocity

In recent decades the use of structural adhesive joints in the aerospace industry has increased considerably thanks to their high strength-to-weight ratio, low stress concentration and capacity to join different adherends. There is increasing interest in damage due to low-velocity impacts produced in adhesively bonded components and structures by vibrating loads. This type of loading is known as impact fatigue. The main aim of this paper is to investigate damage evolution in adhesive joints subjected to impact-fatigue and to compare this with damage evolution in standard fatigue (i.e. non-impacting, constant amplitude, sinusoidal fatigue). In this work, adhesively bonded lap joints were subjected to multiple tensile impacts tensile and it was seen that this type of loading was extremely damaging compared to standard fatigue. A number of methods of studying damage evolution in bonded joints subjected to fatigue and impact fatigue loading have been investigated and various parameters have been used to characterise these processes. Two modifications of the accumulated time-stress model [1-4] are proposed and it is shown that both models provide a suitable characterization of impact-fatigue in bonded joints.

Applications of Fiber Bragg Grating in Strain Measurement of Concrete Bridge

2011 ◽  
Vol 368-373 ◽  
pp. 2286-2290
Author(s):  
Xian Xi Tang ◽  
Xian Zhou Tang ◽  
Yue Xu ◽  
Wei Guo
Keyword(s):  
Fiber Bragg Grating ◽  
Strain Gauge ◽  
Strain Measurement ◽  
Fatigue Loading ◽  
Good Effect ◽  
Bragg Grating ◽  
Fiber Grating ◽  
Concrete Bridge ◽  
Experimental Researches

In order to verify the role of fiber bragg grating strain gauge in strain measurement of concrete bridge, and the influence of concrete and steel strain properties by fatigue loading, the relevant experimental researches were carried out. The results indicated that the Fiber Bragg grating strain gauge could reflect the strain regularity of concrete and steel well; for the fiber grating strain rosettes inside the concrete, the pasting equipments of fiber gratings had a certain impact of the measurement effect. The fatigue loading had a certain impact of the properties of concrete and steel, in conditions of the same number of fatigue, the greater the stress amplitude the more obvious the effects. The results analysis shown that, fiber grating strain measurement innovated the means and methods of strain measurement in detailed structure of the concrete bridge, for the strain measurements of concrete bridge under fatigue loading, the FBG could still play very good effect.

scholarly journals Modeling and Simulation of Fiber Bragg Grating (Fbg) as A Strain Sensor

2017 ◽  
Vol 10 (2) ◽  
pp. 260-263 ◽  
Author(s):  
Muhammad Bin Jalil
Keyword(s):  
Refractive Index ◽  
Fiber Bragg Grating ◽  
Spectral Response ◽  
Grating Period ◽  
Applied Strain ◽  
Bragg Grating ◽  
Wavelength Shift ◽  
Fiber Grating ◽  
Spectral Reflectivity ◽  
Maximum Reflectivity

This study presents the modelling, simulation, and characterization of the Fiber Bragg grating (FBG) on maximum reflectivity, bandwidth, the effect of applied strain to the wavelength shift, ʎB and sensitivity of the wavelength shift with strain for optical sensing system. In this study, a commercial FBG with the center wavelength of 1550nm is used in order to measure the spectral response of FBG to strain. The parameters used in these simulations are the fiber grating length, L ranging from 1 to 10mm, the changes in refractive index, ∆n from 0.0002 to 0.0020, the effective refractive index, is 1.46 and the grating period of FBG,Λ for 530nm in the performance of FBG. The bandwidth and spectrum reflectivity are analyzed from the variation of refractive index and grating length. Simulations on the FBG are carried out using OriginPro 2016 and Microsoft Excel 2010 software. The Excel sheet is used to generate data and the OriginPro 2016 is used to generate the graphs. The results obtained indicates the variation in grating length and refractive index affect the spectral reflectivity and the bandwidth. In addition, results obtained show that the changes in the Bragg wavelength are due to an increase in length of the grating region which due to the applied strain.

scholarly journals A Temperature Independent Inclinometer Based on a Tapered Fiber Bragg Grating in a Fiber Ring Laser

Sensors ◽  
2021 ◽  
Vol 21 (9) ◽  
pp. 2892
Author(s):  
Weihao Lin ◽  
Shengjie Zhou ◽  
Liyang Shao ◽  
Mang I. Vai ◽  
Perry-Ping Shum ◽  
...  
Keyword(s):  
Fiber Bragg Grating ◽  
Tilt Angle ◽  
Ring Laser ◽  
Variable Temperature ◽  
Spectral Response ◽  
Bragg Grating ◽  
Fiber Ring Laser ◽  
Fiber Ring ◽  
Tapered Fiber ◽  
Compact Size

We demonstrate a new concept for an all-fiber inclinometer based on a tapered fiber Bragg grating (tFBG) in a fiber ring laser (FRL) with the capability of measuring the tilt angle and temperature simultaneously. The sensor performance is analyzed theoretically and investigated experimentally. The dependence of tilt angle on the spectral response in variable temperature conditions was measured. Two inclinometers with different lengths have been fabricated and characterized in FRL. The sensitivity is 0.583 dB/° and 0.849 dB/°, respectively, in the range of 0° to 90°. Thanks to the FRL system, narrow 3-dB bandwidth (<0.1 nm) and high optical signal-to-noise ratio (~60 dB) are achieved. The tFBG in the FRL system can be used for working as a temperature insensitive inclinometer. The results suggested that the proposed inclinometer has the advantages of compact size and convenient manufacture, enhancing its potential for application prospect.

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

2009 ◽  
Vol 79-82 ◽  
pp. 2067-2070 ◽  
Author(s):  
Ya Lin Guo ◽  
S.L. Ogin ◽  
T.F. Capell ◽  
A.M. Thorne ◽  
G.T. Reed ◽  
...  
Keyword(s):  
Elevated Temperature ◽  
Fiber Bragg Grating ◽  
Reasonable Agreement ◽  
Fatigue Loading ◽  
Bragg Grating ◽  
Bonded Joints ◽  
Front Position ◽  
Bonded Joint ◽  
Chirped Fiber Bragg Grating ◽  
Bonded Composite

Chirped fiber Bragg grating (CFBG) sensors were embedded within the adhesive bondline of single-lap CFRP-GFRP bonded composite joints. The effect of disbond propagation (as a consequence of fatigue loading) on the reflected spectra from the CFBG sensor has been studied. As the disbond propagates, thermal strains generated during the bonding of the joint at elevated temperature are released and, as a consequence, a peak in the reflected spectra of the CFBG sensor can be seen. Using a transparent GFRP adherend, it has been possible to demonstrate that there is reasonable agreement between the position of the peak in the reflected spectrum and the disbond front position in the bonded joint.

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