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NDE detection of manufacturing defects in composite bonded joints using CFBG sensors
No full textThis paper reports the use of chirped fibre Bragg grating (CFBG) sensors to detect defects introduced during the bonding of composite joints. The single-lap joints were made from transparent GFRP cross-ply composites which had a CFBG sensor embedded within one of the two adherends during the manufacturing stage. Joints with defects simulated using PTFE or introduced real air-gaps have been investigated. The sensors were interrogated with no load on the joints and also under a moderate quasi-static load. For the joints with PTFE “defects”, the perturbations observed in the reflected spectra provided a clear indication of the location of the defects and were in very good agreement with modelling predictions. Changes in the reflected spectra for the air-gap defects also provided an indication of the location of the defects and the spectrum changes were in reasonable agreement with modelling predictions. However, further work is required to establish the limitations of the technique for air-gap defects
Disbond growth detection in composite-composite single-lap joints using chirped FBG sensors
Get PDFAdhesively 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 15–60 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 disbond growth
No full textComposite-composite or composite-metal bonded joints, are used in various industries and applications. The difficulty with any bonded construction with regard to structural integrity monitoring is, of course, that the bonded structure cannot be disassembled easily. Various NDE (non-destructive evaluation) techniques have been suggested to monitor bonded joints based on ultrasonic, acoustic, thermal and backface strain measurements [e.g. 1-3]. Among NDE optical techniques suggested, the use of uniform fibre Bragg grating (FBG) sensors has been the most widely favoured, with a number of demonstrations available in the literature for monitoring bonded joints, repairs and structures [e.g. 4-6]. In addition, chirped fibre Bragg grating (CFBG) sensors have been investigated more recently for damage monitoring in composite materials, bonded joints and sandwich structures (e.g. [7-11])
Reflected spectra prediction for chirped fibre Bragg gratings used for disbond detection in composite/composite bonded joints
No full textIn this paper it is shown that a chirped fibre Bragg grating sensor embedded within a composite adherend can be used to monitor disbond initiation and propagation in an adhesively bonded single lapjoint. Characteristic changes in the reflected spectra from the sensor indicate both disbond initiation and the current position of the disbond front to within about 2 mm (a distance which depends on adherend material and sensor position in relation to the adhesive bondline). When the sensor extends the full overlap length, disbond initiation from either end of the overlap can be monitored. The results have been modelled using a combination of finite-element analysis and commercial software for predicting FBG spectra; the predicted spectra are in very good agreement with experiment. The CFBG sensor technique could provide the basis for monitoring a wide range of bonded joints and structures where one adherend is a composite material
The use of a CFBG fibre optical sensor to detect disbond development in composite/composite and metal/composite adhesively bonded joints
No full textThis paper describes a novel technique to monitor disbond initiation and propagation in both composite-composite and metal-composite adhesively bonded joints using chirped fibre Bragg grating (CFBG) sensors embedded within fibre-reinforced composite adherends. Characteristic changes in the reflected spectra from the sensors indicate both (a) disbond initiation (due, for example, to fatigue loading) and (b) the current position of the disbond front (to within about 2 mm). For composite-composite bonded joints, the reflected spectra are recorded with the joint under a small load (in practice, this could be the self-weight of the structure). In the case of a metal-composite joint, the difference in the coefficient of thermal expansion between the adherends is sufficient to enable disbond propagation to be monitored when the joint is unloaded. The experimental results have been modelled using a combination of finite-element analysis and commercial software for predicting FBG spectra, with very good agreement between the experimental observations of the reflected spectra and the predicted spectra, for disbonds of different lengths
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Detection of defects in as manufactured GFRP-GFRP and CFRP-CFRP composite bonded joints using chirped fibre Bragg grating sensors
No full textChirped 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. <br/
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