1,720,973 research outputs found
Review of digital image correlation application to large-scale composite structure testing
No full textThis study reviews the recent progress in the application of digital image correlation (DIC) to testing composite structures with an order of size magnitude of meters. The DIC technique has gained wide popularity in materials and structural testing due to the merit of being full-field and non-contact compared to conventional point-wise measurement techniques. This study focuses on the DIC application to large-scale composite structure testing. Experimental setup requirements, measurement capabilities, and the associated challenges are thoroughly reviewed and analyzed. Typical applications found in the literature are from wind energy and aerospace sectors for displacement and strain measurements under static loading and operational modal analysis in dynamic structural tests. The remaining challenges along with their possible solutions are discussed and summarized in this work to shed light on future research needs on testing large-scale composite structures using the DIC technique
Control of damage‐sensitive features for early failure prediction of wind turbine blades
No full textThe current study focuses on early prediction of structural failure of a composite wind turbine blade (WTB) using acoustic emission (AE) and strain measurement. The structural response of a 14.3-m blade with embedded artificial defects is investigated under fatigue loading in flapwise direction. The fatigue loading is realized in several successive portions until structural failure. Strain and acoustic emission signals from each portion are recorded. The goal is to explore damage-sensitive features (DSFs) derived from acoustic emission and strain signals that would be suitable for early indication of blade failure under fatigue. These features include modal characteristics of strain time history, such as natural frequencies, damping ratios, and modal amplitudes. Acoustic emission features explored in this study comprise average frequency centroids based on an amplitude and absolute energy and gradients of cumulative energy curves. Changes of these features before failure relative to the previous loading portion are calculated and compared among different sensor locations with a twofold goal—firstly, to find the features that are the most sensitive to damage accumulation and, secondly, to find a location with the largest relative changes, thus enabling damage localization. The results show that strain and AE signals are correlated well in terms of pinpointing to a location of the largest aggregation of defects. This study gives recommendations of the most efficient feature combination of different measurements for reliable structural health monitoring of wind turbine blades
Wavelet Transform Based Damage Detection in a Plate Structure
No full textAbstractA 2-dimensional wavelet transform algorithm employing isotropic Pet Hat wavelet is used to locate the area of damage in a numerically simulated aluminium plate model. To study the advantages and limitations of proposed method, signals of vibrational mode shapes of the plate are reduced by integer numbers to study the performance of algorithm at various sensor densities. Results suggest that the lowest scale of selected wavelet function yields the best damage identification results with a damage location likelihood of more than 98%
Thermographic data analytics-based damage characterization in a large-scale composite structure under cyclic loading
No full textLarge-scale composite structures such as aircraft wings and wind turbine blades undergo cyclic loading in operation. In-service damage often generates excessive heat due to material frictions and it could be detected by thermography. This study develops a methodology to quantitatively analyze such structural damage based on thermographic data analytics. A full-scale composite wind turbine blade is inspected using passive thermography when it is subject to cyclic loads in laboratory. The damage region is identified from thermographic images and it is tracked automatically using image processing. The damage region is subsequently characterized on both overall and detailed levels. The change of the damage status versus fatigue cycle number is analyzed and the information regarding the growth of the damage area and the damage severity is provided. The initiation and the progress of damage are investigated based on the temperature and the enthalpy change in the damage region. This study provides a viable solution for efficient structural health monitoring and damage prognosis of large-scale composite structures under cyclic loading
Mode shape curvature squares method for crack detection in railway prestressed concrete sleepers
Get PDFThis unprecedented study aims to demonstrate the potential to locate crack damage and severity in full-scale railway prestressed concrete sleepers. The dynamic mode shape curvature squares method has been utilised. This approach adopts structural deflection shapes extracted from experimental modal analysis using an impact excitation. The railway concrete sleepers are exposed to the first crack and 1.5 times above the first-crack loads using experimental setup in accordance with the British Standard (for benchmarking purpose). It is found that the first cracking of the sleepers has caused non-significant stiffness reduction of the structural component evidenced from the fact that the natural frequency shifts are only few percent and no visible differences in deflection mode shapes are observed. In addition, the mode shape curvature alone cannot indicate the crack establishment in the railway sleepers. However, a relatively sparse wireframe for deflection shapes enable the plausible density of sensor grids that can be further analysed for damage detection. In this paper, the curvature square approach has been developed to quantify and locate the damage in the railway sleepers. The standardized damage index distributions and subsequent thresholding with different levels of confidence of damage localization have been firstly developed to enhance the accuracy of crack localization. It is found that accurate locations of cracks mostly in the mid span of the sleepers can be reasonably detected in accordance with the actual crack measurements from the experimental data. The novel insight into this approach can enhance the new development of on-board technology for railway sleeper crack detection using operational modal signals
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
Influences of surface abrasions on dynamic behaviours of railway concrete sleepers
No full textBy nature, railway infrastructure is nonlinear, evidenced by its behaviors, geometry and alignment, wheel-rail contact and operational parameters such as tractive efforts. Based on our critical review, there exists no previous work that considers the degradation of railway concrete sleepers over time. In fact, the ballast angularity causes differential abrasions on the soffit or bottom surface of sleepers (especially at railseat zone). Furthermore, in sharp curves and rapid gradient change, longitudinal and lateral dynamics of rails increase the likelihood of railseat abrasions in concrete sleepers due to the unbalanced loading conditions. This paper presents a nonlinear finite element model of a standard-gauge concrete sleeper in a track system, taking into account the tensionless nature of ballast support. The finite element model was calibrated using static and dynamic responses in the past. In this paper, the influences of surface abrasions, including surface abrasion and soffit abrasion, on the dynamic behaviours of sleepers are firstly highlighted. The outcome of this study will improve the rail maintenance and inspection criteria in order to establish appropriate and sensible remote track condition monitoring network in practice
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