1,354,426 research outputs found
Impact damage detection in smart composites using nonlinear acoustics - Cointegration analysis for removal of undesired load effect
No full textThe paper presents a reliable methodology - based on nonlinear acoustics - for impact damage detection in composite materials. The nonlinear vibro-acoustic wave modulation technique is used to detect damage. The problem of operational variability of the method with respect to the selection of frequency and amplitude of low-frequency (LF) modal excitation is investigated. This problem is addressed using the concept of stationarity of time series of vibro-acoustic data. Cointegration analysis is employed to compensate for the effect of variable operational conditions associated with LF modal (or vibration) excitation in nonlinear vibro-acoustic wave modulations. Analysis of stationary statistical characteristics of vibro-acoustic responses - after cointegration analysis - are used for damage detection. The proposed method is validated using vibro-acoustic data from laminated composite plates and composite sandwich panels. The results demonstrate that the proposed approach can effectively compensate for the effect of LF modal excitation on nonlinear vibro-acoustic wave modulations and detect the damage more accurately and robustly than the existing nonlinear acoustics based on the analysis of modulation sidebands
Impact damage detection in laminated composites by non-linear vibro-acoustic wave modulations
No full textThe paper presents an application of nonlinear acoustics for impact damage detection in composite laminates. Two composite plates were analysed. A low-velocity impact was used to damage one of the plates. Ultrasonic C-scan was applied to reveal the extent of barely visible impact damage. Finite element modelling was used to find vibration mode shapes of the plates and to estimate the local defect resonance frequency in the damaged plate. A delamination divergence study was performed to establish excitation parameters for nonlinear acoustics tests used for damage detection. Both composite plates were instrumented with surface-bonded, low-profile piezoceramic transducers that were used for the high frequency ultrasonic excitation. Both an arbitrary frequency and a frequency corresponding to the local defect resonance were investigated. The low-frequency modal excitation was applied using an electromagnetic shaker. Scanning laser vibrometry was applied to acquire the vibro-acoustic responses from the plates. The study not only demonstrates that nonlinear vibro-acoustic modulations can successfully reveal the barely visible impact damage in composite plates, but also that the entire procedure can be enhanced when the ultrasonic excitation frequency corresponds to the resonant frequency of damag
Analysis of Vibro-Acoustic Modulations in Nonlinear Acoustics Used for Impact Damage Detection – numerical and experimental study
No full textInvestigation of low-frequency excitation amplitude on the effectiveness of nonlinear vibro-acoustic method used for damage detection
No full textImpact damage detection in light composite sandwich panels
No full textThe paper presents a comparative study on impact damage detection in light composite sandwich panels. Three different nondestructive testing methods were used to characterize damage in a test specimen that resulted from a controlled low velocity impact event. The analyzed test methods include the ultrasonic c-scan, vibrothermography and shearography. All considered techniques were positively verified for detecting damage in a sandwich panel. The paper gives details about the experimental procedures and equipment required to perform the tests
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
No full textWe 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
Assessing the scaling subtraction method for impact damage detection in composite plates
No full textThe scaling subtraction method (SSM) is a non-destructive measurement approach used to extract nonlinear features from the elastic response of a structure. As such it can be used for damage detection purposes by identifying nonlinearities that may result from the presence of micro cracks or inclusions in granular and metallic materials. The effectiveness of such a technique to detect the presence of damage modes typical of laminated composite materials has not been yet assessed. With the purpose of filling this gap, in this paper the SSM is applied to inspect two laminated composite plates with different sizes, impact positions and sensor arrangement. Intact and damaged specimens are tested under harmonic excitations of different amplitude and frequency (the latter selected among the ultrasonic natural frequencies of the two plates). For each excitation case the recorded vibration signals are subtracted from the linearly rescaled reference signals and the SSM nonlinear indicators are calculated. The sensitivity of the method to the presence of damage is assessed in different sensor-receiver scenarios as well as for different excitation frequency and amplitude levels. Finite element numerical investigations are also performed to make comparisons with the experimental results
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