117,358 research outputs found
Impact 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
Analysis of Vibro-Acoustic Modulations in Nonlinear Acoustics Used for Impact Damage Detection – numerical and experimental study
No full textAnalysis of Nonlinear Vibro-Acoustic Wave Modulations Used for Impact Damage Detection in Composite Structures
No full textImpact 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
Investigation of low-frequency excitation amplitude on the effectiveness of nonlinear vibro-acoustic method used for damage detection
No full textTriple correlation for detection of damage-related nonlinearities in composite structures
No full textNonlinear effects in vibration responses are investigated for the undamaged composite plate and the composite plate with a delamination. The analysis is focused on higher harmonic generation in vibration responses for various excitation amplitude levels. This effect is investigated using the triple correlation technique. The dynamics of composite plate was modelled using two-dimensional finite elements and the classical lamination theory. The doubled-node approach was used to model delamination area. Mode shapes and natural frequencies were estimated based on numerical models. Next, the delamination divergence analysis was used to obtain relative displacements for delaminated plies. Experimental modal analysis test carried out to verify the numerical models. The two strongest vibration modes as well as two vibration modes with the smallest and largest motion level of delaminated plies were selected for nonlinear vibration test. The Fisher criterion was employed to verify the effectiveness and confidence level of the proposed technique. The results show that the method can be used not only to reveal nonlinearities, but also to reliably detect impact damage in composites. These resultsare confirmed using the statistical analysis
Damage imaging in composites using nonlinear vibro‐acoustic wave modulations
No full textThe paper deals with the application of nonlinear vibro‐acoustic modulation technique for detection and localization of impact damage in a laminated composite plate. An imaging procedure—based on the nonlinear vibro‐acoustic modulation sidebands—is proposed. The procedure relies on simultaneous low‐frequency modal and high‐frequency ultrasonic excitations. Laser scanning vibrometry is used to analyze the amplitude of modulation sidebands in vibro‐acoustic responses. This analysis is performed for different positions on monitored structure to reveal the location and shape of damage. The method is illustrated using a simple example of impact damage detection in a composite plate. The experimental damage detection results are compared with the results obtained from the previously used approach on the basis of higher harmonic generation. The proposed method demonstrates better ability to locate damage in these comparative tests without the need to increase the measurement bandwidth to the higher harmonics regime. The work shows that the local defect resonance analysis can improve damage detection results of both compared approaches
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
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