Detection of Damage in CFRP by Wavelet Packet Transform and Empirical Mode Decomposition: an Hybrid Approach
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Detection of Damage in CFRP by Wavelet Packet Transform and Empirical Mode Decomposition: an Hybrid Approach Claudia Barile 1 & Caterina Casavola 1 & Giovanni Pappalettera 1 & Carmine Pappalettere 1 & Paramsamy Kannan Vimalathithan 1 Received: 19 March 2020 / Accepted: 19 June 2020/ # Springer Nature B.V. 2020
Abstract
The integrity of the CFRP specimens is tested using acousto-ultrasonic testing method. To validate the acousto-ultrasonic test mode, the specimens are tested before and after a Barely Visible Impact Damage induced by an impactor. A special model is created to use both Wavelet Packet Transform and Empirical Mode Decomposition, for decomposing the recorded waveforms. This mode also enables the reconstruction of the decomposed waveforms, discarding the residual signal in the parent waveform, and calculates the energy associated with each frequency band of the reconstructed signal. By using the percentage of energy recovered by the receiver compared to the signal sent through the specimen, the integrity of the specimens is identified. Moreover, the properties of each specimen and the extent of its damage, albeit qualitatively along the longitudinal and transverse directions can also be assessed by using this technique. Keywords Acousto-ultrasonic . CFRP . Wavelet Packet Transform (WPT) . Empirical Mode Decomposition (EMD) . Barely Visible Impact Damage (BVID)
1 Introduction Acoustic Emission (AE) technique is one of the most powerful non-destructive evaluation methods used for damage characterization of materials and structures. The basic principle of the AE technique is that it records the elastic waves released during the deformation of a material/structure under loading. Thus, it is termed as a ‘passive’ non-destructive evaluation technique. It provides information about the damage progression in material under its entire loading history [1]. * Claudia Barile [email protected]
1
Dipartimento di Meccanica Matematica e Management, Politecnico di Bari, Via Orabona 4, 70125 Bari, Italy
Applied Composite Materials
During the acoustic emission, the elastic waves released under loading must propagate through the material before reaching the receiving piezoelectric sensor. These stress waves are transient in nature and can take both symmetric and asymmetric forms in time-frequency domains [2, 3]. Depending on the geometry of the structure, rigidity of the wave propagation direction, material properties of the propagating medium and the type of waveform, these elastic waves lose their energy in the time-frequency domain before reaching the sensor. This loss in energy of the recorded waveform becomes the basis of Acousto-Ultrasonic testing. Unlike the conventional AE technique, this technique does not rely on the elastic waves generated by the energy released during deformation. Instead, the source for the signal is an external pressure wave simulated on the surface of the material/structure [4, 5]. These pressure waves are transformed into structural stress waves in the material and are recorded
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