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Elastodynamic Properties and Signal Propagation in Materials within Time Reversal Acoustics
Farová, Zuzana ; Převorovský, Zdeněk ; Kůs, V. ; Dos Santos, S.
In this paper we present related parts of elastodynamic theory, which are a keynote for the wave propagation through the medium. We describe the basic material characteristics - strain tensor and stress tensor, also we provide the relations of these tensors and describe the derivation of the well-know Lame's parameters. Further, we deal with the theory of Green functions, its properties, and its form for di®erent sources. Finally, we propose and explain the so-called experimental deconvolution, quite newly developed technique, based on time reversal acoustics with the knowledge of Green function and using the Fourier transform.
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Structural Health Monitoring in aerospace and civil engineering supported with two ultrasonic NDT methods - AE and NEWS
Převorovský, Zdeněk ; Krofta, Josef ; Farová, Zuzana ; Chlada, Milan
Structural Health Monitoring (SHM) becomes today an important technology improving reliability and safety of aeronautical and civil structures. Combining of two ultrasonic NDT methods - Acoustic Emission (AE) with Nonlinear Elastic Wave Spectroscopy (NEWS) - in SHM systems brings many advantages. AE enables real-time detection and localization of initiation and progression under operational stimulations, and NEWS methods provide retrieval of structural faults and complete information on AE sources. Examples of a complex SHM system design for critical parts of both aircraft and building roofs are discussed in this paper. The NEWS pseudo-tomography procedure, based on Time Reversal Mirrors (TRM) with Excitation Symmetry Analysis Method (ESAM), enabled zone-location of initiating defects, not detectable by other classical NDT procedures.Our results reflect good robustness of both techniques, and support their helpfulness in SHM of aircraft and building structures.
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Experimental Signal Deconvolution in Acoustic Emission Identification Setup
Farová, Zuzana ; Převorovský, Zdeněk ; Kůs, V. ; Dos Santos, S.
Identification of acoustic sources is a great deal and the most important problem emerging in nondestructive testing. We present the basics of time reversal (TR) Acoustic Emission (AE) principle and point out the advantages of AE nondestructive testing for localization and classification of acoustic sources. This approach provides the tool for the defect localization by means of the reversal wave focusing in nonlinearity position in the material under consideration. Also, using TR operator to AE signal, we obtain convolutional signal in the closest neighborhood of acoustic source, which gives us the pure image of the real characteristics of AE source after deconvolution process applied to the signals detected.
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