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National Repository of Grey Literature 2 records found  Search took 0.00 seconds. 
On finite element modelling in time reversal problems
 Mračko, Michal ; Kober, Jan ; Kolman, Radek ; Převorovský, Zdeněk ; Plešek, Jiří ; Masák, Jan ; Kruisová, Alena
In this paper we analyse suitability and accuracy of computational techniques in time reversal applications based on finite element method (FEM) for detection and localization of defects, cracks or other acoustic emission sources in bodies and structures. As it is known, a classical explicit integration scheme - central difference is reversible. The central difference scheme as a time integrator is widely used for linear and nonlinear finite element analyses and it is also implemented in commercial and open-source finite element software. In the paper properties of the explicit FEM in time reversal problems are studied and analysed. We use the standard Galerkin FEM formulation with linear shape functions, one-point Gauss integration and lumped mass matrix. Loading by the Ricker pulse was applied for modelling of the acoustic source in an elastic square domain. A special attention is paid to the choice of boundary conditions in reverse problem which keep the reversibility of problems of interest. Finally, we show the quality of refocusing of the original acoustic source.
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In situ calibration of acoustic emission sensors
 Kober, Jan ; Převorovský, Zdeněk
Calibration of acoustic emission (AE) sensors is recommended when comparing results of separate experiments or when studying frequency content of AE events. However conventional methods of AE sensor calibration require a reference sensor and/or special test specimen, equipment which is not readily available for most. Furthermore the calibration results are only approximately transferrable to practice, because they depend on bonding conditions and mechanical properties of the medium. A reference-free in situ method of sensors frequency responses determination based on standardized reciprocal calibration and time reversal method is proposed.
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