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Localization of continuous acoustic emission sources using time reversal procedure
Převorovský, Zdeněk ; Krofta, Josef ; Kober, Jan ; Chlada, Milan
A new solution with the help of Time Reversal (TR) signal processing approach is suggested in this paper. It allows planar location of burst AE sources under high background noise using only one transducer, and continuous AE sources with two transducers, both under high background noise from other sources. TR procedure was in this approach applied to long random noise signals for the first time. Suggested method was verified by means of experimentally simulated AE sources on a steel plate and tube. Source location results certified high robustness of suggested approach. Certain disadvantage of the new method is requirement of detailed scanning of region around a presumed source. Scanning may be eliminated if we use numerical simulations with TR signals put into a computer model of the structure. Localization accuracy of suggested procedure (approx. 1 mm) is better than the wavelength and transducers aperture.
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Optimization of sensor selection for acoustic emission source location
Chlada, Milan ; Převorovský, Zdeněk
Similarly to Global Positioning System (GPS), location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to mathematically express its measure and compare particular sensor configurations in accordance with desired location precision, recently proposed method brings extended possibilities for detection of critical regions characterized by strong sensitivity of location results to signal arrival time changes or errors. Analogically to GDOP parameter it yields the sensitivity map available even for non-continuous or anisotropic materials. During the computation it uses the algorithm for finding the shortest ways in discretely defined bodies, which furthermore enables to view the problem through the so-called similarity and ambiguity maps.
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Mapping of problematic regions in AE source location
Chlada, Milan ; Převorovský, Zdeněk
Similarly to Global Positioning System, location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to mathematically express its measure and compare particular sensor configurations in accordance with desired location precision, recently proposed method brings extended possibilities for detection of critical regions characterized by strong sensitivity of location results to signal arrival time changes or errors. Analogically to GDOP parameter it yields the sensitivity map available even for non-continuous or anisotropic materials. During the computation it uses the algorithm for finding the shortest ways in discretely defined bodies, which furthermore enables to view the problem through the so-called similarity and ambiguity maps.
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Verification of diagnostic device using NEWS methods
Chlada, Milan ; Krofta, Josef ; Kober, Jan
Within the framework of the project „Verification of diagnostic device using NEWS methods“ supported by SIC, several calibration tests of newly developed apparatus for non-destructive testing of materials by NEWS (Non-linear Elastic Wave Spectroscopy) methods were realized. The report summarizes the results of characteristics measuring for case of particular components of the device and the demonstration tests of defect detection in selected structure parts.
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Condition monitoring of thrust ball bearings using continuous AE
Chlada, Milan ; Nohal, L. ; Převorovský, Zdeněk
Fast and reliable analysis of continuous AE recorded during endurance tests on flat washer parts reliably simulating critical rolling contact fatigue of the full-scale bearings is presented in the paper. Two channels of continuous AE signal were partially recorded within whole specimen lifetime tests and compared with other experimental parameters as vibration rate or temperature. As an alternative to classical spectrogram analysis, we proposed to use histograms of time intervals between threshold amplitudes crossings in various frequency bands represented by the wavelet decomposition. Results obtained on long-time records are discussed, illustrating advantages of proposed AE signal processing, which can be done in real time to observe the processes before the onset of the final damage on the surface of the specimen more precisely than vibrodiagnostics.
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The System for Automatic Location of Impacts
Chlada, Milan ; Kober, Jan ; Převorovský, Zdeněk ; Krofta, Josef
The report deals with the automatic target system for on-line evaluation of shooting precision based on acoustic emission (AE) method, known from the field of non-destructive testing as an approach for location of material defects. Since the bullet stroke on a steel plate can be considered as an AE source, the method can be included in a target system consisting of impact plate, AE sensors and AE measuring system with implemented advanced location algorithms. Whole system can be sized and matched to specific customer needs. At the end of the report, the real demonstration of the system is shown.
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Shortest Ways Finding in Discrete Bodies
Chlada, Milan ; Převorovský, Zdeněk
Estimation of the shortest wave-path is a crucial task not only in the field of acoustic emission (AE) source location. Recently designed method for solving the problem was inspired by Huygens' principle as easy to implement alternative suitable for discretized 2D or 3D 'bitmap' pictures of a body. This approach also enables tracing of elastic waves propagating in structures of complicated shapes without mathematical models and collecting sufficient amount of representative data for AE source location algorithms based on database searching or artificial neural networks. The new method already showed its advantages and potentialities in practical tasks as discussed.
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Multilevel Analysis of Continuous Acoustic Emission Records
Chlada, Milan ; Převorovský, Zdeněk
The latest acoustic emission (AE) systems provide continuous recording of high-frequency signals registered during longtime monitoring of various processes in materials. Recorded data represent extremely large amount of information to analyze, however, it reflects the health of the structure. Therefore, in the last years the attention is paid to the diagnostic method of continuous AE also as a part of Structural Health Monitoring (SHM) systems. For example it can disclose the early damage phases (cracks) or certain imperfections in rotating gearboxes, the leakage of liquids from pressure vessels and many other material defects. This method requires new signal processing and analysis approaches, which are different from the burst AE. The paper deals with the analysis of continuous AE, recorded during the test of renovated gearbox at different flight modes. As an alternative to classical spectrogram, so-called multilevel countogram based on the signal wavelet decomposition is proposed and discussed.
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