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Development of a New Generation of Devices with Advanced Diagnostics for Determining Contact Degradation
Dvořáček, Jiří ; Hájek, Karel (referee) ; Náhlík, Luboš (referee) ; Pazdera, Luboš (referee) ; Mazal, Pavel (advisor)
The thesis proposes a methodology for damage identification of thrust bearings using acoustic emission method. The work is the way of the hydraulic loading of specimens and thrust bearings with programmable settings severity and duration of load cycles during contact fatigue tests at stations Axmat. They are designed structural adjustment elements (waveguides) to capture the acoustic emission signal selected apparatus, including the modification of software to capture the data. At the described experiments is verified functionality of the circular test specimens and axial bearings . Part of this work is to propose a new methodology for identifying early stages of contact fatigue using a combination of diagnostic methods.
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Design of Acoustic Emission Detector
Velecký, Petr ; Křenek, Ladislav (referee) ; Rubínová, Dana (advisor)
This bachelor thesis deals with design of acoustic emission detector, a professional device for leak detection in pneumatic systems. The aim was to create an intuitive device that would have a distinct appearance and respect all ergonomic, technical and aesthetic requirements. Manipulation with the device was made easier.
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Modernization of R-mat test stations
Papaj, Lukáš ; Dočkal, Aleš (referee) ; Mazal, Pavel (advisor)
The aim of the thesis is to reconstruct obsolete R-mat test stations, which are used for rolling contact fatigue tests of material, which are still of interest from industry. It was necessary to replace the original control electronics with a new industrial computer to allow use modern sensors and automate the entire test process. At the same time, the measurement was supplemented by an acoustic emission method, which can also record the development of damage. Design modifications have been made that allow the installation of all new sensors. The main method for evaluating the tests is vibrodiagnostics, which is supplemented by the acoustic emission method. With the help of several experiments, the shortcomings of the new control system were identified, some parameters were designed, and the main functionality of the modernized R-mat station was verified. According to the proposed parameters and the identified shortcomings, the control system was modified, and a script was created, which is used to evaluate the test. It is still possible to perform rolling contact fatigue tests of the material on the modernized equipment, and thanks to the modernization of the electronics, it is possible to test completely new methods of test evaluation.
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Primary Calibration of Acoustic Emission Sensors
Keprt, Jiří ; Mazal, Pavel (referee) ; Hájek, Karel (referee) ; Beneš, Petr (advisor)
The aim of the doctoral thesis is the problem of the primary calibration of acoustic emission sensor. In the introductory chapters, there are the results from the study of literature in field of AE and primary calibration of AE sensor summarized. The practical part of the thesis is aimed on realization of the primary calibration of AE sensors by different methods. The standardized methods of step function calibration and reciprocity calibration were practically realized as a part of the research on the same aparature. The method of reciprocity calibration with wideband excitation was practically realized too. The comparison between results from each used method was realized and the influences of the different sources of uncertainty and the different configuration of the calibration aparature on the step function calibration and the reciprocity calibration were determined. The uncertainties were determined for each realized methods. The recommendations for the calibration by the different methods on the available calibration aparature were presented. All the proceses of the reciprocity primary calibration was automated by the programmed software and the channel switcher. The UT 1000 (s.n. 169) by Physical Acoustic Corporation was used as the calibrated sensor for the comparison of the results of the calibrations.
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Scanning of acoustic emission signal by using waveguides
Bančák, Matej ; Vlašic, František (referee) ; Mazal, Pavel (advisor)
Bachelor thesis is focused on the issue of scanning acoustic emissions from the surface of solid body and scanning with the help of acoustic waveguide placed on the solid body. The work includes the review of the present ways of scanning acoustic emissions, options of installation waveguide and propagation of waves. The practical part is focused on the experiment, which compares measured values from the surface of the test body and from the waveguide. The measurement was realized on steel of the standard quality for using a measuring instrument Dakel Xedo. The next object of this work was try to attenuate the reflected signal, which is produced by the action of force on the test body.
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Wavelet transform and characterization of acoustic signal emision for cluster analysis
Blažek, Petr ; Holcman, Vladimír (referee) ; Sedlák, Petr (advisor)
This work describes the usage application of wavelet transform for on characterization of acoustic emission signals in cluster analysis. Acoustic emission, which are among the passive non-destructive methods, offering a huge potential due to quantization evaluating their options, such as localization and characterization of emission sources, i.e. wide spectrum of degradation processes in the material. In this work, I focused on testing the input parameters AE, selection of a suitable mother wavelet in the application of DWT and WPT for characterization of AE sources and the selection of a suitable mother wavelet noise reduction when using DWT.
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Measurement of Parameters of Piezoelectric Active Elements for Acoustic Emission Sensors
Fialka, Jiří ; Erhart,, Jiří (referee) ; Sedlák, Petr (referee) ; Beneš, Petr (advisor)
The doctoral thesis discusses the measurement of parameters of piezoelectric (PZT) materials and the influence of temperature on their stability. In the introductory sections, the author briefly explains the piezoelectric effect and its use; simultaneously, methods for the preparation of piezoelectric materials and the measurement of their properties are presented to illustrate the analyzed problem. The experimental part of the thesis describes the procedure of measuring and calculating the complete matrix of material coefficients from samples of PZT ceramics. The applied set of piezoelectric samples complying with relevant European and world standards was made in the form of thin plates, thin discs and cylinders, via gradual modification of the large disc. The NCE51 and/or the older PCM51 ceramics obtained from the company Noliac Ceramics were used in determining the complete matrix and describing the measurement method. Both these types are soft piezoceramics composed from a solid solution of lead zirconate and lead titanate with the general chemical formula of Pb(Zr1-x,Tix)O3. The real crystallographic structure and chemical composition of the samples were confirmed by X-ray diffraction spectroscopy and energy dispersive spectroscopy (EDS), respectively. The frequency method was used for the measurement and calculation of all material coefficients. An Agilent 4294A impedance analyzer and a set of measuring tweezers marketed as “Tweezers Contact Test Fixture 16334A” were used in the process. Fast determination of the entire matrix of coefficients without any special requirement for the preparation of the samples to be measured was tested and verified. The charge coefficients of the piezoelectric material were confirmed by direct methods including the laser interferometer technique, the vibrometric method, and the procedure utilizing changes of the force applied to the sample. The advantages and disadvantages of the methods were compared and defined based on measurements and their results. The main part of thesis was focused on the behavior of piezoelectric material at high temperatures near the Curie point. Depolarization performed by means of a high temperature approaching the Curie point constitutes a significant yet hardly measurable material property of PZT ceramics. Commonly available vibrometric methods (d33-meters) do not appear to be suitable for the measurement of temperature dependencies, and for that reason the frequency technique was used. The piezoelectric charge coefficient, whose value can be effectively measured via the above-discussed frequency method, was selected as the indicator showing the depolarization state in the applied piezoelectric ceramics. The accuracy of the procedure was verified via comparison of the vibrometric method in cylinders of the NCE51 ceramics with different sizes, which are designed for the longitudinal length mode. The result is an optimized measurement methodology which facilitates accurate determination of the Curie temperature, namely phase transition to the cubic crystallographic structure. The experiment also proved the applicability of progressive, controlled depolarization of PZT ceramics via high temperature, and it also enabled us to define the temperature limits at which there occur irreversible changes of the piezoelectric properties of piezoceramics. In the measured NCE51 and PCM51 materials, the limit for the irreversible changes was equal to 95% of the Curie temperature.
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Identification of changes in surface texture of the selected materials by the method of acoustic emission
Eliáš, Jan ; Bumbálek, Bohumil (referee) ; Mazal, Pavel (advisor)
This Bachelor thesis deals with monitoring changes in surface roughness of moving metal objects rubbing each other on selected parameters of acoustic emissions. Parameters of the AE signal during the movement of bronze and cast iron bodies on the surface of a fixed steel rod were measured, recorded and analyzed. These results can serve for further research on assessment possibilites of the degree of wear of a surface using the AE method. Measuring was performed using a measuring product intended for AE and the Dakel sensors and measuring software.
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Using Hilbert Huang transformation for analysis of non-stationary signals from physical experiments
Tuleja, Peter ; Balík, Miroslav (referee) ; Rášo, Ondřej (advisor)
This paper discusses the possible use of Hilbert-Huang transform to analyze the data obtained from physical experiments. Specifically for the analysis of acoustic emission in the form of acoustic shock. The introductory section explains the concept of acoustic emission and its detection process. Subsequently are discussed methods for signal analysis in time-frequency domain. Specifically, short-term Fourier transform, Wavelet transform, Hilbert transform and Hilbert-Huang transform. The final part contains the proposed method for measuring the performance and accuracy of different approaches.
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