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Hodnocení kvality pomocí nedestruktivních technologií
Ševčík, Michal
The diploma thesis titled "Quality assessment by non-destructive technologies" is focused at evaluation degradation qualities of welded components, which are material heterogeneous. Welded samples are made for experimental measuring by CMT method and their degradation qualities are measured by the acoustic emission during the corrosion process and tensile straining. The theoretical part is aimed at on basic division most used method NDT, the main stress is on AE. Te final part is focused on corrosion engineering, especially on problematic galvanic corrosion, which is important in case of interaction of homogenous materials. Material samples which were used are mentioned at the beginning of experimental part. Then the thesis is dedicated to summary of methods used during the measurement. The next chapter provides courses and exp. results of observations and measurements using AE. Courses and exp. results of observations and measurements using AE are in the last chapter.
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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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Correlation of AE Signal Changes to Rolling Contact Damage Propagation
Nohál, Libor ; Čermák, Jan (referee) ; Hájek, Karel (referee) ; Hutař, Pavel (referee) ; Mazal, Pavel (advisor)
This PhD thesis deals with the experimental study of more precise rolling contact fatigue damage detection using acoustic emission method. A series of experiments was carried out on two representatives bearing steels and the analysis of sensitivity for the presence of contact damage was performed on selected parameters of acoustic emission. The extent of damage was classified into four classes and signal parameters the most characterizing the development of damage were correlated with the extent of damage. It was also verified the influence of lubricants on acoustic emission signals. The results have an impact on the implementation of more precise rolling contact fatigue tests and evaluation of parameters of acoustic emission signal. On the basis of experiments was established methodology for more precise RCF testing method using acoustic emission on test-rig AXMAT II.
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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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Evaluation of Cyclic Damage in Aluminum and Magnesium Alloys Using Acoustic Emission Technique
Vlašic, František ; Mazal, Pavel (advisor)
The thesis deals with the application of nondestructive testing methods (acoustic emission, electron microscopy, X-ray diffraction topography) to description and identification of stages in the fatigue process in aluminium alloys. The main contribution of this dissertation thesis consists of the approach and evaluation methodology of cyclic damage in the materials. It dealt especially with the verification of measured data by using data obtained using other nondestructive methods. The experimental results show that the field of nondestructive testing materials can fundamentally uncover the process of fatigue damage and improve current knowledge in this area. Combination of used methods has become a powerful tool for the identification and monitoring of the whole fatigue degradation process of materials.
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Evaluation of Cyclic Damage in Aluminum and Magnesium Alloys Using Acoustic Emission Technique
Vlašic, František ; Samek,, Jiří (referee) ; Fiala, Jaroslav (referee) ; Pazdera, Luboš (referee) ; Mazal, Pavel (advisor)
The thesis deals with the application of nondestructive testing methods (acoustic emission, electron microscopy, X-ray diffraction topography) to description and identification of stages in the fatigue process in aluminium alloys. The main contribution of this dissertation thesis consists of the approach and evaluation methodology of cyclic damage in the materials. It dealt especially with the verification of measured data by using data obtained using other nondestructive methods. The experimental results show that the field of nondestructive testing materials can fundamentally uncover the process of fatigue damage and improve current knowledge in this area. Combination of used methods has become a powerful tool for the identification and monitoring of the whole fatigue degradation process of materials.
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APPLICATION OF ACOUSTIC EMISSION METHOD FOR MORE DETAILED DIAGNOSTICS OF RADIAL BEARINGS DAMAGE
Hort, Filip ; Pazdera, Luboš (referee) ; Hájek, Karel (referee) ; Samek,, Jiří (referee) ; Mazal, Pavel (advisor)
This thesis studies the possibilities of exploiting the acoustic emission method as a tool for more detailed identification of the radial bearings damage formation. The work includes comparison of different evaluation methods in laboratory tests. Applied couplant between the contact sensor areas and sensing surfaces is also taken into account. The practical part includes the presentation of the experimental station and structural adjustments made. The main part of the work comprises the examples in detail of three types of experimental tests that simulate the possible failure of bearings and their manifestation in the sensing signal. Testing methodology developed with recommended values for setting common AE signal measurement, vibration and temperature is a part of the thesis, too.
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Application of Electromagnetic and Acoustic Emission for the Diagnostics of Advanced Composite Materials
Trčka, Tomáš ; Chobola, Zdeněk (referee) ; Lokajíček,, Tomáš (referee) ; Koktavý, Pavel (advisor)
The subject of this dissertation is a theoretical and experimental study of electromagnetic and acoustic emission generated in the course of crack formation in solid dielectric materials. Theoretical part of this work is focused on the electromagnetic emission method, because it is related to a number of unsolved problems in the field of generated emission signals measurement, as well as in the field of the correct interpretation of obtained experimental data. Consequently, issues of emission signals detection by capacitance sensors and the transformation of crack primary parameters on the measured variables within the proposed transfer system have been dealt with. The results in this area were an extension of application range of the electromagnetic emission method on composite materials (especially on fiber reinforced polymer composites), identification and evaluation of the most significant emission sources in investigated composites and developing a methodology for evaluating of the crack primary parameters based on the measured emission signals waveforms in time and frequency domain. The experimental part of this dissertation was focused on a complex methodology for emission signals (including data from additional sensors) continual recording, processing and evaluation and for monitoring the response of stressed material to an applied mechanical load in real-time. Partial results from different research areas were also implemented into this methodology. This included the detection of emission signals, design and implementation of the appropriate measuring apparatus, analysis of measured signals in the time and frequency domain and advanced methods for processing and evaluation of measured data.
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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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