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Measurement of Acoustic Parameters of Building Materials by Pseudorandom Sequence
Carbol, Ladislav ; Semerák,, Petr (referee) ; Koktavý, Bohumil (referee) ; Vydra,, Vítězslav (referee) ; Martinek, Jan (advisor)
The thesis deals with research of pulse compression of the acoustic signal in terms of applications in civil engineering. Based on the study and analysis of these methods, automated measuring equipment for non-destructive testing with pseudorandom sequence of maximum length and automated signal analysis, have been designed and implemented. In a single test cycle are obtained three parameters that characterize the linear and nonlinear behavior of the sample. A nonlinear parameter, Time of Flight of ultrasonic wave in the sample is further in the work compared with the conventional pulse measuring, and spectral analysis is compared with the method impact-echo. Functionality and optimization of the testing method was performed on a total of three sets of test pieces made of various building materials. The experiments proved simple result interpretation, and high sensitivity to structural damage associated with temperature loading. The results were correlated with conventional nondestructive methods and by destructive testing was measured change in compressive strength and flexural strength. This work also includes continual measurement of fundamental frequency influenced by moisture on a mortar sample. Use of pulse compression signal is in the civil engineering quite unusual. Only in recent years this topic is discussed in scientific articles with increasing frequency. Great potential lies in the association of three test methods into a single. Beneficial is high test speed and measurement reproducibility, but also theoretical possibility of testing massive test elements.
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NDT in additive manufacturing of metals
Převorovský, Zdeněk ; Krofta, Josef ; Kober, Jan
In this study we tested possibilities of nonlinear elastic wave spectroscopy (NEWS) methods to classify two types of artificially created defects in Ti-6Al-4V prismatic samples fabricated by Electron Beam Melting (EBM) system. Two series of samples with variable internal defects were tested: samples with central circular defects (missing material gaps), and samples with gradually growing stochastic porosity. Each group of samples contained also fully compact sample for a comparison. Five ultrasonic NEWS procedures were used to classify defects variability. Relatively simple experimental facility with two piezoelectric transducers allows interrogate samples and record their response. The best results, documented in this paper, were obtained by two modifications of NWMS procedure. Results of NEWS tests indicate that selected NEWS procedures can be used also for online AM monitoring.
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Measurement of Acoustic Parameters of Building Materials by Pseudorandom Sequence
Carbol, Ladislav ; Semerák,, Petr (referee) ; Koktavý, Bohumil (referee) ; Vydra,, Vítězslav (referee) ; Martinek, Jan (advisor)
The thesis deals with research of pulse compression of the acoustic signal in terms of applications in civil engineering. Based on the study and analysis of these methods, automated measuring equipment for non-destructive testing with pseudorandom sequence of maximum length and automated signal analysis, have been designed and implemented. In a single test cycle are obtained three parameters that characterize the linear and nonlinear behavior of the sample. A nonlinear parameter, Time of Flight of ultrasonic wave in the sample is further in the work compared with the conventional pulse measuring, and spectral analysis is compared with the method impact-echo. Functionality and optimization of the testing method was performed on a total of three sets of test pieces made of various building materials. The experiments proved simple result interpretation, and high sensitivity to structural damage associated with temperature loading. The results were correlated with conventional nondestructive methods and by destructive testing was measured change in compressive strength and flexural strength. This work also includes continual measurement of fundamental frequency influenced by moisture on a mortar sample. Use of pulse compression signal is in the civil engineering quite unusual. Only in recent years this topic is discussed in scientific articles with increasing frequency. Great potential lies in the association of three test methods into a single. Beneficial is high test speed and measurement reproducibility, but also theoretical possibility of testing massive test elements.
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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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Nelineární časově reversní ultrazvuková-tomografie
Převorovský, Zdeněk ; Krofta, Josef ; Převorovský, David
Nonlinear Elastic Wave Spectroscopy (NEWS) becomes new effective method for non-destructive testing of complex structures providing high sensitivity of damage detection. One of the most promising NEWS procedures is Nonlinear Time Reversal Acoustics (NLTRA) realizable in a lot of different ways. Common NLTRA procedure is mostly global, which means that localization of defect by this procedure can be often difficult. A modification of NLTRA is proposed in this paper, based on similar arrangement as ultrasonic tomography. Computer controlled switching between transmitting and receiving transducers is realized by specially designed high-voltage relay multiplexer.
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Kalibracni vzorky pro nelinearni ultrazvukovou spektroskopii
Převorovský, Zdeněk ; Van Den Abeele, K.
The experimental procedures are described, based on nonlinear elastic wave spectroscopy (NEWS). Special testing samples - PMMA blocks with laser induced cracks - are designed to verify that procedures. Opening of cracks enables kissing effect of their faces at relatively small amplitude of dynamic excitation which plays substantial role in Nonlinear Wave Modulation Spectroscopy method (frequency mixing) where it causes creation of side lobes in frequency spectra.
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