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1

The influence of AlSi10Mg recycled powder on corrosion-resistance behaviour of additively manufactured components: mechanical aspects and acoustic emission investigation

Barile Claudia, Casavola Caterina, Kannan Vimalathithan Paramsamy, Renna Gilda

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e52, 2022

EN

The effects of using recycled AlSi10Mg aluminium alloy powders on the mechanical properties and the corrosion-resistance behaviour of the components manufactured via selective laser melting (SLM) were analysed. The microstructural results show that the utilisation of recycled powder causes coarsening of interdendritic Si-network, especially along the melt pool boundaries of the SLM specimens. The corrosion resistance of the samples was evaluated by means of neutral salt spray (NSS) tests for 1000 h and mass loss measurements. The corrosion behaviour, in terms of surface roughness, density and porosity, however, remains almost the same between the samples produced by virgin and recycled powder. In addition to this, a passive NDE tool has been used to investigate and study the impact of powders on the corrosion performance of the alloy: Acoustic Emission (AE) technique. SEM observations allowed to highlight the morphological differences in the surface of the test specimens induced by the exposure condition. Thus, it was possible to correlate the AE results to corrosion mechanisms activated on the surfaces of the test specimen. A good correlation between the corrosion-resistance behaviour and the AE test results were obtained. Finally, the mechanical properties before and at the end of the accelerated corrosion were evaluated according to the yield strength, tensile strength, and elongation at breakage. The results showed comparable mechanical properties for the samples produced using both virgin and recycled powders. Besides, no notable influence of the exposure to corrosive environment on the mechanical performance was observed.

2

The Application of Acoustic Emission and Artificial Neural Networks in an Analysis of Kinetics in the Phase Transformation of Tool Steel During Austempering

Łazarska M., Woźniak T. Z., Ranachowski Z., Ranachowski P., Trafarski A.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2A

603--609

EN

During the course of the study it involved tool steel C105U was used. The steel was austempered at temperatures of 130°C, 160°C and 180°C respectively. Methods of acoustic emission (AE) were used to investigate the resulting effects associated with transformations and a large number of AE events were registered. Neural networks were applied to analyse these phenomena. In the tested signal, three groups of events were identified of: high, medium and low energy. The average spectral characteristics enabled the power of the signal spectrum to be determined. After completing the process, the results were compiled in the form of diagrams of the relationship of the AE incidence frequency as a function of time. Based on the results, it was found that in the austempering of tool steel, in the first stage of transformation midrib morphology is formed. Midrib is a twinned thin plate martensite. In the 2nd stage of transformation, the intensity of the generation of medium energy events indicates the occurrence of bainite initialised by martensite. The obtained graphic of AE characteristics of tool steel austempering allow conclusions to be drawn about the kinetics and the mechanism of this transformation.

3

Study of factors determinant of siliceous electrical porcelain resistance to structural degradation

Ranachowski P., Ranachowski Z., Kudela Jr. S., Pawełek A., Piątkowski A.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 3

1489--1496

EN

The subject of this study was investigation of the factors that have a decisive influence on the resistance of siliceous porcelain to degradation processes. There was tested material C 110 type, which is widely used for the production of low-voltage (LV) elements such as insulators and bushings. On the basis of mechanical-acoustic and microscopic research of small-sized samples, which were subjected to compression, there were distinguished successive stages of degradation of the material structure. In the authors* opinion, they have a reference to the ageing process, taking place during many years of work under operating conditions. Thus, it was possible to assess the structural factors that determine the durability and reliability of LV electroinsulating elements. The results were related to electrical aluminous porcelains.

4

Monitoring of underdeck corrosion by using acoustic emission method

Emilianowicz K.

Polish Maritime Research

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2014

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nr 1

54--61

EN

This paper presents first short characteristics of underdeck corrosion process as well as a problem of its monitoring. Next is described an acoustic emission (AE) method elaborated by Department of Ship Technology, Quality Systems and Material Engineering, Gdańsk University of Technology in cooperation with partners of CORFAT project realized within 7th EU Frame Program. Further are presented short characteristics of the emission process, used measuring instrumentation of Vallen Systeme GmbH, as well as TESTER, corrosion testing device, and a corrosion solution used in the tests. Finally, results of the tests performed on selected marine units, are presented. 1*GUT - Gdańsk University of Technology 2*TÜV- Austria 3*TESTER - a device used for simulation of corrosion processes without destruction of tested material surface. 4*Corrosive solution - a solution which catalizes corrosion processes in the tester 5*SMW S.A.- Naval Shipyard Co.

5

The Portevin –Le Chatelier Effect and Acoustic Emission of Plastic Deformation CuZn30 Monocrystals

Ozgowicz W., Grzegorczyk B., Pawełek A., Piątkowski A., Ranachowski Z.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 1

183--188

EN

The paper presents the investigation of the relation between the acoustic emission (AE) and instability of plastic deformation type Portevin-Le Chatelier (PLC) of single-phase brass CuZn30 monocrystals with crystallographical orientation [13 9]. The monocrystals have been investigated applying the method of free compression at a constant strain rate and the temperature within the range from 200°C to 400°C, simultaneously recording PLC phenomenon by means of acoustic emission. During hot axial compression tests the correlation between work-hardening curves σ - ε, which display PLC effect and characteristic of acoustic emission signals has been found. Moreover, it was proved that in the range of the PLC effect, the acoustic signal is an impulse a character of cyclic repeatability, distinctly correlated qualitatively with the stress oscillations on the curves σ - ε. The analysis of the obtained results leads to the conclusion that in the tested monocrystals the effect PLC is probably controlled by complex processes similar to the phenomenon of dynamic strain ageing (DSA), which are described by diffusion models.

PL

Streszczenie W pracy badano zależność między emisją akustyczną (EA), a niestabilnością odkształcenia plastycznego typu Portevin Le Chatelier monokryształów jednofazowego mosiądzu CuZn30 o orientacji krystalograficznej [13 9]. Monokryształy poddano próbie swobodnego ściskania przy stałej prędkości odkształcenia w zakresie temperatury od 200°C do 400°C stosując jednocześnie pomiar emisji akustycznej. Określono zależność pomiędzy przebiegiem krzywych umocnienia σ - ε wykazujących efekt PLC. a charakterystyką sygnałów emisji akustycznej generowanych w badanej próbie ściskania jednoosiowego. Stwierdzono, że w zakresie występowania efektu PLC podczas próby ściskania, sygnał EA ma charakter impulsu cyklicznego, wyraźnie skorelowany jakościowo z oscylacjami naprężeń na krzywych σ - ε. Analiza uzyskanych wyników pozwala przypuszczać, że w badanych monokryształach efekt PLC jest kontrolowany prawdopodobnie przez złożone procesy podobne do zjawisk starzenia dynamicznego po zgniocie (DSA), które są opisane modelami dyfuzyjnymi.

6

Evaluation of the mullite hypothesis in respect of electrotechnical porcelains

Ranachowski P., Rejmund F., Ranachowski Z., Pawełek A., Piątkowski A., Kudela Jr. S.

Archives of Metallurgy and Materials

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2013

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Vol. 58, iss. 4

1177--1181

EN

The paper presents the evaluation of the mullite hypothesis explaining the strength of porcelains. There was researched the influence of the mullite phase on the short- and long-term mechanical strength of electrotechnical porcelain of different types (C 110, C 112, C 120 and C 130). The total mullite phase content, the size and distribution of precipitates and dispersed single crystals in the glassy matrix were considered. Mechanoacoustic and microscopic techniques as well as ultrasonic testing were used during the investigation. The role of the mullite phase in the increase of strength and resistance to aging processes of electrical porcelain of various types was described. Mullite hypothesis is valid in reference to siliceous (C 110), cristobalite (C 112) and aluminous C 120 type materials of a typical raw components content and phase composition. In the case of modern strengthened C 120 and C 130 type aluminous materials advantageous are only dispersed fine mullite needles. The precipitates of mullite phase, especially of bigger size, are undesirable.

PL

W pracy przedstawiono ocenę teorii mulitowej wzmocnienia porcelany, w odniesieniu do tworzyw elektrotechnicznych. Przedmiotem badań był wpływ fazy mulitowej na krótko- i długotrwałą wytrzymałość mechaniczną elektroporoelan rodzaju C 110, C 112, C 120 oraz C 130. Rozpatrywana była sumaryczna zawartość fazy mulitowej. wielkość i rozłożenie jej wydzieleń oraz niezaglomeryzowanych kryształów w osnowie szklistej. W badaniach wykorzystano metodę mechanoakustyczną, techniki mikroskopowe (MO i SEM) oraz metodę ultradźwiękową. Przedstawiono rolę fazy mulitowej w podwyższeniu odporności na procesy starzeniowe porcelany elektrotechnicznej różnego rodzaju. Stwierdzono słuszność teorii mulitowej w przypadku tworzyw kwarcowych (C 110), krystobalitowych (C 112) oraz wysokoglinowych rodzaju C 120 o typowym - tradycyjnym składzie surowcowym i fazowym. W zastosowaniu do nowoczesnych, wzmocnionych tworzyw wysokoglinowych rodzaju C 120 oraz porcelan rodzaju C 130 korzystnie działają rozproszone w osnowie, niezaglomeryzowane igłowe kryształy mulitu. Wydzielenia mulitu, zwłaszcza o większych rozmiarach, są niepożądane.

7

Experimental study on fracture process of concrete by acoustic emission technology

Yang Y., Zhang L., Lv J., Wang C.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 9b

55-58

EN

Acoustic emission is a method widely used for real time monitoring of the structural condition of materials. In this paper, the uniaxial compression tests will be carried out to acquire the correlation between the characteristics of acoustic emission signals and that of the concrete strength parameter. In the fracture process of concrete, acoustic emission, which is detected by the sensors, is generated when part of the strain energy stored in the samples is rapidly released. In order to analyze the results of experiments better, the acoustic emission event rate and the strain curve are applied. The results show that the concrete strength has an important impact on acoustic emission signals: for low-strength concrete, the acoustic emission event rate columns of fracture process are divided into six stages, and display a clear "bimodal" distribution, but such phenomenon does not appear in high-strength concrete.

PL

W artykule zaprezentowano testy określające korelację między sygnałem emisji akustycznej a parametrami betonu. Badano sygnał emisji akustycznej towarzyszący pękaniu betonu.

8

Crackling noise in a discrete element model of single crack propagation

Timár G., Kun F.

Computer Methods in Materials Science

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2011

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Vol. 11, No. 2

309-314

EN

We study the crackling noise emerging during single crack propagation obtained by discrete element modelling (DEM) in a specimen under three-point bending conditions. Analyzing temporal and spatial correlations of local breakings we show that the crack proceeds in bursts, which are characterized by power law distributions of their size and of the waiting times between consecutive events. We obtain a generic scaling form which describes crackling noise in materials with different degrees of heterogeneity. The results are in a good agreement with acoustic emission measurements in three-point bending experiments.

PL

W pracy badano odgłos pękania występujący podczas propagacji pojedynczego pęknięcia w proce poddawanej trzypunktowemu zginaniu, symulowanemu za pomocą metody elementów dyskretnych (ang. Discrete element method - DEM). Analiza czasowych i przestrzennych zależności lokalnego pękania wykazała, że pęknięcie postępuje przez rozdzielenie, co charakteryzuje się prawem potęgowym opisującym rozmiar szczelin oraz czasy przerw między kolejnymi etapami pękania. Opracowano ogólną postać skalowania, które opisuje odgłos pękania w materiałach o różnym stopniu niejednorodności. Uzyskane wyniki są zgodne z pomiarami emisji akustycznej w próbie trzypunktowego zginania.

9

Mechanoacoustic and microscopic study of aluminous porcelain resistance to structural degradation

Ranachowski P., Rejmund F., Ranachowski Z., Pawełek A., Piątkowski A., Kudela S.

Archives of Metallurgy and Materials

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2011

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Vol. 56, iss. 4

1127-1233

EN

The paper presents mechanoacoustic and microscopic testing of degradation processes of modern C 120 electrotechnical porcelain of domestic medium voltage line insulator. Samples of small dimensions, cut off from the rod of insulator, were subjected to compressive loading, with recording of acoustic emission descriptors. Microscopic analysis enabled determining the advancement of degradation effects. Three stages of the structure degradation were distinguished. The effectiveness of dispersive and fibrous reinforcement of modern aluminous porcelain C 120 type has been described. Structural strengthening by corundum grains and mullite needle shaped crystals improves mechanical parameters and distinguishes this material from typical aluminosilicate ceramics. The presented results enable drawing up the conclusions concerning the resistance of investigated material to the ageing degradation process development during long term operation.

PL

W pracy przedstawiono mechanoakustyczne i mikroskopowe badania procesów degradacji w nowoczesnym tworzywie porcelanowym rodzaju C 120 liniowego izolatora SN. Małogabarytowe próbki, wycięte z pnia izolatora, były quasi-statycznie ściskane z jednoczesną rejestracją deskryptorów emisji akustycznej. Badania mikroskopowe ściskanych próbek wykorzystano do opisu mechanizmu degradacji tworzywa. Wyróżniono trzy kolejne etapy degradacji struktury tworzywa. Stwierdzono wysoką krótko- i długotrwałą odporność materiału izolatora w porównaniu do typowych tworzyw rodzaju C 120. Jest to wynikiem skutecznego dyspersyjnego i włóknistego wzmocnienia struktury czerepu badanej porcelany

10

Mechanical and acoustic emission behaviour in channel-die compressed Mg9Li alloys before and after treatment by HPT method

Pawełek A., Kudela S., Piątkowski A., Jasieński Z., Ranachowski Z., Kudela S. JR.

Inżynieria Materiałowa

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2010

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Vol. 31, nr 3

579-581

EN

The results of the investigations of acoustic emission (AE) in Mg-Li alloys of new generation: Mg9Li, Mg9Li1Al, Mg9Li3Al and Mg9Li5Al, subjected to channel-die compression tests before and after the application of intensive strain method HPT (High Pressure Torsion) are presented. The aim of these studies is the explanation of the correlations between the AE and the plastic (and possible superplastic) flow mechanisms in alloys of ultra fine-grained (nanocrystalline) structure obtained by the predeformation by HPT method. A new improved and optimized software has been used to the spectral analysis of AE signals. The earlier observations, that the microstructure refinement leads to the increase of strength and plasticity as well as the decrease of AE intensity are confirmed. The results are discussed based on the dislocation mechanisms of deformation and acoustic emission.

PL

Przedstawiono wyniki badań emisji akustycznej (EA) w stopach Mg-Li nowej generacji: Mg9Li, Mg9Li1Al oraz Mg9Li3Al i Mg9Li5Al, poddawanych próbom ściskania w matrycy kanalikowej przed i po zastosowaniu metody intensywnego odkształcania HPT (High Pressure Torsion). Celem badań było wyjaśnienie związków pomiędzy EA a mechanizmami odkształcenia plastycznego (i ewentualnie nadplastycznego) w stopach o ultradrobnoziarnistej (nanokrystalicznej) strukturze, uzyskanej dzięki przetwarzaniu metodą HPT. W badaniach zastosowano udoskonalone i zoptymalizowane oprogramowanie do analizy widmowej sygnałów EA. Potwierdzono wcześniejsze obserwacje, że rozdrobnienie mikrostruktury prowadzi do wzrostu wytrzymałości i plastyczności i wiąże się ze znaczącym spadkiem intensywności EA. Wyniki przedyskutowano, biorąc pod uwagę dyslokacyjne mechanizmy odkształcenia i EA.

11

Strength analysis of nitrided layers on austenitic stainless steel based on acoustic emission (AE) mesurements

Wojnar J.

Prace Instytutu Lotnictwa

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2009

|

Nr 5 (200)

198-204

EN

The aim of this work was to characterize deformation and failure mechanisms of layers formed during nitriding on austenitic stainless steel. The characterization was based on acoustic emission measurements performed during the static tensile test. The experimental work included the plasma nitriding process of stainless steel grade 304 samples, microhardess measurements, microstructural investigation and XRD phase analysis. The main investigation technique used was the acoustic emission measurement. The acoustic characteristics - RMS voltage, and energy, have turned out to be especially useful, as they enable to determine the real yield limit, the exact stress-strain conditions of fracture initiation at the nitrided surface and the dynamics of the fracture progress.

PL

Detonacja jest zjawiskiem, które znane jest nauce od ponad stu lat. Na ogół rozumiemy ten proces szybkiego spalania, jednak szczegóły struktury detonacji i jej mechanizm chemiczny są nadal przedmiotem intensywnych badań ze względu na ich znaczenie praktyczne. W ostatnim okresie prace badawcze nad silnikiem z wirującą detonacją (RDE) dały nowy impuls dla badań nad zjawiskiem detonacji. Z powodu geometrycznej złożoności zjawiska wirującej i obracającej się detonacji, konieczne są nowe narzędzia do badań, eksperymentalne i numeryczne. Szczególnie ważne są bardzo silne programy do symulacji silników z wirującą detonacją. Powinny one umożliwić rozwiązanie szczegółów w polu przepływu, które są niedostępne lub nawet niemożliwe do uzyskania z analizy wyników eksperymentalnych. Z drugiej strony, jeżeli zostaną one potwierdzone, mogą być one użytecznym narzędziem w przyszłości do optymalizacji silnika z wirującą detonacją. W artykule przedstawiono najnowsze próby wykorzystania takich metod, które mają umożliwić trójwymiarowe modelowanie detonacji – w ogólności, a w szczególności – modelowanie silnika z wirującą detonacją.

12

Wykorzystanie wartości skutecznej sygnału emisji akustycznej oraz metod sztucznej inteligencji do oceny zużycia ściernicy

Sutowski P.

Pomiary Automatyka Kontrola

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2009

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R. 55, nr 4

255-258

PL

W pracy przedstawiono propozycję oceny zużycia ściernic metodą pośrednią, opartą na analizie wartości skutecznej sygnału emisji akustycznej. Umiejętność podejmowania decyzji jest jednym z elementów wyróżniających inteligentne działanie, dlatego budowa systemu diagnostyki, który charakteryzowałby się takimi właściwościami wymaga użycia odpowiedniego narzędzia wykonawczego. Włączenie w układ monitorujący teorii zbiorów rozmytych, pozwoliło dokonać oszacowania stopnia stępienia czynnej powierzchni ściernicy i oceny jej okresu trwałości w trakcie procesu szlifowania.

EN

In the paper the indirect method of grinding wheel wear evaluation is presented. This method is based on analysis of the root-mean-square value of an acoustic emission signal (AE). Application of the acoustic emission signal as a measure of changes occurring in the grinding zone enables the indirect assessment of the process without its stopping. The ability to take a decision is one of the elements distinguishing intelligent activities. Design of a diagnostic system with such kind of abilities requires the use of an appropriate executive tool. The conditional attributes for an intelligent expert system were set basing on the analysis of the test results, and in particular on the grinding process output values. For individual attributes there were assumed appropriate limit values representing a sharp, average or strongly used grinding wheel not suitable for further work. As a criterion of wear there were assumed macro- and micro-changes in the active surface of the grinding wheel as well as the stress in te top layer of the workpiece. The methods of artificial intelligence were implemented in the system to ensure its correct operation. Fuzzy logic included in the monitoring system allowed estimating the degree of the grinding wheel active surface wear and its lifetime during flat surface grinding. The complete system of the grinding wheel wear control which takes into account the temporary cutting ability and the chosen quality criterion is just a conceptional solution. It is expected that this system can successfully be used for construction of monitoring units and control of machining process.

13

Materials Degradation Research on the Basis of Mechanoacoustic and Microscopic Methods

Ranachowski P., Rejmund F., Ranachowski Z., Pawełek A., Piątkowski A., Kudela S. jr.

Archives of Metallurgy and Materials

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2009

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Vol. 54, iss. 4

1035-1043

EN

The paper presents the concept of mechanoacoustic testing of degradation processes of ceramic electrotechnical materials. Samples of small dimensions are subjected to slowly increasing compressive loading with simultaneous recording of acoustic emission descriptors. The process is continued to the destruction or is stopped at various stages of degradation of the material structure. Microscopic analysis of samples enables determining the effects of stress action.

PL

W pracy została przedstawiona koncepcja mechaniczno-akustycznych badan procesów degradacji ceramicznych tworzyw elektrotechnicznych. Małogabarytowe próbki poddawane sa wolno narastajacemu obciazeniu sciskajacemu z jednoczesna rejestracja deskryptorów emisji akustycznej. Proces prowadzi sie do zniszczenia lub zatrzymuje na różnych etapach degradacji struktury. Analiza mikroskopowa próbek pozwala określić efekty oddziaływania naprężeń.

14

Test stand in university of applied science giessen for friction forces measurements in slide bearing using the acoustic emission method

Ziegler B., Wierzcholski K., Miszczak A.

Journal of KONES

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2008

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Vol. 15, No. 3

591-595

EN

The present paper shows particularly description of the construction of the test stand for experimental research performed in University of Applied Science Giessen and connected with the measurements of hydrodynamic friction forces in journal slide bearings by using the Acoustic Emission Method. The test stand is adapted for the friction force measurements for the low bearing load and for the high bearing load. For such test stand in the case of low and high loads the dependencies between friction forces and time can be exactly obtained. During the measurements the temperature changes are expected. The advantage of this method is the fact that oscillations of measured friction values can be executed directly from the source to the sensor, what enables us to do an "online-measurement". The Acoustic Emission Analysis is (in opposite to the aforementioned Friction Power measurement) a relative method, which means, that the absolute amount of a RMS-Value depends on the measuring chain.

15

Friction forces measurements for slide bearing test stand in maritime university Gdynia using the acoustic emission method

Ziegler B., Wierzcholski K., Miszczak A.

Journal of KONES

|

2008

|

Vol. 15, No. 2

571-577

EN

The present paper determines the results of experimental research performed in Gdynia Maritime University and connected with the measurements of hydrodynamic friction forces in slide journal slide bearings by using the Acoustic Emission Method. A new method for mechanical friction force measuring was carried out at this test stand, simultaneously the friction force will be indicated by an optimized Acoustic Emission System. The friction conditions at the test were measured by two different methods. At the one hand the friction power measurement and at the other hand the Acoustic Emission Analysis. One characteristic of the friction power measurement is the rather inert reaction to the oscillations of the slide bearing. The advantage of the method is the fact that one can measure absolute values of the friction power. In opposite to that, the Acoustic Emission Analysis measures the high frequency oscillations caused by the hydrodynamic friction between the oil molecules. The advantage of this method is the fact that this oscillations can be executed directly from the source to the sensor, what enables us to do an "online-measurement". The Acoustic Emission Analysis is (in opposite to the aforementioned friction power measurement) a relative method, which means, that the absolute amount of a RMS-Value depends on the measuring chain. The results are compared and discussed with other results obtained in experiments performed in University of Applied Science Giessen.

16

Friction forces measurements by the acoustic emission for slide bearing test stand in uni of applied science Giessen

Ziegler B., Wierzcholski K., Miszczak A.

Journal of KONES

|

2008

|

Vol. 15, No. 4

627-633

EN

The present paper describes the results of measurements performed in University of Applied Science Giessen and determined hydrodynamic friction forces in journal slide bearings by using the Acoustic Emission Method. It describes the use of the Acoustic Emission Analysis as an indicator of the bearing friction at slide bearings. The investigations were made at two different test stands. The test stand at Maritime University Gdynia covers the hydrodynamic operation range, the test stand at University of Applied Science Giessen the mixed friction area. The successive steps of measurements of the hydrodynamic friction forces are presented in this paper. Hardness and roughness of cooperating surfaces is in this paper particularly described. The friction values and its boundary conditions at the test were measured for the low bearing load and for the high bearing load. In both cases, the dependencies between friction forces and time are exactly obtained. During the measurements, the temperature is taken into account. The advantage of this method is the fact that these oscillations can be executed directly from the source to the sensor, what enables us to do an "online-measurement". The Acoustic Emission Analysis is (in opposite to the aforementioned friction power measurement) a relative method, which means, that the absolute amount of a RMS-Value depends on the measuring chain. The results are compared and discussed with other results obtained in experiments performed in Maritime University Gdynia.

17

Application of signal processing elements for the characteristics of acoustic emission pulses generated by partial discharges

Boczar T., Borucki S., Cichoń A., Lorenc M.

Molecular and Quantum Acoustics

|

2007

|

Vol. 28

23-38

EN

The subject matter of this paper refers to the issues connected with the application of modern numerical methods in processing and analysis of the signals measured by the acoustic emission method (AE) during high-power experiments carried out in laboratory conditions in the setups modelling basic partial discharge forms (PDs). The detailed cognitive aim of the research work was determining the possibilities and the application range of the short time Fourier transform (STFT) and wavelet transform in the analysis of the AE pulses generated by basic PD forms that can occur in oil insulation systems of such appliances as transformers, measuring transformers, bushing insulators, switchgears, and power condensers. The time – frequency analysis was carried out for the particular PDs from the point of view of determining differences and indicating common features for the frequency structures determined, for the positive and negative voltage polarizations separately. The research concentrated mainly on the following types of PDs: point-plane, multipoint-plane, multipoint-plane with a layer of pressboard, surface, generated in gas bubbles and on the indeterminate-potential particles moving in oil. In calculations using wavelet transformations basic types of analyzing functions, the so-called basic wavelets, were applied. When determining amplitude spectrograms of the AE pulses measured various types of observation windows were used. Moreover, for the approximation runs determined and for the particular details the autocorrelation functions (ACF) were calculated, and the probability density functions (PDF) were calculated to determine statistical properties. Also, frequency spectrum runs for the AE pulses measured and the diagrams corresponding with the details analyzed, which visualize the size of energy transferred at the particular decomposition levels, were determined. The paper presents the results of measurements and analyses of the AE pulses generated by the PDs in oil in the multipoint-plane with a layer of pressboard system.

18

Acoustic emission and the Portevin-Le Châtelier effect in tensile tested Al alloys processed by ARB technique

Pawełek A., Kuśnierz J., Bogucka J., Jasieński Z., Ranachowski Z., Ranachowski P., Rejmund F., Dębowski T.

Archives of Acoustics

|

2007

|

Vol. 32, No. 4

955--962

EN

The paper presents the investigations of the relation between the acoustic emission (AE) and the Portevin-Le Châtelier (PL) phenomena occurring in tensile tested two kinds of aluminium alloys: not-predeformed and predeformed earlier using the technique of accumulative rolling banding (ARB). There have been found essential correlations between AE and PL effects in ARB not-predeformed alloys. The tensile tests for ARB predeformed alloys were performed on a series of samples of various degree of work hardening and it has been observed that the correlations between the AE and PL effects are not so pronounced as in the case of ARB not-predeformed alloys. The results of AE measurements obtained using a new software allowed additionally to carry out the spectral analysis of AE signals and, in consequence, to determine the acoustic maps (acoustograms) and the spectral characteristics which are very useful in the discussion of the relations between the non-homogeneous strain mechanisms of the PL effect and the mechanisms of AE events generation. The results are discussed in the context of the existing dislocation models of the PL effect and the theoretical concepts of AE sources.

19

Determination of structural and thermal-physics requirements of stabilization of an equilibrium crystallization of a eutectic alloys

Prokhorenko S., Stadnyk B., Bylica A.

Archiwum Odlewnictwa

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2002

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R. 2, nr 6

189-194

EN

Some considerations that have been prepared by the authors as a preliminary basis for creation of the national temperature reference points using metal alloys of eutectic concentration as a working element are presented. The substantiation of the possibility of eutectics application done with the account of modern achievements of physics of metals is given. For addilional control of melting / crystallization cycles parameters invariance the Procedure of Spectrum Comparison of the parameters of Acoustic Emission from the alloy is suggested to be used.

PL

W artykule podano uzasadnienie z pozycji ostatnich osiągnięć fizyki metali ciekłych możliwości wykorzystania eutektyk w jakości dodatkowych punktów odniesienia skali temperaturowej ITS-90. Jako metodę uzupełniającej kontroli zaproponowano użyć metodę porównywania parametrów spektrów Emisji Akustycznej, szczególnie parametru katastroficzności Kp.