Instytut Podstawowych Problemów Techniki

Streszczenie:

The paper presents the modeling of transmission of the ultrasonic plane wave through an uniform liquid layer. The considered sources of the ultrasonic wave were normal (straight) beam longitudinal wave probes and angle beam sheer waves probes commonly used in non-destructive testing. Coupling losses (CL) introduced by the presence of the coupling layer are discussed and determined applying the numerical procedure. The modeling applies to both monochromatic waves and short ultrasonic pulses with a specified frequency bandwidth. Model implementation and validation was performed using a specialized software. The predictions of the model were confirmed by coupling losses measurements for a normal beam longitudinal wave probe with a delay line made of polymethyl methacrylate (PMMA). The developed model can be useful in designing ultrasonic probes for high-speed rail track inspections, especially for establishing the optimal thickness of the water coupling layer and estimation of coupling losses, due to inevitable changes of the water gap during mobile rail inspection.

Słowa kluczowe:

non-destructive testing, ultrasonic examination, plane wave propagation

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W pracy przedstawiono wyniki badań próbek tekstolitowych elementów osłonowo-centrujących z eksploatowanych ograniczników przepięć SN. Prądy wyładowcze (zwarciowe) o zróżnicowanym natężeniu i czasie trwania spowodowały w tworzywie elementów efekty degradacji o różnym stopniu zaawansowania, które badano z wykorzystaniem metod mikroskopowych i mikroanalizy rentgenowskiej EDS. Udokumentowano zmiany w składzie elementarnym (zawartości pierwiastków) warstwy wierzchniej tworzyw tekstolitowych - w miarę postępu efektów degradacji. Wykazano, że tworzywa te posiadają niewystarczającą odporność na skutki awaryjnej pracy ogranicznika przy jego zawilgoceniu, które jest konsekwencją rozszczelnienia osłony.

Słowa kluczowe:

ogranicznik przepięć, tekstolit szklany TSE, prąd wyładowczy (zwarciowy), metoda EDS

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Material Aspects of Historic Fine Ceramics The paper outlines the material and technological aspects of fine (whiteware) ceramics. Particular attention has been paid to the professional nomenclature of fine aluminosilicate ceramics as used in the past and today. Attention was drawn to this mostly overlooked and poorly studied problem. The reason for the durability problems of some semi-vitreous porcelain and faience materials has been explained. The microstructures of porcelain materials – historic as well as contemporary – have been presented in comparative terms, including the technical material, with a distinction and analysis of the basic phases that build up the shard. Generally similar parameters of microstructure and phase composition were found for all tested materials.

Słowa kluczowe:

historic faience, semi-vitreous porcelain, historic porcelain, microscopic analysis, microstructure of ceramic shard

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The paper presents an investigation of the railhead steel R260. Brinell hardness was measured, spherical microindentation tests were performed and the microstructure was analysed using optical microscopy and SEM images. Fatigue damage in various near-surface regions of the railhead was estimated on the basis of local deterioration of elastic modulus and the development of plastic work in cyclic microindentation tests. There is a clear difference in hardness and fatigue damage between the used and the virgin regions of the railhead. The Brinell hardness and ultrasonic measurements show a change in material properties due to rail manufacturing process.

Słowa kluczowe:

Fatigue damage, Microindentation, Brinell hardness, Ultrasonic measurements, Railhead

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The aim of this work was to investigate the effects of the currents flowing through surge arresters on the internal insulating textolite structure. The samples were removed from high-voltage arresters that were taken out of service due to malfunction or failure. Discharge (short-circuit) currents of diverse intensities and durations caused degradation effects of varying degrees of advancement in the material of the tested elements. The samples were examined using microscopic methods. The use of the microanalysis technique EDS (energy-dispersive X-ray spectroscopy) made it possible to register changes in the elemental composition of the surface layer of the textolite materials, along with the intensification of the degradation effects. It was found that the high discharge current flows were subject to melting, charring and even burning of the organic adhesive. These effects caused serious changes in the content of elements in the top layer of the textolite and were the cause of a reduction in the service life, durability and reliability of the surge arresters. It was shown that the textolite materials had insufficient resistance to the effects of the emergency operation of the arresters after moisture ingress, which was a consequence of unsealing of the housing. A solution to this problem proposed by the authors could be the use of silicone elastomer as a covering of the textolite internal structure of surge arresters.

Słowa kluczowe:

surge arrester, TSE glass textolite, discharge (short circuit) current, EDS method

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The article presents the application of Acoustic Emission (AE) method for detection and registration of partial discharges (PD) generated in medium voltage (MV) cable isolation and MV cable head. The insulation of the high voltage cable is made of a flexible material whose properties are characterised by a high coefficient of attenuation of the acoustic signals. For this reason, the AE method has not been used so far to detect PD in energetic cables. The subjects of the research were the MV cable and the standard T-type cable head. The cable contained defects which were the source of partial discharges. In case of cable head the PD were provoked by thin grounded electrode which was introduced into connector opening. The results of AE measurements are presented in the form of spectrograms. Acoustic Emission was evoked when the applied voltage level reached the value of 7.5 kV for the cable and 4 kV for the cable head. The authors used the acoustic instrumentation of their own design intended for future field use. Obtaining successful results of partial discharges measurements using the acoustic method in the cable insulation makes an original contribution of the presented work.

Słowa kluczowe:

partial discharges, medium voltage insulation, acoustic emission

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The goal of the research was to analyze the acoustic emission signal recorded during the heat treatment. On a special stand, samples prepared from 27MnCrB52 steel were tested. The steel samples were heated to 950°C and then cooled continuously in the air. Signals from phase changes occurring during cooling were recorded using the system for registering Acoustic Emission. As a result of the changes, Widmanstätten ferrite and bainite structures were observed under the scanning microscope. The recorded Acoustic Emission signal was analyzed and the signal was assigned to the appropriate phase transformation with the use of artificial neural networks.

Słowa kluczowe:

microstructure, phase transformation, ultrasonics, acustic emision, continuous cooling

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Acoustic emission and dilatometry were applied to investigate the characteristics of phase transformations in bearing steel 100CrMnSi6-4 during austempering below the martensite start temperature (MS 175 °C) at 150 °C. The aim of this study is to characterize the product of transformation occurring below the MS temperature using various research methods. Analysis of the dilatometric curves shows that, after the formation of athermal martensite below the MS temperature, the austenite continues to undergo isothermal transformation, indicating the formation of bainite. Additionally, tests were carried out with the use of acoustic emission during isothermal hardening of the adopted steel. The obtained acoustic emission signals were analyzed using an artificial neural network. The results, in the form of a graph of the frequency of acoustic emission (AE) event occurrence as a function of time, make it possible to infer about the bainite isothermal transformation. The results of this research may be used in the future to design optimal heat treatment methods and, consequently, may enable desired microstructure shaping.

Słowa kluczowe:

bainite, austempering, acoustic emission, neural networks, dilatometry

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In this article, we presented the results of the tests performed on three sets of samples of glass-reinforced epoxy (GRE) core rods used in alternating current (AC) composite insulators with silicone rubber housing. The objective of this examination was to test the aging resistance of the rod material when exposed to direct current (DC) high voltage. We hypothesized that the long-term effects of the electrostatic field on the GRE core rod material would lead to a gradual degradation of its mechanical properties caused by ionic current flow. Further, we hypothesized that reducing the mechanical strength of the GRE core rod would lead to the breakage of the insulator. The first group of samples was used for reference. The samples from the second group were subjected to a temperature of about 50 °C for 6000 h. The third group of samples were aged by temperature and DC high voltage for the same time. The samples were examined using the 3-point bending test, micro-hardness measurement and microscopic analysis. No recordable degradation effects were found. Long-term temperature impact and, above all, the combined action of temperature and DC high voltage did not reduce the mechanical parameters or change the microstructure of the GRE material.

Słowa kluczowe:

DC high voltage, composite insulator, glass-reinforced epoxy core, 3-point bending test, mechanical strength, micro-hardness

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In the paper the calculation of ultrasonic field generated by the transmitting transducer and the energy of the beam returning after the reflection at the defect in the rail volume is presented. The focus of the authors is directed on the specific transducer - defect configurations where the common methods of determination of ultrasonic beam trajectory fails. To solve this problem the refraction effexts are studied and its impact is calculated.

Słowa kluczowe:

non-destructive testing, rolling contact fatigue damage, ultrasound

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The aim of this study was to investigate the effect of plasterboards' humidity absorption on their performance. Specimens' hydration procedure consisted of consecutive immersing in water and subsequent drying at room temperature. Such a procedure was performed to increase the content of moisture within the material volume. The microstructural observations of five different plasterboard types were performed through optical and scanning electron microscopy. The deterioration of their properties was evaluated by using a three-point bending test and a subsequent ultrasonic (ultrasound testing (UT)) longitudinal wave velocity measurement. Depending on the material porosity, a loss of UT wave velocity from 6% to 35% and a considerable decrease in material strength from 70% to 80% were observed. Four types of approximated formulae were proposed to describe the dependence of UT wave velocity on board moisture content. It was found that the proposed UT method could be successfully used for the on-site monitoring of plasterboards' hydration processes.

Słowa kluczowe:

plasterboards, moisture content, hydration processes, mechanical properties, ultrasound measurements

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The paper presents results of investigation of microstructure and micro-hardness for material of ZnO varistors applied to 110 kV surge arrester and surge arrester counter. The research combined two pairs of varistors, each consisted of one varistor subjected before to operation, while the other one was brand new unit and constituted a reference. All varistors were made of the same material by the reputable manufacture. The tests revealed a different degree of the material degradation for varistors subjected before to operation. This also refers to different degradation mechanism observed for the material of these varistors, if typical effects of degradation of aged ZnO varistors were considered as a reference. Physical state of spinel in the microstructure had a significant impact on the material degradation, however a considerable loosening of the microstructure associated with bismuth oxide was observed too. It was surprising, since the precipitates of the bismuth oxide phase most often showed very good binding to the ZnO matrix and high resistance to associated electrical, thermal and mechanical effects. The degradation effects in the ZnO matrix proved to be limited only.

Słowa kluczowe:

surge arrester, surge arrester counter, MO varistors, microstructure of ceramics, ceramic material degradation

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Two types of composites, consisting of pure magnesium matrix reinforced with two commercially used carbon fibers, were systematically studied in this paper. The composites fabricated by the pressure infiltration method, were subjected to quasistatic and dynamic compression tests. Morphology of fiber strands was observed using scanning electron microscope (SEM). The application of carbon fibre reinforcement led to the stiffening of tested materials, resulting in the limitation of the possible compression to approx. 2.5%. The performed tests revealed the remarkable difference in compression strength of investigated compositions. The cause of that effect was that GRANOC fiber reinforced composite exhibited insufficient bond quality between the brittle fibers and the ductile matrix. T300 reinforced composite presented good connection between reinforcement and matrix resulting in increased mechanical properties. Investigated composites demonstrated higher mechanical strength during deformation at high strain rates. Microscopic observations also proved that the latter fibers with regular shape and dense packaging within the filaments are proper reinforcement when designing the lightweight composite material.

Słowa kluczowe:

Mg matrix composite, compressive properties, carbon fiber, Split-Hopkinson pressure bar

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Celem prezentowanej pracy było znalezienie zależności pomiędzy parametrami mikrostruktury warystorów, a prądem płynącym przez ogranicznik przepięć dla różnych poziomów napięcia. Badania zostały wykonane na losowo wybranej populacji beziskiernikowych ograniczników przepięć w osłonach polimerowych, przeznaczonych do pracy w sieci średniego napięcia. Wykonano pomiary przebiegów referencyjnych dla badanej populacji ograniczników. Przyjęto jako kryterium oceny udział wyższych harmonicznych w przebiegu prądu. Praca stanowi wstęp do szerszego zakresu badań, prowadzonych w ramach wspólnych działań laboratoriów Instytutu Energetyki i Instytutu Podstawowych Problemów Techniki PAN.

Słowa kluczowe:

beziskiernikowy ogranicznik przepięć, warystor ZnO, mikrostruktura ceramiki, analiza FFT

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Composite materials based on MgLi and MgY matrices reinforced with unidirectional T300 carbon fibres (45 vol.%) have been prepared by gas pressure infiltration technique. Nominal Li and Y alloying of Mg matrix were 0.5, 2, and 4 wt.% Li and 7, 13, and 20 wt.% Y, respectively. Back-scattered electron (BSE) observations and electron dispersive X-ray (EDX) analysis have revealed that penetration of lithium and formation of lithium carbide Li2C2 inside carbon fibres took place. Bending tests have shown that low Li alloying of Mg matrix (0.5 and 2 wt.% Li) has a favourable effect on the strength of MgLi/T300 composites. Higher Li content (4 wt.% Li) brings a much lower composite strengthening presumably due to degradation of carbon fibres with Li2C2. A negative effect of high yttrium alloying on the strength of MgY/T300 composites is explained by poor adherence of YC2 interfacial layer to carbon fibres.

Słowa kluczowe:

magnesium matrix, magnesium composites, magnesium-lithium matrix, magnesium-lithium composites, magnesium-yttrium matrix, magnesium-yttrium composites, lithium carbide, yttrium carbide, reactive wetting

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The aim of the present study was to investigate the degradation of the microstructure and mechanical properties of fiber cement board (FCB), which was exposed to environmental hazards, resulting in thermal impact on the microstructure of the board. The process of structural degradation was conducted under laboratory conditions by storing the FCB specimens in a dry, electric oven for 3 h at a temperature of 230 °C. Five sets of specimens, that differed in cement and fiber content, were tested. Due to the applied heating procedure, the process of carbonization and resulting embrittlement of the fibers was observed. The fiber reinforcement morphology and the mechanical properties of the investigated compositions were identified both before, and after, their carbonization. Visual light and scanning electron microscopy, X-ray micro tomography, flexural strength, and work of flexural test Wf measurements were used. A dedicated instrumentation set was prepared to determine the ultrasound testing (UT) longitudinal wave velocity cL in all tested sets of specimens. The UT wave velocity cL loss was observed in all cases of thermal treatment; however, that loss varied from 2% to 20%, depending on the FCB composition. The results obtained suggest a possible application of the UT method for an on-site assessment of the degradation processes occurring in fiber cement boards.

Słowa kluczowe:

cement-based composites, fiber cement boards, durability, ultrasound measurements

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The paper presents the results of the study of the influence of the addition of retarding superplasticising admixture based on triisobutyl phosphate and modified phosphonates on the amount of heat generated by hardening shielding concrete. A four-point measurement of the heat generated during the hardening of concrete with an admixture dose of 0, 0.5, 1.0 and 2.0% by weight of the cement was made and the concurrent measurement of the heat released by the hardening cement paste was measured with an isothermal calorimeter. Based on the results from the calorimeter, the effect of the admixture on the temperature field in the hardening concrete mass elements was simulated for different aggregates. The results indicate that the admixture clearly lowers the temperature gradient in hardening mass concrete. In the simulations, the most clear effect was achieved in the case of concrete with barite aggregate, where the gradient value was reduced from 10°C/m to 8°C/m for an admixture content equal to 2.0%.

Słowa kluczowe:

temperature gradient, heat release, shielding concrete, mass concrete, fresh concrete, phosphorus compounds

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The paper presents investigations of microstructure of varistors of damaged surge arrester counters. A similar ZnO varistor, not subjected before to operation, was a point of reference in this research. The results of investigations of the ZnO varistors show an untypical phase composition of their material, which was characterized by unsatisfying homogeneity and cohesion. The degradation processes of varistor material in the subsequent stages were recognized and described. A harmful impact of humidity inside the untight surge arrester counter on its operation and its ZnO varistors was proved. Some conclusions being the result of the operation checking of surge arrester counters were presented too.

Słowa kluczowe:

surge arrester counter, ZnO varistors, microstructure of ceramics, ceramic material degradation

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The paper presents the test results for the microstructure of ZnO varistors comprising high voltage gapless surge arresters. The tests were performed on varistors produced in different periods and by various manufacturers. The research was inspired by different characteristics of changes in values of current flowing through surge arresters as a function of changes in values of system voltage in a 220 kV substation, and the temperature in a multi-year cycle. Furthermore, the effects of varistor microstructure degradation following a failure of an unsealed surge arrester were investigated. The results provided the grounds for assessment of ZnO varistor microstructure parameters in terms of their durability and resistance to degradation processes.

Słowa kluczowe:

surge arrester, MO varistor, microstructure of ceramics, ceramic material degradation

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The paper presents the microscopic and mechanoacoustic study of degradation processes of the porcelain material C 130 type. This kind of material is used in the production of the most durable and reliable electrotechnical elements. Raw material composition of the studied porcelain was modified. This had an impact on the inner properties, cohesion and – in consequence – on operational properties of the material. Using mechanical-acoustic and microscopic methods of testing of small-size samples that were subjected to compression, it was possible to distinguish successive stages of degradation of the porcelain structure. These stages were generally typical of the porcelain materials. In the authors’ opinion, they are connected to the ageing process happening over many years of work under operating conditions. Optimization of composition and technological properties – important during technological processes – resulted in a slight decrease in inner cohesion of the porcelain. When compared to the reference material – typical domestic C 130 material, mechanical strength was somewhat lower. Carried out investigations proved that resistance of the investigated material to the ageing degradation process – during long term operation – also decreased. The improvement of technological parameters and the reduction in the number of defective elements occurred simultaneously with some decrease in the operational parameters of the material. To restore their initial high level, further work is needed to optimize the raw material composition of the porcelain.

Słowa kluczowe:

electrical porcelain materials, ageing processes, acoustic emission (AE), optical microscopy

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This article presents the results of an examination performed on a set of samples of glass-epoxy core rods used in composite insulators with silicone rubber housings. The goal of the examination was to test the aging resistance of the core material when exposed to Direct Current (DC) high voltage. Long term exposure of a glass-epoxy core rod to DC high voltage may lead to the gradual degradation of its mechanical properties due to the ion migrations. Electrolysis of the core material (glass fiber) may cause electrical breakdown of the insulators and consequently lead to a major failure. After being aged for 6000 hours under DC high voltage, the samples were subjected to microscopic analysis. Their chemical composition was also examined using Raman spectroscopy and their dielectric losses and conductance in the broad range of frequencies were tested using dielectric spectroscopy.

Słowa kluczowe:

DC high voltage, composite insulator, glass-epoxy core, dielectric spectroscopy, Raman spectroscopy

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The microscopic analysis of the different cellulose fibre cement composites is presented. The observations of the fibres in optical microscope in transmitted light and in scanning electron microscope are described. The micro computed tomography (micro-CT) and SEM were used to determine the distribution of the fibres in the matrix. The investigated fibre cement boards were produced by extrusion process and panels were cured in natural conditions. The main goal of the research was application of different microscopic methods to analyze the fibres distribution as a result of a different methods of their production. Micro-CT was used for 3D visualization of fibres distribution in three different fibre cement boards. It was possible to determine the average diameter of the fibres and their concentration using the high-resolution mode of micro-CT scanning procedure. Finally, a procedure which can be applied as a useful tool for analysis of the different procedures used in production of fibre cement boards is described. This procedure can be successfully used in the quality control system of cellulose fibre distribution in cement composites

Słowa kluczowe:

Cellulose fibre reinforced cement boards, Microstructure, Fibre distribution, X-ray microtomography, SEM-EDS analysis

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W pracy przedstawione zostały doświadczenia z eksploatacji liczników zadziałań, które stanowiły inspirację do badań pochodzących z nich warystorów ZnO. Badana była mikrostruktura elementów pochodzących z uszkodzonych liczników zadziałań. Odniesienie stanowił analogiczny warystor, z licznika który nie był w eksploatacji. Badania wykazały nietypowy skład fazowy tworzywa badanych warystorów oraz niską jednorodność i spoistość ich czerepu. Opisano i udokumentowano procesy degradacji tworzywa o zróżnicowanym nasileniu. Wykazano szkodliwy wpływ wilgoci we wnętrzu rozszczelnionego licznika zadziałań na jego funkcjonowanie, w tym na umieszczone w nim warystory ZnO. Przedstawiono ponadto wnioski dotyczące kontroli eksploatacyjnej liczników zadziałań.

Słowa kluczowe:

licznik zadziałań, warystory ZnO, mikrostruktura ceramiki ZnO, degradacja materiału ceramicznego

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Fiber cement boards (FCB) microstructure and methods of fabrication are described. The method of X-ray microtomography in application for investigating of FCB microstructure is presented. The cellulose fibers constituting the remarkable reinforcement of the FCB are colorless and too small to be seen applying the standard optical methods. The X-ray microtomography method however enabled the authors to realize three goals within the investigation of the properties of FCB. The length and shape of the fibers could be assessed on specimens' cross-sections. Applying the pseudo 3D visualization it was possible to visualize the cracked regions inside the specimen volume. The case of non-uniform fibers distribution in respect to the board thickness which was impossible to recognize applying the standard visual inspection, was also performed by merging the multiple cross-section images into a single graph

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The paper concerns the role of cellulose reinforcements in overall mechanical toughness of fiber concrete panels applied as facade building material. The results of mechanical tests performed on specimens in as delivered state as well as on specimens which underwent the procedure of destruction of internal fiber network structure due to pyrolysis are presented. The results of mechanical tests let the authors to calculate the work of fracture for six different mechanical conditions. Moreover the analysis of registered Acoustic Emission (AE) signal had revealed that the investigated process of destruction begins with the brittle crack generation and growth while major damages of reinforcement system appears in later phase of the process.

Słowa kluczowe:

Fiber cement panels, Cellulose fibers, Brittle crack, Acoustic Emission

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Bearing steel 100CrMnSi6-4 and tool steel C105U were used to carry out this research with the steels being austempered to obtain a martensitic-bainitic structure. During the process quite a large number of acoustic emissions (AE) were observed. These signals were then analysed using neural networks resulting in the identification of three groups of events of: high, medium and low energy and in addition their spectral characteristics were plotted. The results were presented in the form of diagrams of AE incidence as a function of time. It was demonstrated that complex transformations of austenite into martensite and bainite occurred when austempering bearing steel at 160 °C and tool steel at 130 °C respectively. The selected temperatures of isothermal quenching of the tested steels were within the area near to MS temperature, which affected the complex course of phase transition. The high activity of AE is a typical occurrence for martensitic transformation and this is the transformation mechanism that induces the generation of AE signals of higher energy in the first stage of transition. In the second stage of transformation, the initially nucleated martensite accelerates the occurrence of the next bainitic transformation.

Słowa kluczowe:

microstructure, phase transformation, dislocation, ultrasonics, alloys

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Two different barite ore (barium sulfate BaSO4) specimens from different localizations were tested and described in this paper. Analysis of the microstructure was performed on polished sections, and on thin sections using X-ray microtomography (micro-CT), and optical microscopy (MO). Microtomography allowed obtaining three-dimensional images of the barite aggregate specimens. In the tomograms, the spatial distribution of the other polluting phases, empty space as well as cracks, pores, and voids – that exceeded ten micrometers of diameter-were possible to visualize. Also, the micro-CT allowed distinguishing between minerals of different density, like SiO2 and BaSO4. Images obtained and analyzed on thin sections with various methods using the optical microscopy in transmitted light delivered additional information on the aggregate microstructure, i.e. allow for estimation of the different kinds of inclusions (like the different density of the minerals) in the investigated specimens. Above methods, which were used in the tests, completed each another in order to supply a set of information on inclusions' distribution and to present the important differences of the barite aggregate specimens microstructure.

Słowa kluczowe:

barite ore, barite aggregate, microstructure, optical microscopy, thin sections analysis, X-ray tomography

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The paper presents investigation of the properties of the surface and the material stiffness – flexibility of series of samples taken from the sheds of the composite insulators. The insulators were previously subjected to wheel test. The wheel test and 1000 h salt fog test are regarded as alternative examination of the material resistance to the effects of electrical surface discharges. There were investigated two series of the samples of the composite insulators sheds. Examined specimens, made of HTV silicone rubber, were taken from the sheds of medium-voltage composite insulators of two different manufacturers. Insulators of both types passed the 1000 h salt fog test without reservation. Meanwhile, the wheel test can provide a basis for better distinguishing between physical properties of the tested materials. In the case of the insulators of one of the manufacturers the wheel test result was negative. Cross puncture effect of the sheds took place in several places. In addition, sheds were covered with dark coating of varying thicknesses. The results of the study indicated a significantly stronger influence of electrical and temperature factors on the sheds under investigations during the wheel test than in the case of the 1000 h salt fog test. It can be stated that these tests cannot be considered as alternative and it seems that wheel test enables better distinguishing between properties of the materials.

Słowa kluczowe:

composite insulators, silicone rubber, wheel test, electrical surface discharges, tracking and erosion

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Streszczenie:

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.

Słowa kluczowe:

carbon steel, austempering, lower bainite, acoustic emission (AE), neural networks

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The gas pressure infiltration technique was used to prepare Saffil alumina fibers reinforced Mg-Li and Mg-Li-Zn matrix composites with a dual-phase matrix structure. There was investigated the effect of variable Li content (6.2–10.3 wt.% Li) and Zn alloying (∼ 1.5 wt.% Zn) on the proof stress Rp0.2 of prepared composites. Rp0.2 values increased monotonously with rising fraction of Saffil fibers (5, 10 and 15 vol.%) reaching the maximum of about 250 MPa for Mg-Li matrix composites. Rp0.2 values of Mg-Li-Zn matrix composites were lower. Strengthening effect of Saffil fibers was promoted by the displacement redox reaction with Mg-Li and Mg-Li-Zn melts in which only Li significantly participated. Zn alloying retarded the displacement redox reaction. Too extensive reaction, however, resulted in the fiber damage and the drop in composite strength.

Słowa kluczowe:

Mg-Li alloys, Saffil fibers, metal matrix composites, short-fiber strengthening, reactive wetting, displacement reactions

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Research results on both mechanical and acoustic emission (AE) behavior of Mg-Li and Mg-Al alloys matrix composites (AMC) reinforced with ceramic δ-Al2O3 or carbon fibers subjected to the channel-die compression at room and elevated temperatures are presented in this paper. The AE measurements at room temperature showed that, the effect of anisotropy of the fibres distribution (random planar distribution) with respect to the compression axis appeared in the most investigated composites, whereas the AE activity at 140°C revealed a two- range character and the rate of AE events at 140°C was higher than at room temperature. These effects are discussed in terms of both the differences in thermal expansion between the fibres and the matrix as well as the weakening of the coherency between the fibres and the matrix leading to stronger debonding effects at 140°C than at room temperature. The spectral analysis of AE signals was performed with the Windowed Fourier Transform method, which served to plot the spectral density of AE signal as a function of frequency. The alominous and corundum ceramics types were also investigated in order to illustrate the enhanced AE, which was related to the different crack paths in the final stages of the sample degradation. The results were also discussed on the basis of SEM images, including the in-situ observations of microcracking as well as the dislocation strain mechanisms and microcracking ones during the channel-die compression of the Mg-Li-Al AMC.

Słowa kluczowe:

composites, fibres microcracking, acoustic emission, strain mechanisms, dislocations

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In this paper a method of X-ray microtomography (micro-CT) was employed for a direct insight into a microstructure of fibre cement boards of different quality. Four specimens were subjects of examination. Two parameters were determined to characterize the level of compaction of fibres in concrete matrix: mean-square displacement of migrating virtual particles after 500,000 of time steps and a diffusive tortuosity. The results of the investigation had revealed that fibre cement boards differing in density produce different images after processing with micro-CT method. The effect of microstructure tightening due to saturation using dying agent was also detectable.

Słowa kluczowe:

Fibre cement boards, Delamination of fibres, Computational modelling, X-ray microtomography

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The paper concerns the application of the acoustic emission (AE) method for the determination of the mechanical properties of continuously cast industrial tin bronze CuSn6P, which reveals tendencies to unstable plastic flow connected particularly with the Portevin–Le Chatelier (PLC) effect. The relations between the jerky flow connected with the PLC effect, AE intensity and the evolution of a fracture of the investigated alloy subjected to the tensile and compression tests have been analyzed. It has been found that the intensity of the oscillation of stresses, observed on the curves σ–ε, coincides with the effect of the instability of plastic deformation PLC type and the recorded signals of the intensity of acoustic emissions. It has also been found that the increase of the tensile temperature in the investigated alloy involves changes in the mechanism of cracking from transcrystalline ductile to brittle intercrystalline, characteristic at the temperature of minimum plasticity (DMT).

Słowa kluczowe:

Copper alloy, Portevin–Le Chatelier phenomenon, Fractography, Acoustic emission, Intercrystalline fracture

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The paper presents the concept of mechanoacoustic testing of degradation processes of ceramic materials, which is applied to diagnose high voltage insulators in operation. The method depends on the application of slowly increasing compressive loading acting on the sample, with simultaneous recording of acoustic emission (AE) descriptors. The process of loading is continued to the destruction or stopped at different stresses, and the samples are subjected to microscopic examination. Microscopic analysis of the samples enables determining the effects of stress action. The results were compared with the images of similar materials obtained from the insulators after different periods of operation. On this basis, there were distinguished consecutive stages of ageing of electrotechnical porcelain materials and corresponding effects of their structure degradation. Using slowly increasing quasi-static compressive loading in a relatively short-term mechanoacoustic test makes it possible to get results similar to those of long lasting degradation effects in operated electroinsulating objects. Using this method there is possible to describe the factors which affect short and long-term mechanical strength of the tested materials. There is also possible assessment of the validity and application of the theories explaining the strength of porcelains. There was presented research of the influence of the mullite phase on the short- and long-term mechanical strength of electrotechnical porcelain of different types.

Słowa kluczowe:

Degradation, Stress, Insulators, Porcelain, Aging, Microscopy

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The results of the investigation of both mechanical and acoustic emission (AE) behaviors of Mg4Li5Al and Mg4Li4Zn alloys subjected to compression and tensile tests at room temperature are compared with the test results obtained using the same alloys and loading scheme but at elevated temperatures. The main aim of the paper is to investigate, to determine and to explain the relation between plastic flow instabilities and the fracture characteristics. There are discussed the possible influence of the factors related with enhanced internal stresses such as: segregation of precipitates along grain boundaries, interaction of solute atoms with mobile dislocations (Cottrell atmospheres) as well as dislocation pile-ups which may lead to the microcracks formation due to the creation of very high stress concentration at grain boundaries. The results show that the plastic flow discontinuities are related to the Portevin-Le Châtelier phenomenon (PL effect) and they are correlated with the generation of characteristic AE pulse trains. The fractography of broken samples was analyzed on the basis of light (optical), TEM and SEM images.

Słowa kluczowe:

lightweight alloys, Acoustic Emission, fracture, Portevin-Le Châtelier phenomenon, twinning, dislocations, shear bands

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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.

Słowa kluczowe:

porcelain insulating materials, ageing processes, acoustic emission (AE), optical microscopy

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Proof stress Rp0.2 of dual-phase α + β structured Mg-Li and Mg-Li-Zn alloys has been inspected in terms of the strengthening contributions of α- and β-phases. The alloys studied with a variable fraction of α- and β-phases have been subjected to compression straining tests, microhardness measurements and structural analysis by EDX and XRD. Alloying with 1.5 wt.% Zn results in the hardening of both α- and β-phases which however exhibit different hardening responses due to different Zn enrichment. The rule of the mixture has been used to interpret Rp0.2 values by taking into account the fraction of α- and β-phases and their strength level represented by their microhardness. Compression stress-strain curves indicate that work hardening of alloys studied depends considerably on the fraction of α-phase and is higher for Zn-containing alloys.

Słowa kluczowe:

Mg-Li, Mg-Li-Zn, dual-phase alloy, solution hardening, ageing, work hardening

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W artykule przedstawiona została możliwość lokalizacji delaminacji w płycie włóknisto-cementowej za pomocą specjalnie do tego celu skonstruowanego urządzenia wykorzystującego metodę ultradźwiękową i fale podłużne. Przeprowadzono badania na trzech rodzajach płyt. Stwierdzono, że proponowana metoda diagnostyczna umożliwia wykrywanie lokalnych nieciągłości, np. obszarów o obniżonej zwartości, czy delaminacji w płytach włóknisto-cementowych na obszarze średnicy wiązki metodą estymacji prędkości fali ultradźwiękowej. Zaletami metody są niewielkie wymiary urządzenia i krótki czas badania

Słowa kluczowe:

płyty włóknisto-cementowe, badania nieniszczące, ultradźwięki

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W artykule przedstawiono wyniki badań parametrów termicznych procesu twardnienia mieszanek betonowych, z których dwie wykonano z wykorzystaniem kruszyw stosowanych w produkcji betonów osłonowych (kruszywo magnetytowe oraz serpentynitowe), a trzecią, referencyjną, z wykorzystaniem kruszywa amfibolitowego. Na podstawie analizy dokonanych pomiarów temperatury wyznaczono parametry procesu twardnienia betonu (m.in. maksymalny przyrost temperatury, maksymalny gradient i in.). Jednocześnie rozwiązując numerycznie tzw. zagadnie-nie odwrotne wyznaczono parametry cieplne betonu w trakcie pierwszych 72 godzin twardnienia. Tą samą metodą wyznaczono również wartości funkcji źródła ciepła, a następnie na jej podstawie oszacowano ilość ciepła wydzieloną w procesie hydratacji cementu. Uzyskano dobrą jakościową zgodność postaci funkcji źródła ciepła oraz wykresów zmian temperatury w mieszankach. W toku analiz uzyskanych wyników wyraźnie zaznaczył się wpływ zróżnicowania parametrów cieplnych zastosowanych kruszyw. W przypadku mieszanki z kruszywem serpentynitowym dały się także zauważyć istotne różnice w przebiegu przyrostu temperatury (opóźnienie) w stosunku do pozostałych mieszanek

Słowa kluczowe:

młody beton, beton osłonowy, ciepło hydratacji, ciepło właściwe, współczynnik przewodzenia ciepła

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The work concerns the application of the acoustic emission (AE) method in testing the mechanical properties of continuously cast industrial tin bronze CuSn6P, which reveals tendencies to instable plastic flow connected particularly with the Portevin-Le Chatelier (PLC) effect. The relations between the jerky flow connected with the PLC effect, AE intensity and the evolution of a fracture of the investigated alloy subjected to the tensile test at a strain rate (?? ) of about 1.2·10-3s-1 in the range of temperatures (20÷400?C) has been analyzed. It has been found that the highest intensity of the oscillation of stresses, corresponding to the instability of plastic deformation PLC occurred at 200?C, whereas the maximum of the AE activity is at about 200÷250?C. The brittle intergranular fracture starts in the range of equicohersive temperature (TE) of about 200?C. Plastic deformation of the investigated alloy in the range of the temperature of minimum plasticity, amounting to about 400?C, results in intercrystalline fractures on the entire surface of the stretched samples.

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The results of the investigation of both mechanical and acoustic emission (AE) behaviors of Mg4Li5Al alloy subjected to compression and tensile tests at room temperature are compared with the test results obtained using the same alloy and loading scheme but at elevated temperatures. The main aim of the paper is to investigate, to determine and to explain the possible influence of factors related with enhanced internal stresses such as: segregation of precipitates along grain boundaries or solute atoms along dislocations (Cottrell atmospheres) or dislocation pile-ups at grain boundaries which create very high stress concentration leading to fracture. The results show that the plastic instabilities are related to the Portevin–Le Châtelier phenomenon (PL effect) and they are correlated with the generation of AE peaks. The fractography of breaking samples was analyzed on the basis of light (optical), TEM and SEM images.

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The paper presents a method of pore connectivity analysis applied to specimens of cement based composites differing in water to cement ratio. The method employed X-ray microtomography (micro-CT). Microtomography supplied digitized three-dimensional radiographs of small concrete specimens. The data derived from the radiographs were applied as an input into the application based on the algorithm called ‘random walk simulation’. As the result a parameter called diffusive tortuosity was established and compared with estimated porosity of examined specimens.

Artykuł prezentuje metodę wyznaczania parametru charakteryzującego intensywność połączeń mikroporów w zastosowaniu do próbek kompozytów z matrycą cementową, różniących się stosunkiem wodnocementowym. Metoda bazuje na wynikach badań z zastosowaniem mikrotomografii rentgenowskiej. Analizowano zdigitizowane zestawy danych, opisujące trójwymiarową reprezentację mikrostruktury niewielkich próbek wykonanych z betonu. Przygotowane w ten sposób skany mikrostruktury zastosowano jako dane wejściowe wprowadzone do oprogramowania wykorzystujacego algorytm ‘przypadkowo migrujących cząstek wirtualnych’. W ten sposób wyznaczono parametr mikrostruktury znany jako krętość dyfuzyjna. Parametr ten porównano z porowatością obserwowaną wyznaczoną dla zbadanych próbek przy wykorzystaniu analizy jasności voxeli w analizowanych próbkach.

Słowa kluczowe:

X-ray tomography, concrete microstructure, diffusive tortuosity

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The purpose of these investigations was to determine the effect of the strain rate on the phenomenon of a heterogeneous plastic deformation of the Portevin–Le Chatelier type while testing free compression of CuZn30 single crystals with a crystallographic orientation of [139] at 300°C. Moreover, the relations between the work-hardening curve s–e displaying the PLC effect and the characteristics of the signals of the acoustic emission generated in the uniaxial-compression test were determined. It was found that the process of plastic deformation of the tested single crystals in the analyzed range of the frequencies up to 35 kHz generates differentiated sources of acoustic-energy emission, mainly the impulsive emission generated by signal events, correlated with the oscillations of the stresses on the work-hardening curves s–e. The strain rate mainly causes the changes in the intensity of the oscillation typical for the PLC effect.

Słowa kluczowe:

plastic strain, Portevin–Le Chatelier effect (PLC), single crystals, copper alloys, compression test, acoustic emission (AE)

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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 [1¯3 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.

Słowa kluczowe:

plastic strain, Portevin - Le Chatelier effect (PLC), monocrystals, copper alloys, compression test, acoustic emission (AE)

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In the paper two advanced methods for testing cement based composites are described and compared. These are X-ray microtomography and optical microscopy. Microtomography supplies three-dimensional images of small concrete specimens. In the tomograms all cracks, pores and other voids and inclusions, that exceed a few micrometers, are shown. Such visualisation can become a valuable tool for analysis of the basic material properties. Images obtained on thin sections and analysed with various methods on optical microscopes supply additional information on material microstructure that cannot be obtained in tomograms. For example it is relatively easy to determine zone penetrated by CO2 ingress. These two methods, presented on examples of tests, complete each another in order to supply a set of information on composition and defects of tested composite materials.

Słowa kluczowe:

cement matrix composites, concrete deterioration, X-ray tomography, microscopic analysis, concrete microstructure

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The research was carried out on steel 100CrMnSi6-4 under isothermal austempering resulting in forming the duplex structure: martensitic and bainitic. The kinetics of transformation was controlled by the acoustic emission method. Complex phase transformations caused by segregation and carbide banding occur at the low-temperature heat treatment of bearing steel. At the temperature close to MS, a certain temperature range occurs where an effect of the first product of prior athermal martensite on the bainitic transformation can be observed. In the registered signal about 15 million various events were registered. There were considered three types of acoustic emission events (of high, medium and low energy), with relatively wide sections and with different spectral characteristics. It was found that the method of acoustic emission complemented by the application of neural networks is a sensitive tool to identify the kinetics of bainitic transformation and to show the interaction between martensitic and bainitic transformations.

Słowa kluczowe:

Bearing steel, austempering, lower bainite, acoustic emission, neural networks

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Mg and Mg-Li matrix composites were prepared by the melt infiltration of fibrous preform consisting of Saffil alumina fibers and the silica binder. During this process there has occurred decomposition of silica binder and/or surface silica film by displacement redox reactions and the reaction products were characterized using SEM, TEM, SAED, FTIR and XPS techniques. The only reaction products found in Mg infiltrated Saffil preform were MgO and Mg2Si. In Mg-Li melt infiltrated Saffil preform there was found besides MgO and Mg 2 Si also the non- crystalline phase that appears to be the lithium silicate xLi2O ySiO2. Binary lithium silicides and ternary magnesium-lithium silicides were not detected

Słowa kluczowe:

Mg-Li composites, Saffil fibers, silica binder, melt infiltration, XPS, FTI

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The paper presents the microscopic and mechanoacoustic study of degradation processes of the porcelain material C 110 type. Small-sized samples, derived from the low voltage insulator, were subjected to a slow, quasi-static compression, with simultaneous recording of acoustic emission descriptors. There were distinguished consecutive stages of the material degradation. Obtained results were compared with the images of the microstructure of low-voltage insulator materials after many years of operation. On this basis, there were distinguished the factors determinant of the short-term strength of porcelain and its resistance to ageing processes under operating conditions.

Słowa kluczowe:

electrical porcelain, microscopic analysis, acoustic emission, degradation of the porcelain

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This paper discusses the mechanical properties, microstructure and crystallographic texture of light alloys made on the base of aluminium, magnesium and lithium. An acoustic emission (AE) technique was applied to detect the moment of twinning or slip activation during compression and channel – die tests to extend the comprehension on the nature of the plastic deformation processes occurring in the investigated alloy s

Słowa kluczowe:

hcp metals, aluminium and magnesium alloys, plastic deformation, mechanical twinning, crystallographic texture, acoustic emission

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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.

Słowa kluczowe:

electrotechnical porcelain, porcelain degradation, acoustic emission (AE), microscopic analysis

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The paper deals with the problems related to the diagnostics of selected parts of modern Diesel engines. The evolution of mechanical properties of four alloys of Mg-Li-Al system and four composites made on the base of the alloys mentioned above, caused by variation of its composition was presented. The Acoustic Emission (AE) method applied to monitoring of degradation of mechanical properties of the alloys and composites was described. Moreover, the results of the investigation of failures occurring in the injectors of Common Rail Diesel engines per formed with the application of AE method were also reported.

Słowa kluczowe:

Diesel engines diagnostics, light alloys and composites, Common Rail fuel system, Acoustic Emission method

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As a measure to avoid thermally induced cracking in massive concrete, mineral admixtures are often added as a substitute for a certain portion of cement. This paper presents the results of testing in course of which the temperature was measured during hardening of concrete mixtures produced with addition of calcareous fly ash obtained from the Power Station in Bełchatów, Poland. The investigation covered 76 concrete mixtures produced with three different aggregates and diverse binder content. In the experimental part of the research, the thermal parameters of hardening concrete were determined with a specially developed method in which the mixture was placed in a one-dimensional mould which allowed for unrestrained flow of heat in one direction. The results of testing were used to assess the influence of the respective ingredients, in particular calcareous fly ash, on the rate of rise of the fresh concrete temperature, on the time of occurrence of the maximum temperature and on the temperature gradients. Finally, a formula for calculating the specific heat of hydration depending on the mixture composition was proposed.

Słowa kluczowe:

high calcium fly ash, fresh concrete temperature, heat of hydration, massive concrete, multicomponent cement, temperature gradient

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The investigation of concrete microstructure and phase composition was performed on concrete specimens produced with and without calcareous fly ash obtained from Bełchatów Power Station. The used calcareous fly ash (designated “W”) was either unprocessed or ground to assumed specific surface and added to concrete mix to substitute 30% of the binder by weight. The following testing methods were used in this research: scanning electron microscopy, differential thermal analysis (DTA) and multiple microindentation. The characteristic features of the investigated microstructures are discussed and the effect of calcareous fly ash on the content of non-evaporable water and portlandite in cement matrix is analysed. The results of microindentation and compressive strength testing were used as the basis for evaluation of the efficiency of calcareous fly ash added to concrete mix.

Słowa kluczowe:

calcareous fly ash, microindentation, microstructure, non-evaporable water, phase composition, portlandite, strength

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TiNi shape memory alloy (SMA) specimens have been subjected to tension carried out at various strain rates. The goal was to investigate a nucleation and development of the stressinduced martensitic transformation by infrared (IR) and acoustic emission (AE) techniques. Therefore, both the infrared radiation and acoustic emission data were recorded using a fast infrared camera and acoustic emission set-up, respectively. It has been shown that the initial, macroscopically homogeneous transformation initiates in the elastic stage of the deformation even before the stress-strain curve knee and formation of the localized transformation bands. It has also been found that the homogeneous transformation occurs at similar stress level for all strain rates applied, while the localized martensitic transformation depends on the strain rate. Nucleation and development of the localized transformation bands, detected by the infrared camera, were confirmed by acoustic emission technique. The differences between the IR and AE activities were recorded during the TiNi SMA loading and unloading process, manifesting different dynamics of the stress-induced martensitic forward and reverse transformation.

Słowa kluczowe:

shape memory alloy, TiNi, superelasticity, martensitic transformation, tension test, acoustic emission

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W pracy przedstawiono badania wpływu fazy mulitowej na krótko- i długotrwałą wytrzymałość mechaniczną elektroporcelan 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.

Słowa kluczowe:

porcelana elektrotechniczna, degradacja tworzyw porcelanowych, emisja akustyczna, badania mikroskopowe

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The objective of this investigation was to test the effectiveness of the Acoustic Emission (AE) measurements in determining the critical stresses during four-point bending of mortar beams. Within the measuring procedure the parameter σcr/σ300 was calculated and analysed. Additionally, the influence of cement replacement by high calcium fly ash (HCFA) on the process of crack healing was discussed. Mortar beams with different content of HCFA and reinforced by steel microfibres were prepared for tests. After curing in standard conditions the beams were subjected to four-point bending test in order to introduce the pre-cracking. Thereafter the beams were cured in the lime water and loaded after 56 and 112 days in the same way as for the first time. Additionally the microstructure of mortars was studied in a stereo optical microscope as well in an electron scanning microscope including the Energy Dispersive X-ray analysis (EDX). The results of microstructural characterization of mortar containing HCFA from lignite combustion are presented. The applied load level slightly exceeded the critical stress, producing intense crack growth processes however did not significant affected the load capacity of the beams. During the consecutive loading the decreasing tendency of σcr/σ300 ratio was noted. The obtained results confirm that the latter parameter can be applied as a measure of the composite degradation level for the elements carrying the repeated loads of amplitude close to the critical stress of the structure and also that the cement replacement with HCFA influences the process of crack healing.

Słowa kluczowe:

critical stress, Acoustic Emission, microcracking, self-healing, concrete microstructure, fly ash

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Mortar beams were cast with various content of high calcium fly ash as a partial replacement of Portland cement. The results of microstructural characterization of mortar containing fly ash class C (High Calcium Fly Ash – HCFA) from lignite combustion are presented. The evaluation of the microstructure was performed using SEM and optical microscopy. At the age of 28 days the beams were subjected to 4-point bending until opening of a system of microcracks and cracks. Then, the beams were cured in lime water for 56 and 112 days after precracking and again subjected to loading. The results in a form of partial self-healing were recorded with load-deflection curves and using optical methods. The results show the percentage of replacement of cement by fly ash influenced the process of crack healing.

Słowa kluczowe:

Microcracking, Self-healing, Microstructure, Fly Ash

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There has been proposed an innovative thermal treatment of bearing steel 100CrMnSi6-4, where the existing standard heat treatment has been replaced by austempering. The structure of low-temperature tempered martensite has been replaced by a microstructure composed of martensite and lower bainite with midrib. The kinetics of bainitic transformation and isothermal martensitic transition at selected austempering temperatures was controlled by acoustic emission. The research on contact strength was made under the conditions of rolling-sliding friction. The microstructure was revealed with the use of a light microscope and the forms of pitting wear were displayed by a scanning electron microscope. It was found that the optimum microstructure providing the best used contact strength of the tested steel is conditioned by the formation of a lower bainite with midrib at the temperatures near MS. A plausible cause of the increased resistance to pitting is bifurcation of fatigue cracks on dispersion bainitic carbides in combination with primary carbides, in bainitic-martensitic matrix.

Słowa kluczowe:

Acoustic Methods, Bainite, Bearing Steels, Isothermal Heat Treatment, Midrib, Pitting, Rolling Contact Fatigue (RCF)

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W artykule przedstawiono powstawanie sygnału emisji akustycznej (EA) oraz wykorzystanie tego sygnału w diagnostyce obiektów technicznych. Opisano własności sensorów EA i aparaturę do rejestracji sygnału. Przedstawiono przykładowo trzy obszary zastosowania metody EA w technice: monitorowanie stanu technicznego konstrukcji żelbetowych, zbiorników ciśnieniowych i mostów stalowych. Rejestrowanie i analizowanie sygnału EA okazało się skutecznym narzędziem, rozwijanym w wielu laboratoriach i stosowanym coraz powszechniej w diagnostyce konstrukcji.

Słowa kluczowe:

badania nieniszczące, diagnostyka zbiorników ciśnieniowych,eksploatacja obiektów żelbetowych, emisja akustyczna

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The paper deals with the effect of Al content in two-phase Mg-10Li-xAl (x = 0, 1, 5) alloys on their straining behavior before and after severe plastic deformation by high pressure torsion. Both coarse-grained and ultrafine-grained alloys were compression strained in channel-die device with simultaneous acoustic emission monitoring. It has been observed that Hall-Petch strengthening in ultra-fine grained alloys superposes with the strengthening resulting from Al alloying (solution hardening, particulate strengthening). Superposition of these strengthening mechanisms becomes stronger with increase in Al content, presumably due to enhanced grain refining effect.

Słowa kluczowe:

Mg-Li-Al alloys, grain refinement, high pressure torsion, acoustic emission, Hall-Petch strengthening

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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.

Słowa kluczowe:

aluminous porcelain, structural degradation, acoustic emission (AE), microscopic analysis

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This experimental paper comprises the results of acoustic emission (AE), microscopic and ultrasonic measurements of samples subjected to slowly increasing compressive stress. On the basis of conducted measurements the successive stages of the material structural degradation have been recognized. The objects of study were samples made of C 120 aluminous porcelain. The investigated material has found at present the application in the fabrication of technical elements like overhead power line insulators. In the case of such objects, not only high mechanical strength, but especially elevated durability as well as operational reliability are required. The expected „life time” of net insulators during exploitation is about 40 years. The analysis of obtained mechanoacoustic dependences pointed out a complex mechanism of degradation of the material. Microscopic investigation of samples, which were stressed to different levels of load, enabled to specify the development of gradual growth of microcracks and successive crushing out of elements of the structure. These processes appear to be similar to the ageing processes occurring in the material during long period of exploitation under a working load. Three stages of the structure degradation were distinguished. The preliminary and subcritical ones show low or moderate intensity of AE signals and considerable variety for the particular samples. The critical stage directly precedes the destructtion of samples. Its range is relatively narrow and reveals the AE activity of high energy. 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.

Słowa kluczowe:

aluminous porcelain, ceramic insulators, insulator testing, acoustic emission, microscopic analysis, structural degradation

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The paper presents a nondestructive ultrasonic method of investigating long-rod insulators used on overhead power lines and in substations. A correlation between the degree of degradation of porcelain C 120 and the ultrasonic wave propagation and attenuation parameters was established. The ultrasonic method was used to analyze the quality of groups of line and post insulators after many years of service. Also a new mechanoacoustic method of investigating the stages in the degradation of insulator porcelain was applied. As a result of the investigations carried out on samples of porcelain C 130 the successive stages in the degradation of ceramic insulators during their service life were determined.

Słowa kluczowe:

Ceramic insulators, insulator testing, acoustic measurements, ultrasonic applications, acoustic emission

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

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acoustic emission (AE), material degradation, electrotechnical ceramics

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The objective of the presented investigation was to design the computer-aided procedure to assist the concrete component identification using microhardness testing method and the experimental verification of its efficiency by examination of concrete specimens. Two algorithms of analysis of Acoustic Emission (AE) signal evoked during microindentation were applied. AE signal processing was made by means of computer programs enabling for integrated processing of registered data. Data sets created during microindentation processes were analysed in order to distinguish indents in cement matrix, in aggregate grains and in other areas. The most efficient of the proposed selective criterions, used within a computer software based on wavelet filtering of the recorded AE signal, enabled for successive recognition of concrete components with the efficiency of 76 % within the tested population.

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acoustic emission, microhardness, phase recognition, testing method, wavelet filtering

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This paper presents the results of acoustic emission (AE) measurements of samples under compressive stress. Additional research, concerning structure and parameters of the material, was performed using microscopic and ultrasonic methods. The object of the investigation were samples of porcelain material C 130 type of domestic long-rod insulator LP 75/31W. This kind of aluminous porcelain demonstrates high mechanical and electrical strength as well as resistance to aging degradation processes. It finds wide application in modern electrotechnical engineering. The aim of this study was to recognize stages of degradation processes of the porcelain structure. The present work constitutes a continuation of the study concerning the influence of technological faults, existing in porcelain material structure, on long-term mechanical strength. These results were presented at the OSA Conference in 2006. The analysis of mechanical-acoustic characteristics pointed out diversified strength and complicated mechanism of the material degradation. The effectiveness of the dispersive and fibrous reinforcement of aluminous porcelain C 130 type was ascertained. It was stated during the microscopic investigation that the structure of the material is different from that in the case of typical aluminosilicate ceramic materials. The main reason for this effect is due to densely dispersed corundum and mullite fine crystals in glassy matrix.

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porcelain material C 130 type, acoustic emission, compressive strength, structural degradation

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The paper presents the investigations of the relation between the acoustic emission (AE) and the Porte vin-Le Chatelier (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

Słowa kluczowe:

acoustic emission (AE), Portevin-Le Chatelier (PL) effect, tensile test, dislocations, strain mechanism, nanocrystalline and/or ultra fine-grained structure, accumulative rollbonding (ARB)

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Ultrasonic, microscopic and acoustic emission (AE) methods were applied to investigate the microstructure of composite rods, used as a carrying element of the medium voltage insulators. Such features of material structure as homogeneity level and the appearance of defects were discussed. The research was aimed at determining the influence of the technology of epoxy-glass fabrication on quality parameters of the insulator rods. The results of acoustic testing were compared with the effects of microscopic investigation.

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composite insulator, epoxy-glass material, nondestructive ultrasonic measurements, acoustic emission

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Słowa kluczowe:

acoustic emission, plate vibrations, frequency spectrum

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W wyniku doświadczeń zebranych w trakcie serwisowania silników wysokoprężnych diagności dokonali zestawienia procentowego udziału najczęstszych przyczyn awarii tych maszyn. Należą do nich awarie: układu paliwowego, sterowania, układu tłokowo-korbowego. Przewaga awarii układu paliwowego wynika z faktu, że poprawne działanie tego układu zależy od stanu bardzo precyzyjnych elementów działających w warunkach występowania wysokiego ciśnienia i znacznych przyspieszeń typu impulsowego, przy czym niewielkie uszkodzenia mechaniczne tych elementów, wpływ wysokiej temperatury i osadzanie się cząstek niespalonego węgla (nagaru) wywołują niekorzystny wzrost lub zmniejszenie się dawki wtryskiwanego paliwa. Najczęstszym uszkodzeniem układu wtryskowego zasobnikowego, to jest pracującego w układzie Common Rail (C-R). jest awaria zaworu sterującego dawką paliwa we wtryskiwaczu, powodująca jego nadmierny wypływ do kanału przelewowego i spadek ciśnienia w zasobniku. Nie stwierdzono, aby przyczyną tego uszkodzenia było naturalne zużycie elementu, ponieważ wykrywano awarie zarówno po kilkudziesięciu jak po kilkuset godzinach eksploatacji silnika. W związku z tym opracowano procedury diagnostyczne mającą na celu identyfikację niesprawnego wtryskiwacza. Niektóre z procedur wymagają umieszczenia wtryskiwacza w zewnętrznym urządzeniu diagnostycznym, a inne można stosować w trakcie jego pracy na działającym silniku

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The paper describes two different techniques of ultrasound measurements performed in fibre cement boards, the material widely applied in building technology. An in-house device dedicated for fibre-cement board testing is also presented. To overcome the difficulty of determining the arrival time of the waveform of a longitudinal wave travelling across a thin and inhomogeneous body, a cross-correlation method of signal processing was proposed and applied

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ultrasound, fibre-cement board, waveform cross correlation coefficient

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Nuclear reactor containments must maintain high durability since they restrict the spread of radiation and radioactive contamination to the general public, which could have significant consequences. The containment integrity and impermeability for potentially contaminated media is ensured using sophisticated structural and materials solutions including prevention of early age cracking of concrete. The results of numerical and experimental investigation on thermal behavior of early age concrete are presented. Concrete mixes were prepared with low-heat blended cements and various mineral aggregates. Special aggregates were selected for enhancing the radiation shielding capacity of concrete, including minerals of high atomic weight and of increased content of bound water. The proposed approach consisted of several stages, consisting mainly of measurements of the one-dimensional heat distribution in cylindrical concrete elements and solving the equation of one-dimensional heat transferto determine thermal properties of hardening concrete. The proposed model of temperature distribution in hardening concrete is based on the non-linear inverse heat transfer problem solution. The obtained experimental results and numerically determined material characteristics are discussed in respect to the concrete mix design.

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durability, heat transfer, hardening concrete, inverse solution, temperature, thermal properties

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In the paper a method of X-ray microtomography (micro-CT) was employed for a direct insight into a microstructure of concrete with a practical resolution of approx. 10 micrometers3. Two sets of specimens were subjects of examination. The spatial concentration of air pores was investigated in three concretes differing in the amount of the supplement of high calcium fly ash (HCFA). The parameter of pore connectivity called diffusive tortuosity was determined in three other concretes made of the same ingredients but differing in water to cement ratio. The quantitative results obtained with application of described procedures are applicable in material characterization.

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X-ray microtomography, concrete, microstructure

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The object of investigation was the behaviour of acoustic emission (AE) during channel-die compression of the Mg-Li-Al alloys matrix composites (AMC) reinforced with ceramic δ-Al2O3fibres at room and at elevated temperature. The results of AE measurements at room temperature showed that in the majority of the investigated compositions the effect of anisotropy of the fibres distribution (planar random distribution) appeared with respect to the compression axis, whereas the AE activity at 1400C revealed a two-range character and the level of the rate of AE events was higher than thatat room temperature. These effects are discussed in terms of both, the differences in thermal expansion as well as weakening of the coherency between the fibres and the matrix. The results of AE measurements served to plot the spectral characteristics of the registered AE signals, i.e. the spectral density of AE signal as a function of its frequency. The spectral analysis of AE signals generated during the micro-cracking process of ceramic fibres in channel-die compressed Mg-Li-Al AMC was performed with the Windowed Fourier Transform method. The results are also discussed on the basis of optical and scanning microstructure images including these in-situobservations of microcracking fibres as well as in the context of the dislocation strain mechanisms and microcracking ones during the channel-die compression of the Mg-Li-Al AMC.

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The durability of concrete in outdoor structures is closely related to its resistance against the aggressive gaseous actions coming from the environment and including influence of oxygen, nitrogen, carbon dioxide. The pore system and its interconnectivity in the concrete matrix directly influence the possibility of penetration of various aggressive gaseous media into concrete structure. The X-ray microtomography (micro-CT) is a modern, non-invasive technique enabling for determination of existing pores in the microstructure of concrete matrix. In the paper the results of investigation of two different concretes by the application of micro-CT method to micro-cores are presented. The quantitative information on the parameters of the analysed microstructure can improve the methods of material characterization available up to now.

Słowa kluczowe:

X-ray microtomography, concrete, microstructure

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