Wyniki 1-9 spośród 9 dla zapytania: authorDesc:"ANDRZEJ PIĄTKOWSKI"

Low temperature deformation twinning in channel-die compressed aluminium single crystals evidenced by Acoustic Emission

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It is commonly believed that twinning is the most efficient source of acoustic emission [1÷5] due to fast release of great amount of elastic energy. It is connected with the fact, that the velocity of twinning dislocations is higher from this of slip dislocations [4], which results in the increase of contribution of accelerating effects in the recorded AE impulses. Very often acoustic emission induced by twinning contains also an audible range. Hence, more or less loud characteristic knocks during deformation can be heard. One of the first AE investigations concerned the tensile test of titanium and its alloys [1], in which it was established, that the AE activity in Ti was bound with twinning from the beginning, while in Ti alloys the AE impulses from twinning appeared after a high degree of deformation. During compression of the γ-TiAl alloy, AE sources were identified as generally coming from slip, twinning and the appearance and development of microcracks. It was reported that “the detailed mechanisms by which moving dislocations create elastic waves are not fully understood" [3]. Moreover, the problem of twinning in Al has still remained controversial. In available literature authors did not find any data on this subject. It is believed quite commonly, that at least in simple uniaxial strain state - like in a tensile test - twins do not appear in Al. The aim of this work is to demonstrate, that there are numerous proofs that in a complex strain state, which occurs in the channel die compression of single Al crystals at temperature of liquid nitrogen the twinning processes do occur. MATERI ALS AND MET HODS The single crystals of Al and Ag (for comparison) were produced with the Bridgman method, of which samples of dimensions 10×10×10 mm of orientations {112}<111> and {531}<231> for Al and {112}<111> for Ag were cut out. The single crystals were subjected to tests of channel-die compression at temperature of liq[...]

Mechanical-acoustic study of degradation processes of ceramic structure illustrated by corundum material

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The paper presents the results of microscopic, ultrasonic and acoustic emission (AE) investigations of corundum ceramic material C 799 kind samples, exposed to compressive stress. On the basis of AE measurements of slowly compressed samples, the successive stages of structural degradation have been recognized. Investigations revealed that differences registered for the strength and the mechanica[...]

Foundations of mechanoacoustic method of material degradation research

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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. Streszczenie. W pracy została przedstawiona koncepcja mechaniczno-akustycznych badań procesów degradacji ceramicznych tworzyw elektrotechnicznych. Małogabarytowe próbki poddawane były wolno narastającemu obciążeniu ściskającemu z jednoczesną rejestracją deskryptorów emisji akustycznej. Proces prowadzono do zniszczenia lub zatrzymania na różnych etapach degradacji struktury. Analiza mikroskopowa próbek pozwoliła określić efekty oddziaływania naprężeń. (Podstawy mechanoakustycznej metody badań degradacji materiałów). Keywords: acoustic emission (AE), material degradation, electrotechnical ceramics. Słowa kluczowe: emisja akustyczna, degradacja materiału, ceramika elektrotechniczna. Introduction Ceramic materials, especially electrotechnical porcelains, are widely applied to fabricate reliable electroinsulating elements. Porcelain is used to produce line, post and traction insulators as well as hollow insulators of high parameters. For these products, besides high mechanical strength, a long period of exploitation without breakdown is required. Increasing tendency for production of aluminous porcelain of high mechanical strength (C 130 type) has been observed for several years. This is the result not only of the present requirements concerning the shortterm mechanical strength of the electroinsulating elements. This material is suitable to guarantee the reliability of power supply, which is determined by the durability, i.e. by the long-term mechanical strength of the ce[...]

Experimental evaluation of resistance to degradation of modern C 120 type porcelain

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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. Results of experiments revealed high long-term mechanical resistance of tested material, when compared to typical C 120 porcelains. Streszczenie. 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. Stwierdzono wysoką krótko- i długotrwałą odporność materiału izolatora w porównaniu do typowych tworzyw rodzaju C 120. (Eksperymentalna ocena odporności nowoczesnej porcelany rodzaju C 120 na procesy degradacji). Keywords: ceramic insulators, porcelain degradation, acoustic emission (AE), microscopic analysis. Słowa kluczowe: izolatory ceramiczne, degradacja tworzyw porcelanowych, emisja akustyczna, badania mikroskopowe. Introduction The aluminous porcelain of C 120 type has at present wide application in the production of reliable electroinsulating elements of power systems. Line and station MV insulators, hollow insulators as well as bushings are produced using this kind of ceramic material. The reliability of power supply is determined primarily by the durability, closely connected with the long-term mechanical strength of insulators. That is why these properties are the most important in the case of such objects. The evaluation of operating time of the porcelain material is based mainly on the analysis of the [...]

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

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The Mg-Li alloys and the composites based on these materials have been still attractive candidates for light and tough construction materials for the application in automobile (e.g. car engine housings), aviation and space industries. The alloys can occur in three different phase areas. The alloys containing up to 4 wt. % Li consist of α phase of hexagonal lattice A3 (hcp), while these with above 12 wt. % Li are in the form of β phase, which is cubic A2 (bcc). The alloys of Li content from 4 up to 12 wt. % are two-phase and occur as the mixture of α+β phases. The mechanical properties of the α phase are worse than these of the β phase, which reveals very good plasticity [1]. The methods of intensive deformation have recently been more frequently applied [2÷4] in order to obtain ultra fine-grained refinement which ensures high strength and plasticity as well as prospects for the superplastic flow of the material in conditions of relatively low temperatures [2]. The AE technique has been still helpful in the examinations of deformation mechanisms, particularly regarding the mentioned materials of ultra fine-grained (nonocrystalline) morphology obtained after processing with intensive strain methods [2, 3, 7, 8]. The aim of the research was to describe and explain the correlations between the proceeding of the generated AE signals and the mechanisms of plastic (or possible superplastic) deformation in the Mg-Li alloys subjected to compression tests in the channel-die before and after the application of HPT technique. EXPERI MENT AL MET HODS The Mg-9Li alloys were produced within the cooperation with the Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, Bratislava, Slovakia. The material was obtained by melting magnesium and lithium of 99.99 and 99.5 % purity, respectively in a Ba[...]

Microstructure and mechanical properties of the Cu/SnAuCu/Cu joints

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The European Union regulations forced the manufactures to limit the use of certain hazardous substances such as cadmium and lead in the electrical and electronic equipment and also make them responsible for its storage and recycling [1, 2]. In a consequence the lead-free interconnection technology is one of the most active branches of the nowadays materials science. PbSn replecements are mainly the tin alloys, among which a special class are those consisted of tin and noble metals such as copper, silver and gold. They are possesing two characteristic features - the high melting point and high concenteration of Sn compared to that of eutectic PbSn. Moreover, the composition of the lead-free solders can be described as eutectic or near-eutectic, which ensures the best manufacturability. The microstructure of these solders is a mixture of tin and the intermetallic phase (IP). Since both mechanical and electrical properties of the tin are anisothropic they are also anisothropic in the case of eutectic solders. Therefore, the intermetallics may take a form of the inhomogenous structures (for example Ag3Sn in the shape large plate-like crystals). To avoid of such IP creation the concentartion of silver in SnAg solder should be less than 3% wt. and copper should not go over than 0.7% wt. in SnCu solders. In the case of SnAu solders gold must not exceed the value of 5% wt. otherwise it leads to the formation of AuSn4 phase which causes britlle “cold" joint. Ternary solders are mainly SnAgCu solders (SAC) where the amounts of silver and copper (corresponding to the eutectic composition) are 3.5±0.3 and 0.9±0.2 (wt. %), respectively [3÷5]. Other ternary solder is SnAuCu alloy which may be used as a joining material for the joints in so-called noble electronics. They are applied in devices with the highest degree of reliability, such as biomedical devices. It should be noted that such products after their exploitation und[...]

Rola fazy mulitowej w podwyższeniu odporności elektroporcelan na procesy starzeniowe

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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. Abstract. The paper presents the research of the influence of the mullite phase on the short- and long-term mechanical strength of the electrotechnical porcelain of different types (C 110, C 112, C 120 and C 130). The total mullite phase content, size and distribution of precipitates and dispersed single crystals in the glassy matrix were considered. During investigation mechanoacoustic and microscopic techniques as well as ultrasonic testing were used. The role of the mullite phase in the increase of resistance to aging processes of electrical porcelain of various types was described. (Influence of the mullite phase on the increase of resistance to aging processes of different types of electrotechnical porcelain). Słowa kluczowe: porcelana elektrotechniczna, degradacja tworzyw porcelanowych, emisja akustyczna, badania mikroskopowe. Keywords: electrotechnical porcelain, porcelain degradation, acoustic emission, microscopic analysis. Wstęp Prowadzone od XIX wieku badania wytrzymałości mechanicznej tworzyw porcelanowych doprowadziły do wyróżnienia kilku najważniejszych hipotez dotyczących możliwości podwyższenia właściwości mechanicznych materiału. Niezależnie od wad, które mają bardzo istotny wpływ na wytrzymałość, wyróżnia się trzy zasadnicze teorie. Opisują one zależność właściwości mechanicznych porcelany od budowy fazowej czerepu [1, 2]. Pierwsza teoria - mulitowa jest tematem niniejszej pracy.[...]

Influence of microstructure on the properties of siliceous electrical porcelain DOI:10.12915/pe.2014.10.28

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The paper presents the microscopic and mechanoacoustic study of degradation processes of the porcelain material C 110 type. Smallsized 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. Streszczenie. W pracy przedstawiono mikroskopowe oraz mechanoakustyczne badania procesów degradacji w tworzywie porcelanowym rodzaju C 110. Próbki małogabarytowe, pochodzące z elementu elektroizolacyjnego niskiego napięcia, poddawane były powolnemu, quasi-statycznemu ściskaniu, z jednoczesną rejestracją deskryptorów emisji akustycznej. Na podstawie badań mikroskopowych ściskanych próbek wyróżniono etapy degradacji materiału. Wyniki konfrontowano z obrazami mikrostruktury tworzywa izolatorów niskonapięciowych po wieloletniej eksploatacji. Wyróżniono czynniki mające wpływ na wytrzymałość krótkotrwałą oraz odporność tworzywa na starzenie się w warunkach eksploatacyjnych. (Wpływ mikrostruktury na właściwości kwarcowej porcelany elektrotechnicznej). Keywords: electrical porcelain, microscopic analysis, acoustic emission, degradation of the porcelain. Słowa kluczowe: porcelana elektrotechniczna, badania mikroskopowe, emisja akustyczna, degradacja tworzyw porcelanowych. doi:10.12915/pe.2014.10.28 Introduction The composition of European hard porcelain - with a high content of clay minerals - was finally developed around 1720. Besides clay raw materials - in the amount of about 50% - there is used about 25% of feldspar fluxes and the same quantity of quartz as a filler. These propo[...]

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