157 research outputs found

    Granulocitna rezerva u kronignom eksperimentalnom otrovanju benzenom u Ŕtakora

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    The normal two-fold increase in granulocytes in the peripheral circulation induced by corticosteroids was almost abolished in chronic benzene poisoning in rats.Normalno očekivani dvostruki porast granulocita u perifernoj cirkulaciji nakon primjene kortikosteroida izostao je u Ŕtakora kronično otrovanih benzenom

    Lead metabolism with special reference to the problem of population exposure

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    U članku je dat prikaz suvremenih shvaćanja o rnetabolizmu olova i njegovim toksičnim učincima. Za razliku od dosadaÅ”njeg promatranja olova kao profesionalnog otrova težiÅ”te je postavljeno na problem ekspozicije cjelokupnog stanovniÅ”tva tim metalom i njegovim mogućim učincima na zdravlje. Zbog toga je posebno obrađen problem trovanja djece olovom kao i metabolizam olova u graviditetu i laktaciji. Na kraju je upozoreno na druÅ”tveno-ekonomsko značenje opće kontaminacije olovom koja uslijed naglog razvoja motorizacije zahvaća i naÅ”e krajeve.Current views on lead metabolism and its toxic effects are surveyed. The problem of lead is no longer considered from the point of view of occupational intoxication, but attention is focussed on total population exposure to lead and its possible health effects. The problem of lead poisoning in children as well as of lead metabolism in pregnancy and lactation is therefore dealt with separately. At the end a varning is given about social and economic significance of general lead contamination which is spreading over the country owing to the fast development of motorization

    A new methodology for prediction of high-cycle contact fatigue for spur gears

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    High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

    Determination of critical size of corrosion pit on mechanical elements in hydro power plants

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    Researchers in the field of fracture mechanics, predominantly developing appropriate solution algorithms for problems of solid bodies with cracks. Problems in mechanics generally, related with fracture and fatigue for solid bodies with various geometries of sharp notches, are studied to a much lesser extent. This situation can be explained by analytical difficulties arising in solving problems of elasticity theory for bodies with rounded notches. To solve problems of such class, starting from data on stress concentration in the rounded notch tip with a significant radius of curvature, simplified solutions with are therefore of great importance. Recent years, due to constant rise of computing power and development of numerical methods, re-evaluation of stress concentration factors from a viewpoint of theory of elasticity is present. This is mainly as a feedback from industry, which have requirements toward mega and nanostructures. Corrosion represents an important limitation to the safe and reliable use of many alloys in various industries. Pitting corrosion is a form of serious damage on metals surface such as high-strength aluminum alloys and stainless steel, which are susceptible to pitting when exposed to a corrosive attack in aggressive environments. This is particularly valid for dynamic loaded structures. The basic idea behind this paper is finding links between different scientific and engineering disciplines, which will enable useful level of applicability of existing knowledge. The subject of this paper is application of new method of determine length scale parameter for estimating the mechanistic aspect of corrosion pit under uniaxial/multiaxial high-cycle fatigue loadingā€¦

    A new methodology for prediction of high-cycle contact fatigue for spur gears

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    High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

    Combined load simulation vs component loads simulation in machine design: A case study

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    Na sadaÅ”njem nivou razvoja tehnologije, u stvarnim radnim uslovima, gotovo svi maÅ”inski elementi su opterećeni kombinovanim opterećenjima. Cilj istraživanja prikazanog u ovom radu je ukazivanje na značaj proračuna nosivosti maÅ”inskih elemenata simuliranjem kombinovanog opterećenja. Istraživanje prikazano u radu inspirisano je jednim stvarnim otkazom turbinskog vratila hidroturbine. Vratilo sa prirubnicom i visokim odnosom prečnika vratila i prirubnice bilo je predmet obimnih proračuna u cilju pronalaženja uzroka otkaza. Klasični analitički proračun ovog vratila koristi Peterson-ov faktor koncentracije napona i proračun maksimalnih napona za pojedine naponske komponente kombinovanog opterećenja, a onda analitičku vrednost ukupnog napona proračunava na osnovu hipoteze o maksimalnom normalnom naponu. Sa druge strane, prikazani proračun naponskog stanja vratila metodom konačnih elemenata bazira se na simuliranju realnih radnih opterećenja u uslovima kombinovanog opterećenja istovremenim definisanjem svih komponenti (savijanja, uvijanja i zatezanja). Oba proračuna urađena su za nekoliko različitih radijusa na prelazu vratila ka prirubnici. Dobijeni rezultati prikazani su uporednim dijagramima dobijenih vrednosti ukupnih napona i odgovarajućih faktora koncentracije napona. Analiza ovih dijagrama vodi do zaključka da proračun ukupnog napona u slučaju kombinovanog i složenog opterećenja na bazi Peterson-ovih faktora koncentracije napona i standardnog analitičkog postupka treba da bude zamenjen naprednim tehnikama proračuna koji obezbeđuju tačnija reÅ”enja koja se istovremeno i jednostavnije analiziraju i koriste.At a present level of technology, almost all machine parts are subjected to combined loads in real working condition. The aim of research described in this paper is to highlight the importance of combined load simulation for the calculation of machine parts load capacity. This research is inspired by one failure case study of hydro turbine shaft. The shaft with flange and high ratio of shaft/flange diameter is the subject of excessive calculation in order to find the cause of failure. The classic analytical calculation of this shaft uses the Peterson's elastic stress concentration factor and calculates stress concentration factors and maximum stresses for different stress components of combined load and then calculate analytical values of total stress by the hypothesis of maximum normal stress. On the other hand, presented Finite Element Analysis simulates shaft stress state under real conditions of complex load by simultaneously applying all load components (bending, torsion and tension). Both of the calculations are performed for few different radii in shaft-flange sections. The results are presented by comparative diagrams for obtained values of total stresses and stress concentration factors. The analysis of these diagrams leads to conclusion that the use of Peterson's stress concentration factors and standard analytical techniques for total stress calculation has to be replaced with modern calculation techniques that provide a more accurate, easier-to-handle solution

    Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

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    This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

    Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

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    This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

    Production of scientific and technical information in the institute for medical research and occupational health in the past decade (1968-1977)

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    Analizirana je produkcija znanstvenih i stručnih publikacija u Institutu za medicinska istraživanja i medicinu rada u Zagrebu u desetljeću 1968. - 1977. Ukupna informacijska produkcija podijeljena je u tri razreda: (A) primame znanstvene publikacije, (B) sekundarne publikacije (primjena i prijenos znanja) i (C) istraživački izvjeÅ”taji. Prva dva razreda podijeljena su u po nekoliko podrazreda - kategorija. PridruživÅ”i svakoj kategoriji određeni broj bodova (informacijskih jedinica), može se ukupna produkcija prikladno analizirati s obzirom na međuodnose pojedinih vrsti aktivnosti Instituta, utjecaj financiranja, kvalitetu i informacijsku produktivnost pojedinih organizacijskih jedinica. Stoga opisana metoda klasifikacije i enumeracije daje mnogo bolji uvid u kvalitetu i strukturu znanstvenih i stručnih publikacija nego puko prebrojavanje objavljenih naslova.The production of scientific and technical papers in the Institute for Medical Research and Occupational Health in the 1968-1977 decade was analysed. Overall information production was divided into three classes: (A) primary scientific publications, (B) technical papers (application and transfer of the existing knowledge), and (C) research project reports. The first two classes were subdivided into several categories. To each category a certain number of Ā»information unitsĀ« was assigned. In this way, the overall production could be suitably analysed with respect to the interrelationships of particular activities of the Institute, the effect of financing, and quality and information productivity of individual laboratories. Therefore, the described method of classification and enumeration gives a much better insight into the quality and the structure of scientific and technical papers when compared to the simple counting of the published titles. Moreover, the described analysis of publications yields data which are useful in managing a research institution

    Effects of operation temperature on thermal expansion and main parameters of radial ball bearings

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    The research of influence of operation temperature on the thermal expansion and main parameters of radial ball bearings is presented in this paper. The main bearing parameters are identified in accordance with the increasing requests concerning stability and load capacity. A series of finite element analyses is performed for quasi-static analysis of all identified bearing parameters during contact period in referent temperature. Then, the dependence of bearing material characteristics on the operation temperature is discussed. Few series of finite element analyses are performed for a particular radial ball bearing type, with characteristics in accordance with manufacturer specifications, for several operation temperatures. These two problems analyses include consideration of relation between the initial radial clearance, thermal expansion strains, and contact deformations of the parts of the bearing assembly. The results for radial ball bearing parameters are monitored during a ball contact period for different temperatures and the appropriate discussion and conclusions are given. The conclusions about the contribution of developed procedure in defining the optimum operation temperature range are shown
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