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Testiranje varjenih in ne varjenih prirobnic vodovodnih cevi
Žiga Šafar, 2015, undergraduate thesis

Abstract: Leteče prirobnice se v praksi uporabljajo za sestavljanje plastičnih cevovodov večjih premerov. Prirobnice morajo zagotoviti tesnenje pri določenih tlakih obratovanja. V tem delu smo se osredotočili na preizkušanje treh vrst letečih prirobnic, ki so se razlikovale po velikosti. Preizkušali smo dva tipa različnih prirobnic glede na način izdelave. Prve prirobnice so bile izdelane iz upognjenih trakov in varjene. Druge prirobnice so bile izrezane iz pločevine brez zvarih spojev. Preizkušanje prirobnic je potekalo s povečevanjem tlaka na prirobnične spoje. Pri preizkusu se je meril tlak preizkusnega medija in deformacije na kritičnih prerezih prirobnic. Deformacije so bile izmerjene z upornimi merilnimi lističi na mestu zvara in na mestu brez njega. Preizkusi so pokazali, da so opazne razlike pri deformiranju prirobnic na mestih, kjer imamo zvarni spoj v primerjavi z mestom, kjer ni zvarnega spoja. Preizkusili smo tudi prirobnične spoje z manjšim številom vijakov. V praksi se namreč dogaja, da v spoje ne vstavijo vseh vijakov. Ugotovili smo, da je tak spoj prirobnic vzdržal bistveno manjše obremenitve pred samo popustitvijo, tudi do štiri krat manj. Za natezne preizkuse pa so bili izdelani posebni preizkušanci, kjer se je preverila ustreznost nepopolno prevarjenega zvarnega spoja na varjenih prirobnicah.
Keywords: prirobnica, zvar, TVP, merjenje tlaka in deformacij
Published: 27.10.2015; Views: 771; Downloads: 28
.pdf Full text (9,84 MB)

3.
Microstructural changes during vacuum carburizing of steels
Mihael Brunčko, Ivan Anžel, Albert C. Kneissl, 2011, original scientific article

Published: 01.06.2012; Views: 647; Downloads: 56
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4.
Response of monocyte-derived dendritic cells to rapidly solidified nickel-titanium ribbons with shape memory properties
Sergej Tomić, Rebeka Rudolf, Mihael Brunčko, Ivan Anžel, V. Savić, Miodrag Čolić, 2012, original scientific article

Abstract: Ni-Ti Shape Memory Alloys (SMAs) have attracted considerable attention as biomaterials for medical devices. However, the biocompatibility of Ni-Ti SMAs is often unsatisfactory due to their poor surface structure. Here we prepared Rapidly Solidified (RS) Ni-Ti SMA ribbons by melt-spinning and their surface was characterised by Augerelectron spectroscopy, X-ray photoelectron spectrometry and scanning electron microscopy. The biocompatibility of the produced ribbons and their immunomodulatory properties were studied on human monocyte-derived dendritic cells (MoDCs). We showed that melt-spinning of Ni-Ti SMAs can form a thin homogenous oxide layer, which improves their corrosion resistance and subsequent toxicity to MoDCs. Ni-Ti RS ribbons stimulated the maturation of MoDCs, as detected by changes in the cells' morphology and increased expression of HLA-DR, CD86, CD40 and CD83 molecules. However, Ni-Ti RS ribbons enhanced the tolerogenic properties of immature MoDCs, which produced higher levels of IL-10 and IL-27, driving the differentiation of IL-10- and TGF-β-producing CD4+T cells. On the other hand, in the presence of lipopolysaccharide, an important pro-inflammatory biomolecule, Ni-Ti RS ribbons enhanced the allostimulatory and Th1 polarising capacity of MoDCs, whereas the production of Th2 and Th17 cytokines was down-regulated. In conclusion, Ni-Ti RS ribbons possess substantial immunomodulatory properties on MoDCs. These findings might be clinically relevant, because implanted Ni-Ti SMA devices can induce both desired and adverse effects on the immune system, depending on the microenvironmental stimuli.
Keywords: nickel-titanium alloy, biocompatibility, cytokines, immunomodulation, monocyte-derived dendritic cells
Published: 01.06.2012; Views: 945; Downloads: 203
.pdf Full text (1,35 MB)
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5.
In-situ monitoring of internal oxidation of dillute alloys
Mihael Brunčko, Ivan Anžel, Albert C. Kneissl, 2007, original scientific article

Abstract: This paper presents a non-destructive measurement method that enables identification and characterization of phenomena during internal oxidation of metallic materials as well as monitoring the kinetics of internal oxidation using "in-situ" electrical resistance measurements. A special laboratory device, based on the unique measurement cell, for the electrical resistance measurements at high temperatures and the model for electrical resistance transformation into an instantaneous microstructure were developed. To accomplish this, the process of internal oxidation was divided into the sequence of the key partial reactions that were presented in the model as the parallel andžor serial connected time variable resistors in the electrical circuit. The validity of the transformation model was experimentally confirmedby internal oxidation of Ag-Sn (2 at.% Sn) alloy at different oxidation temperatures in air atmosphere. The comparison of the results obtained by "in-situ" electrical resistance measurements with those obtained by metallographic analysis and Wagnerćs theory shows that the novel method presents a more effective tool for monitoring of internal oxidation kinetics. The method identifies also the microstructural defects and their influences onthe kinetics of internal oxidation.
Keywords: metallurgy, Ag-Sn alloy, internal oxidation, electrical resistance
Published: 01.06.2012; Views: 888; Downloads: 22
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6.
Monitoring of directional solidification with simultaneous measurements of electrical resistance and temperature
Mihael Brunčko, Ivan Anžel, Alojz Križman, 2003, original scientific article

Abstract: WE present the efficiency of simultaneous electrical resistance and temperature (ERT) measurements for monitoring the position, X, and the growth rate, V, of the solidification front during the directional solidification of alloys. On alaboratory device for directional solidification (Bridgman-type furnace), theeutectic Pb-Sn alloy was solidified at five different pulling rates, VP, with a constant imposed temperature gradient, GP. During directional solidification, the electrical resistance and the temperature changes were measured simultaneously in the experimental samples. The results of the experiments show that simultaneous measurement of ERT enables not only the determination of the average growth rate, V, during directional solidificationbut also its fluctuation over the total measurement length of the sample.
Keywords: metallurgy, Pb-Sn alloy, directional solidification, electrical resistance measurements, temperature measurements
Published: 01.06.2012; Views: 1025; Downloads: 68
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7.
Pregled merilnih metod za sprotno spremljanje usmerjenega strjevanja inženirskih materialov
Mihael Brunčko, Ivan Anžel, 2001, professional article

Abstract: Za dosego želenih fizikalnih in mehanskih lastnosti inženirskih materialov je ključnega pomena natančno spremljanje razvoja mikrostrukture pri izdelavi materialov. V prispevku je zbran pregled merilnih metod, s katerimi je mogoče kontrolirano spremljanje usmerjenega strjevanja. Predstavljene metode temeljijo na neporušnem in kontinuirnem ugotavljanju vrednosti vplivnih parametrov v bližini strjevalne fronte (▫$G_SF$▫ - temperaturni gradient na strjevalni fronti, ▫$V_SF$▫ - hitrost potovanja strjevanja fronte, ▫$deltaT_SF$▫ -podhladitev strjevalne fronte, ugotavljanje oblike stjevalne fronte) med samim usmerjenim strjevanjem in jih je mogoče uporabiti v raziskovalni in industrijski praksi.
Keywords: metalurgija, usmerjeno strjevanje, vplivni parametri strjevanja, merilne metode
Published: 01.06.2012; Views: 1000; Downloads: 61
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8.
Microstructural investigation of melt-spun NiTi based ribbons
Kambiz Mehrabi, Mihael Brunčko, Albert C. Kneissl, 2012, original scientific article

Abstract: In order to get small-dimensioned shape memory alloys (SMAs) with good functional and mechanical properties, a rapid solidification technique was employed. This paper discusses the use of different melt-spinning procedures for the preparation of proper thin NiTi ribbons. Metallographic characterization of SMAs is an important way to evaluate material properties, therefore the effect of alloy composition and different conditions of melt-spinning process (crucible, melting time and temperature) on the various inclusions and microstructure of NiTi alloys was investigated. Specimens for metallographic studies were cut from the longitudinal cross sections of melt-spun ribbons. The microstructures and different phases were examined by optical, scanning and transmission electron microscopy and the influence of the processing methods on microstructures of ribbons will be discussed.
Published: 10.07.2015; Views: 369; Downloads: 38
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9.
ŠTUDIJ VISOKOTEMPERATURNE OKSIDACIJE NERJAVNEGA JEKLA EN X12CR13 Z MERITVIJO ELEKTRIČNE UPORNOSTI
David Kolar, 2012, master's thesis

Abstract: V magistrski nalogi je opisan proces visokotemperaturne oksidacije jekla X12Cr13 v zračni atmosferi in pri mejnih temperaturah uporabnosti zasledovan z metodo sprotnega merjenja električne upornosti ter analiziran s karakterizacijo mikrostrukturnih sprememb, ki pri tem nastanejo. Z meritvijo električne upornosti smo določili kinetiko visokotemperaturne oksidacije pri različnih temperaturah in časih v zračni atmosferi. Za analizo nastalih oksidnih plasti smo uporabili metodi vrstične elektronske mikroskopije in Augerjeve elektronske spektroskopije. Rezultati raziskovalnega dela so pokazali, da kemijske reakcije in procesi, ki potekajo pri visokotemperaturni oksidaciji nerjavnih jekel, povzročijo zaznavne spremembe električne upornosti, ki jih lahko uporabimo za identifikacijo in določitev kinetike teh reakcij in procesov. S to metodo lahko tudi določimo čas do razpada zaščitnega oksidnega filma pri mejnih temperaturah uporabnosti jekla.
Keywords: visokotemperaturna oksidacija, nerjavna jekla, jeklo X12Cr13
Published: 23.10.2012; Views: 1317; Downloads: 330
.pdf Full text (2,19 MB)

10.
VPLIV EKSTREMNE PLASTIČNE DEFORMACIJE NA MIKROSTRUKTURO IN LASTNOSTI KOVINSKIH MATERIALOV
Matija Kos, 2014, doctoral dissertation

Abstract: V doktorski disertaciji je obravnavana problematika vpliva ekstremne plastične deformacije na mikrostrukturne spremembe disperzijsko utrjenega bakra, s ciljem, da se združi disperzijsko in deformacijsko utrjanje in ustvari nanostrukturni kompozit z izboljšanimi lastnostmi. V okviru doktorske disertacije je bila raziskana možnost doseganja velikih globin cone notranje oksidacije (CNO). Z modificiranim Rhinesovim paketom je bila dosežena zadostna globina cone notranje oksidacije za študij obnašanja disperzijsko utrjene zlitine med ECAP (Equal channel angular pressing) postopkom. Preučeno je bilo tečenje materiala na makro nivoju pri delno notranje oksidiranem preizkušancu in homogenem referenčnem vzorcu iz modelirne mase z namenom, da se ugotovi vpliv oksidnih delcev v CNO na tečenje materiala med ECAP postopkom in določi porazdelitev deformacije in stopnjo deformacijskega utrjanja po volumnu preizkušanca. Ugotovljeno je bilo, da na makroskopskem nivoju oksidni delci ne vplivajo na tečenje materiala, zato ni razlike v tečenju cone notranje oksidacije in trdne raztopine. S primerjavo razvoja mikrostrukture med ECAP postopkom v disperzijsko utrjenem materialu in trdni raztopini je bil ovrednoten vpliv oksidnih delcev na mehanizem plastične deformacije. Ugotovljeno je bilo, da oksidni delci povečajo fragmentacijo zrn med ekstremno plastično deformacijo, kar privede do nastanka nanometrskih enakoosnih zrn, ki so obdana z amorfnim mejnim področjem. Na osnovi rezultatov je bil postavljen model plastičnega tečenja nanostrukturnega kompozita v katerem se predpostavlja, da plastično tečenje poteka z drsenjem vzdolž mej zrn.
Keywords: ekstremna plastična deformacija, notranja oksidacija, nanostrukturni kompoziti, plastično tečenje.
Published: 04.03.2014; Views: 1276; Downloads: 139
.pdf Full text (7,60 MB)

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