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1.
A new method for estimating the Hurst exponent H for 3D objects
Matej Babič, Peter Kokol, Nikola Guid, Peter Panjan, 2014, izvirni znanstveni članek

Opis: Mathematics and computer science are very useful in many other sciences. We use a mathematical method, fractal geometry, in engineering, specifically in laser techniques. Characterization of the surface and the interfacial morphology of robot-laser-hardened material is crucial to understand its properties. The surface microstructure of robot-laser-hardened material is rough. We aimed to estimate its surface roughness using the Hurst parameter H, which is directly related to the fractal dimension. We researched how the parameters of the robot-laser cell impact on the surface roughness of the hardened specimen. The Hurst exponent is understood as the correlation between the random steps X1 and X2, which are followed by time for the time difference t. In our research we understood the Hurst exponent H to be the correlation between the random steps X1 and X2, which are followed by the space for the space difference d. We also have a space component. We made test patterns of a standard label on the point robot-laser-hardened materials of DIN standard GGG 60, GGG 60 L, GGG 70, GGG 70 L and 1.7225. We wanted to know how the temperature of point robot-laser hardening impacts on the surface roughness. We developed a new method to estimate the Hurst exponent H of a 3D-object. This method we use to calculate the fractal dimension of a 3D-object with the equation D = 3 - H.
Ključne besede: fractal structure, Hurst exponent, robot, hardening, laser
Objavljeno: 14.03.2017; Ogledov: 491; Prenosov: 57
.pdf Celotno besedilo (468,97 KB)
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2.
Ugotavljanje poškodb vrvnih prižemk in analiza vzrokov njihovega nastanka
Žiga Bajt, Viljem Kuhar, Andraž Legat, Mirjam Bajt Leban, Janez Gomboc, 2001, strokovni članek

Opis: Vrvna prižemka je nosilni, dinamično obremenjen konstrukcijski element, ki povezuje sedežno obešalo s transportno vrvjo sedežnice. V lanskem letu smo sistematično vizuelno in defektoskopsko pregledali večje število prižemk in ostalih vitalnih konstrukcijskih elementov sedežnic. Osnovni cilj preiskav je bil oceniti njihovo stanje, detektirati obstoječe razpoke in ostale poškodbe, ki bi lahko vodile do nenadnih lomov ter določili obseg teh poškodb. Ultrazvočna metoda s posebej prirejeno površinsko sondo se je pokazala kot najprimernejša in izredno zanesljiva metoda za določanje razpok na prižemkah. Rezultati preiskav so pokazali, da ima material prižemk in nekaterih drugih konstrukcijskih elementov zelo nizko žilavost in grobo zrnato feritno - perlitno mikrostrukturo, ki je posledica neustrezne toplotne obdelave. Konstrukcijski elementi iz materiala s tako strukturo ne zagotavljajo zadostne odpornosti proti krhkemu lomu.
Ključne besede: žilavost, strojništvo, utrujenostne razpoke, metalurgija, ogljično jeklo, prižemke, ultrazvočna preiskava
Objavljeno: 14.03.2017; Ogledov: 286; Prenosov: 22
.pdf Celotno besedilo (126,46 KB)
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3.
Ocenitev občutljivosti na razpokljivost v hladnem pri varjenju visokotrdnostnega jekla Niomol 490 K
Zdravko Praunseis, Vladimir Gliha, Inoslav Rak, 2000, izvirni znanstveni članek

Opis: V članku je predstavljena analitična (z empiričnimi enačbami) in eksperimentalna (z Y-preizkusom) določitev temperature predgrevanja visokotrdnostnega jekla Niomol 490 K debeline 19 mm, pri kateri ne bo prišlo do pojava razpok v hladnem v zvarnem spoju. Ugotovljeno je, da je pri varjenju jekla Niomol 490 K z oplaščeno elektrodo EVB NiMo nastanku razpok v hladnem bolj podvržen var kot osnovni material. Z izračuni lahko dovolj natančno napovemo temperaturo predgrevanja jekla, vendar je treba dokazati temperaturo predgrevanja tudi z Y-preizkusom.
Ključne besede: visokotrdnostno jeklo, razpokljivost v hladnem, Y-preizkus, temperatura predgrevanja
Objavljeno: 01.06.2012; Ogledov: 1232; Prenosov: 54
.pdf Celotno besedilo (756,66 KB)
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4.
Upogibna trdnost korundne keramike
Milan Ambrožič, Lovro Gorjan, 2012, strokovni članek

Opis: Statistično smo ovrednotili 5100 eksperimentalnih vrednosti upogibnih trdnosti testnih vzorcev iz redne proizvodnje korundnih keramičnih izdelkov. Primerjali smo teoretično izračunano Weibullovo porazdelitev z dvema drugima pogosto uporabljenima dvoparametričnima porazdelitvama, normalno in log-normalno, da bi ugotovili, katera se najbolj sklada z meritvami. Za izračun ustreznih prostih parametrov smo uporabili metodo največje verjetnosti (maximum-likelihood method). Potem smo za primerjavo rezultatov uporabili Q–Q-diagrame. Potrdili smo domnevo, da se z eksperimentalnimi vrednostmi trdnosti najbolj ujema Weibullova porazdelitev.
Ključne besede: upogibna trdnost, Weibullova porazdelitev, statistične metode
Objavljeno: 14.03.2017; Ogledov: 313; Prenosov: 40
.pdf Celotno besedilo (238,17 KB)
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5.
Binding silver nano-particles onto viscose non-woven using different commercial sol-gel procedures
Tanja Pivec, Zdenka Peršin, Silvo Hribernik, Tina Maver, Mitja Kolar, Karin Stana-Kleinschek, 2012, izvirni znanstveni članek

Opis: The paper presents possible solution of Ag binding using commercial sol-gel systems which enable its low release into a wound, providing a good antimicrobial effect on those bacterial cultures that are most likely present in the wound. The influence of different sol-gel systems on the hydrophilic properties of carrier materials and the level of released silver has been studied. The results showed that sol-gel as binding-systems could provide proper hydrophilic properties of material, whilst binding silver strongly enough providing at the same time excellent antimicrobial activity of the treated viscose meterials.
Ključne besede: silver nano-particles, sol-gel, viscose non-woven, silver release, hydrophilicity, antimicrobial properties
Objavljeno: 01.06.2012; Ogledov: 1945; Prenosov: 39
.pdf Celotno besedilo (235,88 KB)
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6.
CFD analysis of exothermic reactions in Al-Au nano multi-layered foils
Karlo Raić, Rebeka Rudolf, Primož Ternik, Zoran Žunič, Vojkan Lazić, Dragoslav Stamenković, Tatjana Tanasković, Ivan Anžel, 2011, izvirni znanstveni članek

Opis: This work presents the possibility of numerical modelling using Computational Fluid Dynamics (CFD) in the field of nano-foils. The governing equations were solved using a Finite Volume Methodology (FVM). The computational domain was discretized using a uniform Cartesian grid with the appropriate mesh size along the x and y directions employing the corresponding number of grid points. The field variables were discretized at the cell centres and the spatial, as well as the time, derivatives were approximated using the second-order accurate numerical scheme. The time-evolution of the temperature and concentration fields, as well as the atomic diffusion coefficient, will be presented for the appropriate Al-Au nano-foil geometry and boundary conditions.
Ključne besede: Au-Al nano-foils, finite volume method, temperature transfer, concentration transfer
Objavljeno: 01.06.2012; Ogledov: 972; Prenosov: 56
.pdf Celotno besedilo (526,41 KB)
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7.
Characterization of heterogeneous arc welds through miniature tensile testing and Vickers-hardness mapping
Stjin Hertelé, Jonas Bally, Nenad Gubeljak, Primož Štefane, Patricia Verleysen, Wim De Waele, 2016, izvirni znanstveni članek

Opis: The heterogeneity of arc-welded connections is often ignored in structural assessments, giving rise to inaccuracies. Improved assessments taking into account heterogeneity require the characterization of local constitutive properties. We have compared two methods to do this: Vickers-hardness mapping and miniature tensile testing. Whereas the former is more straightforward to apply, the latter provides full-range stress-strain data. This paper discusses an experimental comparison of both methods on a heterogeneous arc weld. Miniature tensile tests were performed, using digital image correlation to measure the strain. The specimens were indented to compare their stress-strain response with Vickers hardness. Notwithstanding that small natural flaws invalidated some tests, reliable stress-strain curves were obtained. Vickers hardness testing is a convenient alternative if the yield and ultimate tensile strength are the only points of interest and the corresponding conversion inaccuracy is acceptable.
Ključne besede: arc weld, heterogeneity, hardness, miniature tensile testing, digital image correlation
Objavljeno: 14.03.2017; Ogledov: 355; Prenosov: 185
.pdf Celotno besedilo (797,43 KB)
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8.
Continuous vertical casting of a NiTi alloy
Aleš Stambolić, Ivan Anžel, Gorazd Lojen, Aleksandra Kocijan, Monika Jenko, Rebeka Rudolf, 2016, izvirni znanstveni članek

Opis: In this paper we present research that is connected to the performance of a series of experiments combined with the vacuum-induction melting and continuous vertical casting of a NiTi alloy in order to produce the strand. The theoretical chosen parameters made it possible to obtain a continuously cast strand with a diameter of 11 mm. The strand microstructures were investigated with a light and scanning electron microscope, while the chemical composition of the single phase was identified with the semi-quantitative micro-analysis energy-dispersive X-ray spectroscopy and inductively coupled plasma – optical emission spectrometry. The research showed that the microstructure is dendritic, where in the inter-dendritic region the eutectic is composed of a dark NiTi phase and a bright TiNi3–x phase. In some areas we found Ti carbides and phases rich in Fe. The micro-chemical analysis of the NiTi strand showed that the composition changed over the cross and longitudinal sections, which is proof that the as-cast alloys are inhomogeneous. In the final part, the electrochemical behaviours of NiTi strand samples were compared to a commercially available NiTi cast alloy with the same composition.
Ključne besede: NiTi alloy, continuous vertical casting, microstructure, potentiodynamic and impedance test
Objavljeno: 14.03.2017; Ogledov: 546; Prenosov: 164
.pdf Celotno besedilo (586,88 KB)
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9.
Določevanje hitrosti širjenja utrujenostne razpoke v zvarnem spoju pri majhnih prirastkih
Jožef Predan, Nenad Gubeljak, Maks Oblak, Janko Legat, 2002, izvirni znanstveni članek

Opis: Standardi in dokumenti za določitev hitrosti širjenja razpoke predvidevajo uporabo standardnih preizkušancev, na katerih je mogoče meriti dolžino razpoke od nekaj deset do nekaj sto milimetrov prirastka. Problem postaja težaven pri zvarnih spojih, kadar se merijo prirastki razpoke na skupni razdaljile nekaj milimetrov. Za to so poglavitni razlogi naslednji: utrujanje poteka z relativno nizko amplitudo faktorja intenzitete napetosti v področju utrujenostnega praga, mikro strukturna in trdnostna heterogenost zvarnega spoja, zaostale napetosti kot posledica varjenja, med utrujanjem se način odpiranja razpoke lokalno spreminja iz enoosno nateznega na ravninsko strižno in nasprotno. Omenjeni dejavniki se kažejo z izrazito neurejeno sliko hitrosti širjenja utrujenostne razpoke. V prispevku je opisan postopek za predobdelavo eksperimentalno izmerjenih vrednosti (prirastek razpoke, št. nihajev), ki omogoča zanesljivejšo določitev hitrosti širjenja utrujenostne razpoke v zvarnem spoju za majhne prirastke do zloma, ko faktor intenzitete napetosti preseže lomno žilavost.
Ključne besede: zvarni spoji, utrujenostna razpoka, faktor intenzivnosti napetosti, prag
Objavljeno: 01.06.2012; Ogledov: 1281; Prenosov: 66
.pdf Celotno besedilo (186,33 KB)
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10.
DSC/TG of Al-based alloyed powders for p/m applications
Borivoj Šuštaršič, Jože Medved, Srečko Glodež, Marko Šori, Albert Korošec, 2014, izvirni znanstveni članek

Opis: Al-based alloyed powders, appropriate for the sintering procedure (powder metallurgy, P/M) contain the alloying elements with a high solid solubility in Al, enabling reaction and liquid-phase sintering. They are surface oxidised because of a high affinity of Al to oxygen. Besides, this type of powders contains a polymeric lubricant (wax), which reduces the friction on die walls during automatic die compaction into the final compact shape of a product. This lubricant has to be removed slowly during the first stage of sintering in order to prevent deformations and cracking of the product. Consequently, its sintering is very complex. Generally, these powders are sintered in pure nitrogen with a low dew point. The optimum sintering conditions are generally determined on the basis of light and scanning electron microscopy. The investigation can also be completed very successively with differential scanning calorimetry and thermo gravimetry. The first one allows an insight into the endo- and exothermic reactions, taking place during the heating and cooling of a compacted metal powder, and the second one allows an insight into the processes, connected with the mass loss (a reduction, a lubricant removal, etc.) or mass increase (an oxidation). The DSC/TG of three commercial Al-based alloyed powders was performed in the frame of our investigations. The results were compared with the theoretical thermodynamic-based calculations and the optimum sintering conditions were proposed.
Ključne besede: aluminium powders, sintering, differential scanning calorimetry and thermo gravimetry
Objavljeno: 15.03.2017; Ogledov: 352; Prenosov: 32
.pdf Celotno besedilo (319,52 KB)
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