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Modelling of unit differential reversal curves in the G2E hysteresis model
Ermin Rahmanović, Martin Petrun, 2024, izvirni znanstveni članek

Opis: Iron losses represent a crucial factor in the design process of electrical machines. For this reason, it is important to consider adequate hysteresis behavior within models which predict iron losses. A promising hysteresis description is the static hysteresis model developed by the G2Elab research group. It proposes a unique approach of modelling magnetization curves inside the major loop based on the so-called unit differential reversal curves (uDRCs). This work focuses on modelling of the uDRCs. We analyzed the accuracy and identification approaches of several uDRC models, where we compared the established model with simplified solutions with less parameters. Further, we analyzed the impact of individual models regarding identification convergence. Finally, we highlighted which simplified models give the best trade-off between the ease and stability of identification process of parameters, and the accuracy of the hysteresis model.
Ključne besede: static hysteresis model, iron loss, loss surface model, magnetic material, mathematical modelling
Objavljeno v DKUM: 26.01.2024; Ogledov: 83; Prenosov: 11
.htm Celotno besedilo (154,34 KB)

Reducing carbon footprint in an oem supply chain caused by inadequate interpretation of x-ray results of hidden defects in ductile iron castings
Tadej Pavlin, Iztok Brinovar, Bojan Stergar, Zdravko Praunseis, 2022, izvirni znanstveni članek

Opis: In the global market, the casting industry recorded a growth trend for ductile iron last year. Ductile iron is used due to its excellent mechanical properties, machinability and castability. The microstructure of nodular cast iron consists of a metal matrix and graphite extruded in the form of beads and nodules. In recent years, the production of ductile iron castings has increased significantly for parts for heavy transport vehicles and containers for permanent disposal of nuclear waste, and it is expected that this trend of expansion will continue for at least the next twenty years. When poured in sand moulds, the quality of products can not be reached. There can be defects on the raw surface and/or on the machining surface, as well as hidden defects inside the material. For casting products, defects can be detected on raw and machining surfaces and inside material defects by carrying out a visual inspection. The results of the inspection depend on the inspection method used. In general, basic methods of cutting or milling inspection are used in the casting industry, which means that products are classified in terms of whether or not they meet the drawing specification(s). The authors of this paper focused on the hidden defects inside ductile iron material, which can be detected by carrying out a cutting or milling inspection or through an X-ray inspection. Huge amounts of energy and energy sources are used in the production of nodular cast iron, which creates a negative environmental footprint. Therefore, by being preventively rational and through appropriate control procedures it is possible to significantly reduce the carbon footprint.
Ključne besede: carbon footprint, ductile iron, X-ray inspection, cutting inspection, hidden mistakes, defects, porosity, inclusion, green energy, reduced production of energy, decrease in production emissions
Objavljeno v DKUM: 26.10.2023; Ogledov: 202; Prenosov: 4
.pdf Celotno besedilo (5,27 MB)
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Comparison and implementation of thermo-mechanical fatigue damage models : magistrsko delo
Jure Vinkovič, 2021, magistrsko delo

Opis: The basis of the master thesis is an in-depth and comprehensive analysis of the scientific literature on damage models of thermo-mechanical fatigue. The aim of the thesis is to investigate and determine the suitability of damage models for their application in numerical simulations of components subjected to thermo-mechanical loading with in-phase, out-of-phase or constant temperature cycles. The theoretical background of material behavior under static and dynamic loads (e.g. low-cycle fatigue, high-cycle fatigue) is presented. The work also includes an overview of damage mechanisms typical of time-temperature varying loading conditions (e.g. cyclic softening and hardening of the material, mean stress relaxation, material creep, visco-plasticity, etc.). This is followed by a structured review of several damage models of thermo-mechanical fatigue (e.g. Neu-Sehitoglu, DTMF, Coffin-Manson, Ostergren, Smith-Watson-Topper, Unified Energy Approach, etc.). An overview of the experimental tests on aluminum alloy and cast iron carried out at temperatures up to 800 °C is given. The idea of processing the raw experimental data including the calibration procedure of the thermo-mechanical fatigue damage models is schematically illustrated and described. The basic mathematical laws of constitutive material models for both material types are given. In the conclusion of the MSc thesis, the correlations of the calibrated damage models are presented, which, together with the constructive opinions, give an important message on the application of the individual damage models depending on the type of material and the loading method.
Ključne besede: thermo-mechanical fatigue, constitutive material model, damage model, aluminum alloy, cast iron alloy, finite element method
Objavljeno v DKUM: 03.01.2022; Ogledov: 764; Prenosov: 0

Reactive sintering of $MnZn$ ferrites
Tomaž Kosmač, Mihael Drofenik, 2001, izvirni znanstveni članek

Opis: Reaction-formed $MnZn$ ferrite was prepared and the decrease in shrinkage after sintering due to the volume expansion accompanying iron oxidation was studied. Green compacts consisting of the milled raw oxides $Fe_2O_3$, $Mn_3O_4$, $ZnO$ and metallic iron powder were sintered at 1350 °C in air. During the first hold at 800 °C, $Fe$ was oxidized to $\alpha-Fe_2O_3$ and $Zn$ ferrite was formed. Above 1300 °C the reaction bonding was completed and $MnZn$ ferrite, exhibiting a relatively low shrinkage, was formed. The chemical reactions involved during reaction bonding were associated with a volume expansion and porosity formation, compensating for the shrinkage on sintering. Intensive milling decreases the porosity after sintering but induces the oxidation of iron, and partially removes the shrinkage compensation caused by the presence of metallic iron.
Ključne besede: reaction-forming, $MnZn$ ferrite, inorganic technology, ferrite ceramics, reaction bonded ceramics, sintering, iron oxides, iron
Objavljeno v DKUM: 25.08.2017; Ogledov: 1040; Prenosov: 105
.pdf Celotno besedilo (441,54 KB)
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The characterisation of nanosized nickel-zinc ferrites synthesized within reverse micelles of CTAB/1-hexanol/water microemulsion
Vuk Uskoković, Mihael Drofenik, Irena Ban, 2004, izvirni znanstveni članek

Opis: Stoichiometric nanocrystalline nickel-zinc ferrites were synthesized by a reverse micelle method following a multi-microemulsion approach. Different pH values were chosen for the alkali precipitating reaction during the synthesis of different powders. Synthesized, as-dried and subsequently calcined powders were characterized in terms of their magnetic properties. XRD analyses and specific-surface area measurements were used to determine the average particlesizes of the synthesized samples. DCS and TGA measurements were performed to reveal the phase transitions within the samples at elevated temperatures, whereas TEM was used to view and record the microstructure of the nanosized ferrite samples. A possible mechanism of the formation of the synthesized NiZn-ferrite was also discussed.
Ključne besede: magnetic materials, magnetic nanoparticles, microemulsion synthesis, nickel, iron, fine powders, Ni-Zn ferrites, reverse micelle method
Objavljeno v DKUM: 01.06.2012; Ogledov: 1908; Prenosov: 52
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Crystal-structure and Mössbauer studies of Li[sub]1.746]Nd[sub]4.494FeO9[sub]9.493
Mihael Drofenik, Irena Ban, Darko Makovec, Darko Hanžel, Amalija Golobič, Ljubo Golič, 2007, izvirni znanstveni članek

Opis: The ▫$Li_1.746Nd_4.494FeO_9.493$▫ (LNF) ternary phase, located in the ▫$Li_2O$▫-rich part of the ▫$Li_2O-Nd_2O_3-Fe_2O_3$▫ system, crystallizes with a cubic unit cell of dimension and the space group Im3m. Refinement on F resulted in R=1.9%. The structure is comprised of a network of corners, edges and faces sharing the coordination polyhedra of neodymium. In between this skeleton the regular octahedra of oxygen-coordinated iron and trigonal prisms of lithium are located. The Mössbauer spectra revealed the presence of ▫$Fe^3+$▫, ▫$Fe^4+$▫ and ▫$Fe^5+$▫ ions distributed on two symmetry-independent lattice positions.
Ključne besede: crystal structure, ternary compounds, single-crystal X-ray diffraction, Mössbauer spectroscopy, iron oxidation state, kristalna struktura, ternarne spojine, rentgenska difrakcija, Mössbauerjeva spektroskopija, rentgenska strukturna analiza
Objavljeno v DKUM: 01.06.2012; Ogledov: 2426; Prenosov: 46
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Additive fabrication in metallurgy - case study of grey cast iron valve production
Bogdan Valentan, Igor Drstvenšek, Tomaž Brajlih, Peter Sever, Simon Brezovnik, Jože Balič, 2010, strokovni članek

Opis: Additive Fabrication technologies are well known from the last two decades. In that time Additive Fabrication technologies have evolved from strictly prototype part production into an option that can also be used to produce end-user parts. With development of Additive Fabrication machines capable of producing metal parts, a complete substitution of conventional metal casting technologies is possible. However, direct Additive Fabrication of metal parts is still not time/cost effective when producing large volume parts, and nowadays there is still lack of materials that can be used on those machines. This paper presents a method how a conventional sand casting process can be assisted by Additive Fabrication technologies. A sand mould pattern is produced by Selective Laser Sintering. Additive Fabrication is also used in direct manufacturing of cores.
Ključne besede: gray cast iron, layered technologies, rapid prototyping, rapid manufacturing, sand casting
Objavljeno v DKUM: 31.05.2012; Ogledov: 2113; Prenosov: 22
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Dynamic two-axis model of a linear synchronous reluctance motor based on current and position-dependent characteristics of flux linkages
Gorazd Štumberger, Bojan Štumberger, Drago Dolinar, 2006, izvirni znanstveni članek

Opis: This paper analyses the impact of armature slotting and magnetically nonlinearand anisotropic iron core on the trajectories of a kinematically controlled linear synchronous reluctance motor (LSRM). A new magnetically nonlinear dynamic two-axis LSRM model is introduced in order to perform the analysis. The magnetic nonlinearities and slotting effects are accounted for by the current and position-dependent characteristics of flux linkages.
Ključne besede: devices motors, reluctance synchronous motor, iron core model
Objavljeno v DKUM: 31.05.2012; Ogledov: 2503; Prenosov: 104
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The synthesis of iron-nickel alloy nanoparticles using a reverse micelle technique
Irena Ban, Mihael Drofenik, Darko Makovec, 2006, izvirni znanstveni članek

Opis: Nanosized Fe0.2Ni0.8 particles were prepared by reducing their salts with sodium borohydride (NaBH4) in cationic water-in-oil (w/o) microemulsions of water/cetyl-trimethyl-amonium bromide (CTAB) and n-butanol/isooctane at 25 °C.According to the TEM and X-ray diffraction analyses, the synthesized particles were around 4-12 nm in size. Due to their nanodimensions, the particles had a primitive cubic (pc) structure rather than the body-centered cubic (BCC) structure of the bulk material. An examination of the synthesis from the reverse micelle reveals that the morphology of the iron-nickel alloy nanoparticles depends mainly on the microemulsion`s composition. The magnetization of the nanoparticles was much lower than that of the bulk material, reflecting the influence of the nanodimensions on the particlesć magnetizations.
Ključne besede: magnetic materials, nickel/iron alloys, nanoparticles, synthesis, microemulsions, magnetic properties, reverse micelles
Objavljeno v DKUM: 31.05.2012; Ogledov: 2000; Prenosov: 105
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