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Validacija materialnega in poškodbenega modela za numerične simulacije termo-mehanskega utrujanja
Jure Vinkovič, 2019, diplomsko delo

Opis: Namen diplomskega dela je dokumentirati potek uporabe programa za validacijo materialnih in poškodbenih modelov za implementacijo le-teh pri numeričnih simulacijah termo-mehanskega utrujanja aluminijevih zlitin. Predstavljeno je teoretično ozadje utrujanja materiala, v katerega uvrščamo velikociklično, malociklično in termo-mehansko utrujanje materiala. Prav tako sta predstavljena viskoplastični materialni model in poškodbeni model, ki sta ključ za izračun končnega števila ciklov. Podane so osnovne mehanske in termične lastnosti ene izmed obravnavanih aluminijevih zlitin. Opisan je postopek pregleda rezultatov eksperimentalnih testov termo-mehanskega utrujanja aluminijevih zlitin, ki so bili izvedeni pri temperaturah do 320 °C. V zaključku diplomskega dela je predstavljen postopek uporabe programa AVL TMF TOOLBOX in skriptov, ki obdelajo in izpišejo podatke, ki so pomembni za validacijo materialnega in poškodbenega modela.
Ključne besede: termo-mehansko utrujanje, aluminijeve zlitine, validacija, materialni model, poškodbeni model, metoda končnih elementov
Objavljeno: 29.08.2019; Ogledov: 477; Prenosov: 0

Computational simulation of biaxial fatigue behaviour of lotus-type porous material
Janez Kramberger, Marko Šori, Matjaž Šraml, Srečko Glodež, 2016, izvirni znanstveni članek

Opis: A computational simulation of low-cycle fatigue behaviour of lotus-type porous material, subjected to biaxial in-phase loading cycles is presented in this paper. Fatigue properties of porous materials are less frequently published in the literature. This paper evaluates computational analyses, where different pore distribution and biaxial loading conditions in relation to the pore orientations is considered in each simulation. The fatigue analysis is performed by using a damage initiation and evolution law based on the inelastic strain energy. The computational results are subjected to the appropriate statistical analysis, because of different pore topology a different fatigue lives are obtained on the same loading level. Results of computational simulations show also a qualitative understanding of porosity influence on low-cycle fatigue failures of lotus-type porous material under biaxial loading conditions.
Ključne besede: Lotus-type porous material, low-cycle fatigue, damage, finite element analysis
Objavljeno: 02.08.2017; Ogledov: 553; Prenosov: 314
.pdf Celotno besedilo (1,08 MB)
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The influence of the morphology of iron powder particles on their compaction in an automatic die
Borivoj Šuštaršič, Matjaž Godec, Črtomir Donik, Irena Paulin, Srečko Glodež, Marko Šori, Milan Ratej, Nada Javornik, 2015, strokovni članek

Opis: Fe- and steel-based powder metallurgy (P/M) products, such as steel gears, spurs, locking mechanisms, porous filters, sliding bearings and bushes, as well as other machine parts and structural elements, are mainly produced with the so-called conventional sintering technology. It is the most efficient technology for the mass production of small, complex, functional and structural parts. Therefore, it is the most convenient and popular among all of the P/M technologies. The most important end-user of sintered parts is the automotive industry. However, small, complex, sintered parts can also be frequently used in the furniture and household industries, precise mechanics, articles for recreation and sports. A fine, iron-based powder mixture or prealloyed powder is first automatically uniaxial-die compacted (ADC) into the final shape of the product with a mechanical or hydraulic press and then sintered in a protective atmosphere at approximately 1100 °C. The metal powder mixture must have the appropriate engineering properties given by the chemistry and particle morphology, enabling a fast and reliable die-compaction process. The most important are a high tap density, a good powder flowability and a low compressibility. All this gives the green compacts an appropriate final shape with a smooth surface, a relatively high and uniform green density, as well as a green strength without internal flaws and cracks. In the case of very small two-or-more-heights products, for example, spur gears with a low module, it is very difficult to obtain a uniform green density at acceptable compaction pressures. Often small cracks are formed at height crossings and big differences in the green density appear in smaller or thinner regions. In the frame of our investigation we analysed the influence of the selected prealloyed commercial iron powder’s morphology and its technological properties on automatic die compaction, as well as the sintering process in the case of small two-level sintered gear dimensions of 5/40–7/10×7mm with module m = 0.5. The original iron powder was sieved and the finest powder particle fraction (< 45 µm) was compared with the original powder mixture considering ADC and sintering process. It was found that the selection of the finer powder mixture could not contribute to the improvement in the overall ADC process, as well as a better green compact. In the present paper the results of our investigations are presented and the reasons why a finer powder mixture cannot contribute much to an improvement of the conventional sintering process.
Ključne besede: Fe-based alloy powders, particles, morphology, microstructure, automatic die compaction, sintering
Objavljeno: 27.03.2017; Ogledov: 635; Prenosov: 275
.pdf Celotno besedilo (1,18 MB)
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Morphological and microstructural features of Al-based alloyed powders for powder-metallurgy applications
Borivoj Šuštaršič, Irena Paulin, Matjaž Godec, Srečko Glodež, Marko Šori, Jože Flašker, Albert Korošec, Stanislav Kores, Goran Abramović, 2014, strokovni članek

Opis: Besides advanced nano steels, polymers and ceramics, recently also light metals, i.e., Al, Mg and Ti based materials, have been recognized as future materials for different kinds of advanced applications. Al and its alloys have an acceptable price, excellent corrosive resistance, good mechanical and other physical properties. Therefore, they are also used in the powder-metallurgy (P/M) field. The P/M technology of Al materials is very demanding and has its own specifics compared to the sintering technology of iron and steel. A relatively large quantity of Al-based alloy powder is formed during the sand blasting of slugs and discs in the Talum Al factory, Kidričevo, Slovenia. Therefore, we analysed and investigated its practical usability for a production of advanced products using P/M technology. The formed Al-based powder was compared with the commercially available Al-based powders that are generally used for conventional sintering technology. In the first part of this paper we explain which types of Al-based powders are used for the production of sintered parts, what the required parameters are and why we considered them. Then, the results of theoretical thermodynamic analyses and investigations of the morphological and microstructural characteristics of the selected commercial Al-based powders are given, as well as their comparison with the Al powder formed during the sand blasting and its potential for P/M applications.
Ključne besede: Al-based alloy powders, morphology, microstructure, LM characterisation, SEM/EDS characterisation
Objavljeno: 17.03.2017; Ogledov: 796; Prenosov: 87
.pdf Celotno besedilo (4,85 MB)
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Material parameters for a numerical simulation of a compaction process for sintered double-height gears
Tomaž Verlak, Marko Šori, Srečko Glodež, 2015, strokovni članek

Opis: This paper presents the initial material parameters for the Ecka Alumix 231 aluminum-powdered metal required for a successful numerical simulation of a compaction process for sintered components with a proper software package. Experimental work was used to obtain Drucker-Prager-cap (DPC) model material parameters with the help of a Brazilian disc test and a uniaxial compression test for the linear part of the DPC model in the equivalent pressure stress/deviatoric stress (p-q) plane. The specimens used for this test were cylindrical probes (greens) that were compacted with a mechanical press and then compressed to the failure point in the axial and radial directions.
Ključne besede: aluminum-based powder, compaction process, Drucker-Prager cap model, numerical simulation, Ecka Alumix 231
Objavljeno: 16.03.2017; Ogledov: 781; Prenosov: 332
.pdf Celotno besedilo (864,37 KB)
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Fatigue properties of sintered DIN SINT-D30 powder metal before and after heat treatment
Marko Šori, Borivoj Šuštaršič, Srečko Glodež, 2014, izvirni znanstveni članek

Opis: The main focus of this study was to determine how heat treatment affects the dynamic properties of sintered steel. All the specimens were made of the DIN SINT-D30 metal powder, but only half of them were additionally heat treated. Flat specimens were cold pressed and sintered. The second set was additionally heat treated to increase the strength. After the static mechanical properties were determined, the fatigue strength was investigated in a pulsating machine with a load ratio of R = 0. Wöhler curves were plotted and the parameters for determining the fatigue life (of' and b) were calculated.
Ključne besede: powder metallurgy, fatigue, S-N curve
Objavljeno: 16.03.2017; Ogledov: 526; Prenosov: 78
.pdf Celotno besedilo (157,94 KB)
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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: 583; Prenosov: 66
.pdf Celotno besedilo (319,52 KB)
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Računski model za ugotavljanje upogibne trdnosti sintranih zobnikov
Marko Šori, 2015, doktorska disertacija

Opis: Metalurgija prahov je že dodobra uveljavljen proizvodni proces v industrijah z velikoserijsko proizvodnjo. V avtomobilski industriji so tako izdelani npr. različni manjši nosilci kompleksnih oblik, zobniki oljnih črpalk in njihova ohišja. Napredek tehnologije in materialov pa že nakazuje prodor kovinskih prahov tudi v bolj obremenjene avtomobilske dele; npr. ojnice in zobniki v menjalniku. Predlagan računski model izračuna upogibne trdnosti sintranih zobnikov temelji na dobrem poznavanju materialnih parametrov in geometrije obravnavanega zobnika. S klasičnim kvazistatičnim nateznim preizkusom so ugotovljene osnovne mehanske lastnosti materiala. Dinamičen odziv je ugotovljen glede na parametre Basquinove enačbe, ki so izračunani iz rezultatov testiranj pri utripni obremenitvi. Zaradi velike verjetnosti nastanka razpok med proizvodnim procesom je analiziran vpliv prisotnosti razpoke tako, da so določeni parametri Parisove enačbe, prag širjenja razpoke in lomna žilavost. Rezultati so pokazali izjemno pomembnost preprečevanja nastanka plastnih razpok, saj le-te kritično vplivajo na nosilnost sintranega izdelka. Tako kot običajno jeklo, se lahko tudi sintrano jeklo po sintranju še dodatno toplotno obdela z različnimi toplotnimi obdelavami, zato je vpliv poboljšanja, ki se navzven vidi kot sprememba mehanskih lastnosti materiala, preučen v analizi mikrostrukture. Računski model je predstavljen na primeru, ki implementira izmerjene materialne parametre in poznano geometrijo zobnika. Napetostno stanje v korenu zoba je z numeričnimi postopki ugotovljeno na podlagi geometrije in materialnih parametrov in se nato oplemeniti z izračunanimi parametri Basquinove enačbe do verjetnostne napovedi intervala, v katerem se pričakuje zlom zoba sintranega zobnika. Testiranje sintranih zobnikov na modificiranem FZG preizkuševališču pokaže, da predstavljen računski model ob znani geometriji in materialnih parametrih z natančnostjo velikostnega razreda napove dobo trajanja sintranega zobnika.
Ključne besede: metalurgija prahov, utrujanje, upogibna trdnost, sintrani zobniki
Objavljeno: 07.07.2015; Ogledov: 1772; Prenosov: 204
.pdf Celotno besedilo (8,81 MB)

Marko Šori, 2011, diplomsko delo

Opis: V diplomskem delu je predstavljeno dimenzioniranje polžnega gonila za pogon sledilnika sonca. V uvodnem delu je predstavljen problem z materialom polžnika in zastavljeni so cilji diplomskega dela. Sledita dve poglavji o teoretičnih osnovah polžnih dvojic. Najprej so predstavljene določilne veličine polžaste dvojice in preračun sil, kasneje pa še trdnostni preračuni glede na različne kriterije. V nadaljevanju je zasnova in preizkušanje prvih polžastih dvojic, kjer je ugotovljeno da je obstoječa geometrija načeloma neprimerna zaradi upogiba gredi polža, vendar se da problem rešiti z nitriranjem polžnika. Ker je postopek nitriranja za podjetje predrag je v naslednjem poglavju predstavljena geometrijsko drugačna polžasta dvojica, ki ima večjo upogibno togost in manjše upogibne sile. V analizi rezultatov je prikazana razlika koeficientov varnosti, kjer je razvidno, da se kljub dvakratnemu povečanju koeficienta varnosti proti upogibu gredi polža ostali koeficienti varnosti niso bistveno spremenili. V zaključku je ugotovljeno, da standard DIN 3996 ne predvideva jekel za poboljšanje kot materiala za polžnike in da ne podaja spodnje omejitve za ubirni kot.
Ključne besede: Polžaste dvojice, ozobljeni ležaji, pogon sledilnika sonca
Objavljeno: 13.10.2011; Ogledov: 2287; Prenosov: 253
.pdf Celotno besedilo (2,41 MB)

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