Iskanje po katalogu digitalne knjižnice

Opis: V magistrski nalogi smo obravnavali problematiko votline, ki je posledica nekovinskega vključka ali pore in razpoke v elementu. Obravnavali smo več različnih primerov, ki so imeli različne geometrijske kombinacije velikosti in lokacije votline, okrog katere je nastala razpoka. S pomočjo numeričnih simulacij smo ugotavljali, kakšna je razlika v enako veliki razpoki, ki je nastala iz votline, od ravninske do v materialu zajete razpoke. Razliko smo ugotavljali na osnovi numeričnih simulacij modela iz končnih elementov, na osnovi izračuna faktorja intenzitete napetosti vzdolž konture razpoke. Ugotovili smo, da pri kratkih razpokah, ki so nastale iz votline v materialu, so vrednosti faktorja intenzitete napetosti manjše, kot to velja za enako veliko ravninsko razpoko v notranjosti materiala. Rezultati so pomembni zaradi določanja relevantne vrednosti faktorja intenzitete napetosti po konturi razpoke, ki je nastala iz vključka, za določitev trajne dinamične trdnosti materiala.
Ključne besede: Faktor intenzitete napetosti, razpoke, nekovinski vključki, pore, numerične simulacije, analitični preračuni
Objavljeno v DKUM: 04.09.2024; Ogledov: 69; Prenosov: 16
Celotno besedilo (10,35 MB)

Opis: When manufacturing complicated products where both material and design play a role, especially thin and curved components, it is difcult to maintain accurate dimensions in Selective Laser Melting. Considering these difculties, this article presents the dimensional errors in the fabrication of Ti-6Al-4V discs and their thermomechanics during manufacturing. Various combinations of laser processing parameters were used to fabricate the 2.00 mm thick discs with a diameter of 5.70 mm. It was found that the thickness shortened and the round shape changed to an oval shape for most of the discs. The thickness decreased along the build-up direction from the bottom to the top and formed a taper that increased with increasing energy density (ED). The horizontal diameter of the discs changed slightly, while the vertical diameters changed remarkably with increasing ED. On the other hand, reducing the laser power resulted in a reduction of the roundness error, while it caused a reduction of the thickness. The hatch spacing signifcantly afected the volume of the melt pool and caused a change in the vertical diameter. The central part of the curved surface of the discs became concave and the concavity increased due to the increasing ED.
Ključne besede: dimension, Ti-6Al-4V, lase power, scanning speed, hatch spacing, selective laser melting
Objavljeno v DKUM: 29.03.2024; Ogledov: 219; Prenosov: 9
Celotno besedilo (4,48 MB)
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Opis: This study analyzed the fatigue failure of a parabolic spring made of 51CrV4 steel. A fracture mechanics approach was used to quantify the driving force and resistance for different loading configurations, inclusion sizes, and residual stresses. The analysis considered surface and internal initiation processes, including the impact of residual stresses introduced by shot peening. Key findings include the ability of the methodology to analyze the variables influencing fatigue resistance and failure configuration, the competition between surface and internal fracture processes, the limitation of residual stresses, the importance of minimizing the maximum inclusion size, and the potential for enhancing the propagation threshold for long cracks. The employed methodology facilitates not only the quantification but also the comprehension of the influence of the intrinsic material resistance on the fracture process.
Ključne besede: spring, fracture mechanics, short cracks, fatigue strenght estimation, small defect assessment
Objavljeno v DKUM: 26.03.2024; Ogledov: 189; Prenosov: 18
Celotno besedilo (3,99 MB)
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Opis: Porosity in sintered materials negatively affects its fatigue properties. In investigating its influence, the application of numerical simulations reduces experimental testing, but they are computationally very expensive. In this work, the application of a relatively simple numerical phase-field (PF) model for fatigue fracture is proposed for estimation of the fatigue life of sintered steels by analysis of microcrack evolution. A model for brittle fracture and a new cycle skipping algorithm are used to reduce computational costs. A multiphase sintered steel, consisting of bainite and ferrite, is examined. Detailed finite element models of the microstructure are generated from high-resolution metallography images. Microstructural elastic material parameters are obtained using instrumented indentation, while fracture model parameters are estimated from experimental S–N curves. Numerical results obtained for monotonous and fatigue fracture are compared with data from experimental measurements. The proposed methodology is able to capture some important fracture phenomena in the considered material, such as the initiation of the first damage in the microstructure, the forming of larger cracks at the macroscopic level, and the total life in a high cycle fatigue regime. However, due to the adopted simplifications, the model is not suitable for predicting accurate and realistic crack patterns of microcracks.
Ključne besede: sintered steel, microcracks, fatigue, phase-field method, porosity
Objavljeno v DKUM: 09.02.2024; Ogledov: 349; Prenosov: 18
Celotno besedilo (8,81 MB)
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Opis: V diplomski nalogi bo predstavljeno parametrično modeliranje vrtljive mize polnilnega stroja v podjetju GEA Vipoll d.o.o. Kjer se ukvarjajo z izdelavo polnilnih linij za živilsko in prehrambeno industrijo, ki velja za eno pomembnejših industrij sveta. Predstavljena bo tudi polnilna linija na splošno in parametrično modeliranje, ki sem ga uporabil za modeliranje vrtljive mize. Celoten model in tudi tehnična dokumentacija sta bila narejena v paketu SolidWorks.
Ključne besede: vrtljiva miza, parametrično modeliranje, polnilni stroj
Objavljeno v DKUM: 22.01.2024; Ogledov: 353; Prenosov: 50
Celotno besedilo (2,27 MB)