1. KARAKTERIZACIJA NEOKSIDIRANEGA DELA NOTRANJE OKSIDIRANE BAKER ALUMINIJEVE ZLITINE PREOBLIKOVANE PO ECAP POSTOPKU IN PREUČITEV POSTOPKA Z VIDIKA DIFUZIJE INOVACIJPeter Kirbiš, 2011, diplomsko delo Opis: Današnje inženirstvo napreduje, proti novim tehnologijam materialov, kar odpre nove konstrukcijske možnosti zmanjševanja presekov, vztrajnostnih mas in dimenzij izdelkov. Vse izrazitejše se kažejo potrebe po uporabi, naprednih materialov z specifičnimi lastnostmi, kot so visoka trdnost in trdota, izboljšana žilavost, odpornost na ciklično utrujanje, povečana električna in toplotna prevodnost, ter toplotna obstojnost.
Proizvodnja takšnih materialov, zahteva nove proizvodnje tehnologije, in uporabo vseh dosedanjih znanj iz področja materialov. Lastnosti materiala, lahko izboljšamo na različne načine, osredotočili se bomo predvsem na zmanjševanje velikosti kristalnih zrn in vnašanje drobnih delcev v mikrostrukturo. Z zmanjšanjem velikosti kristalnih zrn, dosežemo večje napetosti tečenja, v skladu z Hall-Petchovo odvisnostjo. Ko se zmanjša velikosti zrn pod 1µm, imamo opravka z materiali, ki imajo, nove edinstvene kombinacije lastnosti. Študij literature je pokazal, da je mogoče doseči submikronsko, in celo nanokristalno mikrostrukturo, z aplikacijo velikih plastičnih deformacij. To dosežemo z izpostavljanjem materiala velikim tlakom, torziji oz. enostavnemu strigu. Eden najbolj obetavnih postopkov z tega področja, je tako imenovan ECAP postopek, pri katerem je prisotna možnost uporabe v industrijski praksi, ki bo preučena v tej publikaciji. Ključne besede: Tehnologije materialov, inovacijski manegement, ecap(equal channel angular presing), spd (severe plastic deformation), notranja oksidacija, karakterizacija cu-al zlitine, nanokristalne kovine, mehanske lastnosti, utrjevalni mehanizmi, hall-petch-ova enačba, proizvodnja nanokristalnih kovin, karakterizacija nanokovin, optični mikroskop, sem (rasterski elektronski mikroskop), tem (presevni elektronski mikroskop), ebsd( sipanje povratnih elektronov), ecap izvedbe, priprav vzorcev za rastersko Objavljeno: 13.10.2011; Ogledov: 1453; Prenosov: 122 Polno besedilo (2,63 MB) |
2. Modern deformation measurement techniques and their comparisonBoštjan Kovačič, Rok Kamnik, Miroslav Premrov, Nenad Gubeljak, Jožef Predan, Zdravko Tišma, 2008, pregledni znanstveni članek Opis: Deformation measurement experiment has been undertaken where a concrete structure was subject to controlled loading. Concrete plate was loaded with hydraulic cylinder PZ 100 up to 42 kN. Nikon total station ser. 720 and camera Fuji Pro S3 have been used to make measurements at critical points during each additional load. A hydraulic computer operated cylinder was used for load increase. The use of total stations for deformation measurements is quite often, but the combination with digital photography is rather new and very suitable technique. It offers the capability of simultaneous monitoring of a large number of signalized or non-signalized points with very low root mean square error of 0.16 mm in geodetic method 0.7 mm in photogrammetry, respectively. The concrete plate was modeled and the comparison with the geodetic, photogrammetric and hydraulic method was made. Ključne besede: deformation measurements, geodesy, digital photogrammetry Objavljeno: 31.05.2012; Ogledov: 914; Prenosov: 12 Polno besedilo (0,00 KB) |
3. Characterization of open-cell cellular material structures with pore fillersMatej Vesenjak, Andreas Öchsner, Zoran Ren, 2008, izvirni znanstveni članek Opis: Due to their mechanical properties, cellular material structures are often used in automotive, aerospace, ship and railway industries, as elements for deformational energy absorption. New advanced cellular material structures have been evaluated and characterised in the scope of this study in order to determine their energy absorption capability through the deformation process. Parametric computational simulations in the framework of the finite element method have been used for this purpose. Newly developed computational models of regular open-cell cellular material structures considering viscous pore fillers have been developed and their response under impact conditions was analysed using the explicit code LS-DYNA. The results of the performed study show that introduction of viscous fillers indeed increases the energy absorption capability of open-cellular material structures. Additionally, it was determined that the size of the cellular material (number of cells) dramatically influences the cellular structure response and that the filler influence is stronger in cellular structures with higher relative density. Ključne besede: cellular materials, computer simulation, deformation, mechanical properties Objavljeno: 31.05.2012; Ogledov: 635; Prenosov: 2 Polno besedilo (0,00 KB) |
4. Mathematical analysis of measured displacements with emphasis on polynomial interpolationBoštjan Kovačič, Rok Kamnik, Zdravko Kapović, 2009, izvirni znanstveni članek Opis: At the Faculty of Civil Engineering, the University of Maribor, in the Centre for Geodesy, we have been primarily dealing with the study of displacements and application of results on deformations and mathematical analyses for the last 10 years. According to these results, we wanted to find a connection between displacements and resulting deformations in mathematical terms. For this purpose, experimental load-bearing test of a concrete girder was carried out step by step up to crack. Additionally, concrete girder was analytically modelled and also photogrammetric, geodetic, and physical methods were compared. During the process of analyzing the results, further polynomial interpolation was performed through which the displacements in the intermediate stages were calculated. Polynomial interpolation can also help in accomplishment of load-bearing experiments of larger structures. Ključne besede: geodesy, vertical movement, deformation, mathematical analysis Objavljeno: 31.05.2012; Ogledov: 724; Prenosov: 2 Polno besedilo (0,00 KB) |
5. Microcrack initiation and growth in heat-risistant 15Kh2MFA steel under cyclic loadingP. Yasniy, V.B. Hlado, V. Hutsaylyuk, Tomaž Vuherer, 2005, izvirni znanstveni članek Opis: This paper presents the results of investigation of a nuclear reactor pressurevessel steel 15Kh2MFA of two strength levels under cyclic loading. Themechanism of microcrack formation on the surface and in the bulk of 15Kh2MFA steel under cyclic deformation was investigated. Analysis of the specimen surfaces has shown that microcracks are caused by cyclic sliding in grains most favourably oriented with respect to the direction of the maximum shear stresses. Transmission electron microscope investigations show that microcracks in the material inside the grains are formed mainly along the band-type dislocation structure parallel to the dislocation subboundary. During cyclic deformation, the dislocation density on the subboundaries increases, in the local areas the dislocation density becomes limiting and it reaches the plasticity limit and causes microcrack formation. The interrelation of the average length of microcracks and their surface density with the energy density of inelastic deformation has been found. Ključne besede: material testing, nuclear reactor, pressure vessel, cyclic loading, cyclic deformation, dislocation structure, fatigue crack growth, TEM, fracture mechanics Objavljeno: 01.06.2012; Ogledov: 748; Prenosov: 5 Polno besedilo (0,00 KB) |
6. The analysis of permanent deformations of repeatedly loaded gravels from the Mura regionGregor Ficko, Bojan Žlender, 2005, izvirni znanstveni članek Opis: This contribution presents the results of the analysis of permanent deformations of gravel in the Mura region under repeated loading. The purpose of the analysis is to forecast the development of permanent normalised axial deformations ▫$/epsilon_1^{p*}$▫ regarding the number of loading cycles N and appurtenant stress states during cycling loading. The analysis used the results of tests performed by ZAG Ljubljana and Faculty of Civil Engineering and Geodesy (FGG) of the University of Ljubljana [1]. The analysis considers five types of stonematerials of different quantity of crushed grains in the mixture and of different water contents. Four types of stone materials are mixtures of different portions of crushed grains larger than 2 mm (Dcr = 87.7 %, 58.9 %, 32.6 % in 0 %), and of the water content around w = wopt - 2%. The stone material with portions of crushed grains larger than 2 mm Dcr= 58.9 % is analysed also for water content w = wopt + 0.7 %. The results of the analysis are deformations expressed as a function of the number of loading cycles N, and a spherical component of the repeated loading p and a distortional component of the repeated loading q. The results can be presentedas deformation surfaces in the ▫$/epsilon_1^{p*}$▫ - p - q space for an arbitrary number of cycles N. The relation between the spherical stress component p and the distortional stress component q, at arbitrary values of axial permanent deformations ▫$/epsilon_1^{p*}$▫, gives a failure envelope, and the so called deformation envelopes in the p - q space. The failure envelopes and deformation envelopes are given separately for five types of stone material. The deformation envelopes are low at small values of the axial permanent deformation ▫$/epsilon_1^{p*}$▫ When permanent axial deformations grow, the permanent deformation approaches the failure envelopes. The failure envelopes for individual types of stone material agree with research results performed by [1]. The analysis of permanent deformations also shows their dependence on the portion of crushed material Dcr in the mixture of crushed and uncrushed stone material. The deformation envelope for uncrushed stone material is situated in the lowest position, regarding the portion of crushed material in the mixture. With an increased portion of crushed material in the mixture of crushed and uncrushed stone material, the deformation envelope is also higher, similarly to the lawfulness of failure envelopes. The relation of failure and deformation envelopes is mathematically established as a function of the portion of crushed grains larger than 2 mm. The comparison of stone material results for different water contents shows that a minimal increase of water content above the optimal one essentially increases deformation. Ključne besede: building materials, Mura river gravel, cyclic triaxial tests, granular base material, permanent deformation, normalized axial permanent deformation Objavljeno: 01.06.2012; Ogledov: 695; Prenosov: 10 Polno besedilo (0,00 KB) |
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8. Computer-aided analysis of the forging processMatjaž Šraml, Janez Stupan, Iztok Potrč, Janez Kramberger, 2004, izvirni znanstveni članek Opis: This paper presents computer simulation of the forging process using the finite volume method (FVM). The process of forging is highly non-linear, where both large deformations and continuously changing boundary conditions occur. In most practical cases, the initial billet shape is relatively simple, but the final shape of the end product is often geometrically complex, to the extent that it is commonly obtained using multiple forming stages. Examples of the numerical simulation of the forged pieces provided were created using Msc/SuperForge computer code. The main results of the analysis are deformed shape, temperature, pressure, effective plastic strain, effective stress and forces acting on the die. Ključne besede: forging, computer simulation, finite volume method, deformation, stresses, material flow, industrial applications Objavljeno: 01.06.2012; Ogledov: 660; Prenosov: 6 Polno besedilo (0,00 KB) |
9. Coupled nonlineary problems in finite element analysis - a case studyIvana Atanasovska, Meri Burzić, Tomaž Vuherer, Dejan Momčilović, 2012, objavljeni znanstveni prispevek na konferenci Opis: The paper describes the Finite Element Method (FEM) analysis of elastic plastic deformation of steel tube impact absorbers for railway vehicles. Experiment investigation is used as a basis for FEM modelling and simulation. The developed FEM model includes material nonlinearity (plasticity), nonlinear contact and large deformation of finite elements. All aspects used in the absorber FEM model are explained in detail. The finite element analysis results for a chosen absorber are presented and discussed. The developed model opens the possibilities for future investigations of similar problems. Ključne besede: kinetic energy absorber, railway, elastic plastic deformation, contact, finite element analysis Objavljeno: 10.07.2015; Ogledov: 250; Prenosov: 2 Polno besedilo (0,00 KB) |
10. Determination of calibration function for fatigue crack propagation by measurment[!] surface deformationBruno Glaser, Aleksandar Veg, Patrik Gubeljak, Nenad Gubeljak, Jožef Predan, 2013, izvirni znanstveni članek Opis: Components and structures exposed to elastic dynamic loading respond with elastic strains on the surface of the material. Mechanical response could be monitored by deformations on the surface. The measurements and monitoring of these parameters could be performed with electronic devices for on-line measurements, controlled by computerized systems. In the case of fatigue crack initiation and propagation the cyclic strain amplitude deviated from initial strain response (mean value and amplitude). Implementation of appropriate monitoring system supported by computerized programs for evaluation, analyses and activation represent important means to safe service component or construction. To evaluate flaw depth growth, the strain gauge measuring sensors could be used. These sensors measure surface deformation relaxation due to flaw depth growth. The monitoring of the material under cyclic loading could be performed with experimentally determined calibration curve, representing deformation on the surface and depth of the semi-elliptical crack growth on the surface or cross section of the material. The goal of this paper is describe electronic device and experimental procedure in order to determine calibration function. Ključne besede: deformacije, elastičnost, rast razpoke, fatigue crack growth, surface deformation meaurement Objavljeno: 10.07.2015; Ogledov: 333; Prenosov: 1 Polno besedilo (0,00 KB) |