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Influence of Heat Treatments on Microstructure of Electron Beam Additive Manufactured Ti-6Al-4V Alloy
Damir Skuhala, 2020, magistrsko delo

Opis: Additive manufacturing of metallic parts is increasing in popularity and starting to emerge as a new competitive manufacturing process. Printed structures from Ti-6Al-4V titanium alloy, produced by electron beam additive manufacturing (EBAM), possess columnar prior β grains and layer bands, alongside an ultrafine lamellar microstructure, which is prone to low ductility and thus requiring thermal post-processing. Several heat treatments were performed in α + β and β field, in one or multiple stages. The results showed that bi-lamellar microstructure can be obtained, and that selection of annealing temperature and cooling rate determines the morphology, thickness, and distribution of both primary and secondary α features. Mechanical properties were evaluated on three selected heat treatments. Annealing of the As-built condition was performed at 710°C (HT1) and 870°C (HT2), resulting in lamellar microstructure with basketweave morphology. In two-stage heat treatment (HT3), the temperature in the first stage has exceeded β transus, while in the second, annealing was performed again at 870°C. The microstructure was characterized as a mixture of lamellar and bi-lamellar with large α colonies inside the rearranged prior β grains. Air cooling was performed in all HT from the final annealing stage. Strength and hardness have decreased with increasingly coarser microstructural features, while fracture toughness was improved, except in HT1, where the decrease in the fracture toughness was mainly attributed to reduced intrinsic toughening. As-built and HT1 conditions were effected by microstructural texture, causing inconsistent fracture morphology, reduced crack roughness and scattering in results. The influence of texture was decreased by coarser microstructure in HT2, while crack tortuosity was increased. Very unpredictable fracture behaviour was observed in HT3 due to large α colonies, as their orientation determines the areas of ductile or cleavage crack propagation.
Ključne besede: Titanium alloys, Ti-6Al-4V, additive manufacturing, EBAM, heat treatments, microstructural optimization, mechanical properties, fracture toughness
Objavljeno: 11.05.2020; Ogledov: 497; Prenosov: 140
.pdf Celotno besedilo (25,14 MB)

1st International FibreNet Science for the Public Day
2019, zbornik

Opis: First international conference in the scope of FibreNet project funded by European Commission. The conference brings the FibreNet together international representatives from industry and academia to discuss opportunities and strengths related to bio-based fibre products. In three consecutive sessions, fifteen international PhD students will present their research results, guide you along the value-chain of fibre-based products and give you the opportunity to discuss the future of bio-based materials.
Ključne besede: biobased materials, mechanical properties, paper, packaging, dissemination of research result
Objavljeno: 08.01.2020; Ogledov: 430; Prenosov: 25
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Engineering properties of tropical clay and bentonite modified with sawdust
Isaac I. Akinwumi, Oluwapelumi O. Ojuri, Adebanji S. Ogbiye, Colin A. Booth, 2017, izvirni znanstveni članek

Opis: Construction engineers typically avoid the use of expansive soils as construction materials because they are usually difficult to work on and can cause structural failure. This research work investigates how the application of sawdust to tropical clay and bentonite influences their geotechnical properties in order to determine their suitability for use as landfill-liner materials for the effective containment of toxic substances from landfills. X-ray diffractometry, X-ray fluorescence spectroscopy and scanning electron microscopy were used to determine the mineralogical composition, oxide composition and microstructure, respectively, of the clay and the bentonite. A series of laboratory tests were conducted to determine the specific gravity, Atterberg limits, compaction, unconfined compressive strength and permeability characteristics of the clay and the bentonite for varying proportions of sawdust application. Generally, increasing the percentage of sawdust caused a reduction in its specific gravity, maximum dry unit weight and unconfined compressive strength, while it caused an increase in the optimum moisture content and permeability of the modified clay and bentonite. The clay and bentonite both have a sufficiently low permeability that satisfies the hydraulic conductivity requirement for use as clay liners. Eight percent sawdust application to a clay having similar properties as that in this study is recommended as an economic way of modifying it – with the potential of improving its adsorbent property – for use in landfill-liner systems in order to prevent the toxic substances leaching from the landfills, thereby protecting the environment and public health.
Ključne besede: geotechnical properties, hydraulic barrier, landfill, construction, soil improvement, sustainability
Objavljeno: 18.06.2018; Ogledov: 391; Prenosov: 30
.pdf Celotno besedilo (766,16 KB)
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Empirical correlation between the shear-wave velocity and the dynamic probing heavy test
Stjepan Strelec, Davor Stanko, Mario Gazdek, 2016, izvirni znanstveni članek

Opis: Varaždin is located in the north-western part of Croatia in shallow quaternary alluvial sediments of the Drava River basin. Local site effects due to the alluvial soft sediments can play a crucial role in the amplification of seismic-wave ground motions. The shear-wave velocity (VS) is one of the most important parameters for determining dynamic soil properties and ground-response analyses. The seismic surface wave method (MASW) is the simplest and a very efficient way of measuring the shear-wave velocity in the field. The Dynamic Probing Heavy (DPH) test is suited to determining the soil strength and the soil deformation properties. However, there are a lack of correlations between the shear-wave velocity and the DPH tests (VS - NDPH) in the literature. In this paper we present empirical correlations between the shear-wave velocity VS and the soil penetration resistance NDPH with: a) raw (original) NDPH data: VS = 97.839·NDPH0.395, (R2 = 0.723); b) a groundwater correction NDPH data: VS = 92.998·NDPH0.363 (R2 = 0.815). From the measured DPH data, the shear-wave velocity (VS), the shear modulus (Go) and the Young’s modulus (Eo and Er) were estimated. Two different approaches (low vs. high strain) were compared, and the results were found to be in good agreement when the relative difference between the velocities is small and smooth. Dynamic probing tests are good for studying a discrete point of interest in a large field area based on preliminary seismic tests. The suggested correlation VS - NDPH can be used for a rough estimation of VS from NDPH (they are site-specific, and so not applicable worldwide). In this way valuable information about dynamic soil properties can be extracted for ground-response analyses and the study of local site effects.
Ključne besede: shear-wave velocity, MASW, DPH, empirical correlations, dynamic elastic moduli, dynamic soil properties
Objavljeno: 15.06.2018; Ogledov: 781; Prenosov: 38
.pdf Celotno besedilo (1,34 MB)
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Numerical simulation of intact rock behaviour via the continuum and Voronoi tesselletion models
Teja Fabjan, Diego Mas Ivars, Vladimir Vukadin, 2015, izvirni znanstveni članek

Opis: The numerical simulation of intact rock microstructure and its influence on macro-scale behaviour has received a lot of attention in the research community in recent years. Generating a grain-like structure with polygonal area contacts is one of the avenues explored for describing the rock’s microstructure. A Voronoi tessellation implemented in the Universal Distinct-Element Code (UDEC) is used to generate models with a polygonal microstructure that represent intact rock. The mechanical behaviour of the Voronoi polygons is defined by micro-properties, which cannot be measured directly in the laboratory. A numerical calibration procedure is needed to produce the macroscopic response of a model that corresponds to the material behaviour measured during a laboratory experiment. In this research, Brazilian, direct tensile, uniaxial compressive and biaxial test models are constructed to simulate the intact rock behaviour under a standard laboratory stress. An extensive series of parametric sensitivity analyses are executed in order to understand the influence of the input micro-properties on every model test behaviour and predict the relation between the micro-properties and the model’s macro response. The results can be treated as general guidelines for a complete and efficient intact rock calibration procedure. In parallel, a continuum-based model using the Mohr-Coulomb constitutive relationship is running as a benchmark. It has been shown that the Voronoi-based models through their microstructure approach better reproduce the Brazilian to direct tensile strength ratio, and show a better representation of the dilation, crack pattern and post-peak behaviour in comparison to continuum models.
Ključne besede: distinct-element method, parametric sensitivity analysis, intact rock, Voronoi tessellation, micromechanical properties, standard laboratory test
Objavljeno: 15.06.2018; Ogledov: 700; Prenosov: 63
.pdf Celotno besedilo (1,57 MB)
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Effects of ground granulated blast-furnace slag on the index and compaction parameters of clayey soils
Osman Sivrikaya, Selman Yavascan, Emre Cecen, 2014, izvirni znanstveni članek

Opis: The use of industrial wastes in soil stabilization not only provides for the re-use of waste materials, which may cause environmental pollution, but also leads to cost benefits. In this context, the use of industrial wastes in the stabilization of fine-grained soils has become a research topic in recent years. The aim of this study is to evaluate the potential use of granulated blast-furnace slag (GBFS) in clayey soil stabilization. In this study, the GBFS obtained from the Iskenderun iron-steel plant as an industrial waste was ground into two different fineness levels, and the effects of their incorporation into low-plasticity Kolsuz clay and high-plasticity bentonite clay in various rates (5%, 10%, 20%, 30%, and 50%) on the particle weight of unit volume, the consistency limits, and the compaction parameters are investigated. Based on the experimental results, it is clear that the GBFS has a positive effect on the stabilization of both clayey soils. It was also concluded that the improvement in bentonite clay is greater than that in Kolsuz clay. Thus, GBFS seems to be a promising material for the stabilization of clayey soils.
Ključne besede: clayey soils, index properties, granulated blast-furnace slag, stabilization
Objavljeno: 14.06.2018; Ogledov: 325; Prenosov: 102
.pdf Celotno besedilo (134,83 KB)
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Book of abstracts
2018, druge monografije in druga zaključena dela

Ključne besede: mechanical engineering, metalurgy, material properties
Objavljeno: 22.05.2018; Ogledov: 461; Prenosov: 0

The influence of porosity on geomechanical characteristics of snail soil in the Ljubljana Marsh
Bojan Žlender, Ludvik Trauner, 2006, izvirni znanstveni članek

Opis: This article focusses on mineralogical and physical characteristics of snail soil and their influence on parameter values of geomechanical characteristics.Snail soil, which got its name from fossil remains, is a typical layer observed in the Ljubljana marsh. It is distincltly porous, saturated and in a liquid consistency state. Snail soil was investigated for mineralogical and physical characteristics in the Laboratory of Soil Mechanics, Faculty of Civil Engineering of the University in Maribor. Mineral and chemical composition, visual appearance, specific surface and grain property were determined. Physical characyteristics show that snail soil is saturated in nature, highly porous and almost liquid. Geomechanical characteristics were investigated for their interdependency on physical characteristics. A series of triaxial tests were performed on snail soil samples of different porosity, density and water content. Cylindrical samples of the height of 100 mm and the diameter of 50 mm were tested using three-axial testing apparatus. The results of the tests show that interdependency exists between geomechanical characteristics and porosity. These relationships can be expressed as functions of density, porosity or water content. It is evident from the results that changes of the coefficient of permeability, the coefficient of consolidation, and the coefficient of volume compressibility are nonlinear with respect to changes in porosity. Changes of mechanical parameters, such as Young`s modulus, Poisson`s ratio andfriction angle are indistinct and almost linear at lower changes of porosity.
Ključne besede: geomechanics, properties of soils, snail soil, triaxial testing, porosity, permeability, consolidation, Young`s modulus, Poisson`s ratio, shear angle
Objavljeno: 17.05.2018; Ogledov: 658; Prenosov: 40
.pdf Celotno besedilo (486,06 KB)
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Ground-sourced energy wells for heating and cooling of buildings
Heinz Brandl, Dietmar Adam, Roman Markiewicz, 2006, izvirni znanstveni članek

Opis: Energy wells are thermo-active elements for an economical extraction or storage of ground energy, similar to energy piles and other deep foundation elements also used as heat exchangers. Heating and/or cooling of buildings requires a primary and secondary thermo-active circuit, commonly connected by a heat pump. The paper gives several design aspects of energy wells which can be also used for the design of deep energy foundations. Thermal response tests have proved suitable for the in-situ determination of thermal ground properties required for an optimised design. Moreover, different systems of energy wells are discussed, and a comprehensive pilot research project is described.
Ključne besede: energy wells, energy foundations, geothermal geotechnics, geothermal heating/cooling, thermo-active structures, thermal ground properties, field testing
Objavljeno: 17.05.2018; Ogledov: 374; Prenosov: 84
.pdf Celotno besedilo (4,24 MB)
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