1. A rapid thermal-radiation-assisted sintering strategy for Nd-Fe-B-type magnetsTomaž Tomše, Aljaž Iveković, Andraž Kocjan, Sašo Šturm, Kristina Žužek Rožman, 2024, izvirni znanstveni članek Povzetek: The green transition has spiked demand for high-performance sintered Nd-Fe-B permanent magnets, necessitating advanced powder consolidation technologies to enhance production efficiency. This study explores the rapid sintering methodology for an Nd-Fe-B powder using a radiation-assisted sintering approach. The case study material is an industrially used powder, prepared through strip-casting, hydrogen decrepitation, and jet milling, with a mean particle size of 5.5 µm. The powder is sintered to full density in a modified Spark Plasma Sintering furnace, achieving pressureless conditions and eliminating electrical currents in the sample to preserve grain alignment and prevent decomposition of the hard-magnetic phase. Fully-dense samples are obtained with heating rates ranging from 10 to 200 °C/min and up to 5 minutes of dwell time at 1100 °C. Rapid heating results in grain size and microstructure comparable to conventionally sintered magnets prepared from the same powder, without compromising magnetic performance after post-sinter annealing at 520 °C for 120 minutes. This sintering method contributes to a novel strategy for optimizing magnet production by utilizing efficient thermal-radiation heat transfer. The combination of rapid heating and pressureless sintering drastically reduces heat-up and dwell times, providing a fundamental advantage over slow conventional sintering.
Ključne besede: rapid sintering, finite-element modeling
Objavljeno v DiRROS: 28.03.2025; Ogledov: 150; Prenosov: 50
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2. The impact of a thermal insulation layer on the seismic performance of energy-efficient buildingsStanislav Lenart, Siva Ram Karumanchi, 2024, objavljeni znanstveni prispevek na konferenci Povzetek: Energy-efficient homes are constructed with a continuous and uniform thermal envelope and are commonly built on top of a thermal insulation (TI) layer that encloses the entire building. Lightweight aggregates such as foamed glass aggregate, expanded clay aggregate, and extruded polystyrene (XPS) insulation boards are commonly used as materials for the TI layer to prevent thermal bridging at the ground floor slab. However, the reinforced concrete slab foundation above the TI layer is susceptible to horizontal sliding during seismic loading. To improve the seismic behavior of buildings founded on TI layers, this study discussed the shear stiffness and damping characteristics of lightweight aggregates and three types of XPS boards through laboratory tests available in the literature. A 2-dimensional numerical analysis is performed, and the corresponding validation results of the simulations are presented. The effect of TI layers on the seismic performance of buildings constructed with TI layers made from these materials is assessed. A comparative analysis of various interface conditions of the TI materials under seismic loading is also conducted. Overall, this research aims to enhance the resilience and sustainability of energy-efficient homes by investigating the impact of TI layers on their seismic performance. The findings provide valuable insights for designing more robust structures that can withstand seismic events.
Ključne besede: energy-efficient buildings, thermal insulation, extruded polystyrene (XPS), finite element analysis, foamed glass aggregate, seismic response
Objavljeno v DiRROS: 21.01.2025; Ogledov: 174; Prenosov: 89
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3. Numerical evaluation of suction effects and groundwater table variations on long-term pavement subgrade performanceSiva Ram Karumanchi, Anirban Mandal, Stanislav Lenart, 2024, izvirni znanstveni članek Povzetek: Over the past few decades, flexible pavements across the globe have seen a significant reduction in their service life due to climate changes. The flexible pavements with unsaturated sub- grades undergo volumetric changes during the drying and wetting phases, affecting their long-term deformation behavior. These phases cause significant variations in matric suction and groundwater table depth. This study employs a coupled pore pressure-deformation analysis on flexible pavements to investigate the impact of groundwater table depth and suction variations in unsaturated subgrades. Finite-element simulations using the Abaqus and developed USDFLD code were validated against literature data. Sensitivity analysis was conducted by varying the suctions in subgrades during drying and subsequent wetting to evaluate the groundwater table depth. Furthermore, under heavy cyclic wheel loading, pavement-deformation analysis was conducted to investigate the influence of subgrade suction. The findings demonstrate that, after an initial drying phase at 5000 kPa suction, wetting over 180 days caused the groundwater level to rise from 5.45 m beneath the subgrade to the surface. This led to a 98% increase in surface-vertical deformations due to cyclic wheel loading after 180 days of wetting compared to the deformations during the drying phase at the same suction level. This assessment of groundwater-depth variations and long-term deformation behavior with the impact of suction improves the design and sustainability of flexible pavements.
Ključne besede: flexible pavement, unsaturated soil, suction, finite-element method
Objavljeno v DiRROS: 21.01.2025; Ogledov: 162; Prenosov: 107
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5. Lessons learned from the monitoring of retaining structures, built in demanding geotechnical conditions in SloveniaPavel Žvanut, Janko Logar, 2019, objavljeni znanstveni prispevek na konferenci Povzetek: A typical retaining structure built with large-diameter bored piles in soft clastic rock, and sup-ported by pre-stressed permanent ground anchors, is discussed. Step-by-step back analyses were performed. A simplified geological structure was first used in the analyses, together with a simple Mohr-Coulomb model. The results were compared with more complex analyses using a Hardening Soil model and a more detailed geological structure. Much better results were obtained with the use of the HS model, which is more suitable for the modelling of rock of such a type, but even with the use of the MC model the final results were quite good, making the use of the observational method attractive for engineers.
Ključne besede: geotechnics, gretaining structures, bored piles, numerical modelling, finite element method, observational method
Objavljeno v DiRROS: 27.03.2024; Ogledov: 599; Prenosov: 313
Celotno besedilo (1,67 MB)
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6. Numerical modeling in electroporation-based biomedical applicationsNataša Pavšelj, Damijan Miklavčič, 2008, izvirni znanstveni članek Povzetek: Background. Numerous experiments have to be performed before a biomedical application is put to practical use in clinical environment. As a complementary work to in vitro, in vivo and medical experiments, we can use analytical and numerical models to represent, as realistically as possible, real biological phenomena of, in our case, electroporation. In this way we canevaluate different electrical parameters in advance, such as pulse amplitude, duration, number of pulses, or different electrode geometries. Suchnumerical models can contribute significantly to the understanding of an experiment and treatment planning as well as to the design of new electroporation devices and electrodes. Methods. We used commercially available modeling software, based on finite element method. We constructed a model of a subcutaneous tumor during electrochemotherapy (EMAS) and a model ofskin during gene electrotransfer (COMSOL Multiphysics). Tissue-electrode geometries, pulse parameters and currentvoltage measurements from in vivo experiments were used to develop and validate the models. Results. To describeadequately our in vivo observations, a tissue conductivity increase during electroporation was included in our numerical models. The output currents of the models were compared to the currents and the voltages measuredduring in vivo experiments and a good agreement was obtained. Also, when comparing the voltages needed for a successful electropermeabilization assuggested by the models, to voltages applied in experiments and achieving a successful electrochemotherapy or in vivo gene electrotransfer, good agreementcan be observed. Conclusions. Modeling of electric current and electric field distribution during cell and tissue electroporation proves to be helpful in describing different aspects of the process and allowing us to design electrodes and electroporation protocols as a part of treatment planning.
Ključne besede: electroporation, gene electrotransfer, electrochemotherapy, subcutaneous tumor, finite-element method
Objavljeno v DiRROS: 07.03.2024; Ogledov: 694; Prenosov: 183
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7. 3D finite element analysis of a concrete dam behavior under changing hydrostatic load : a case studyPavel Žvanut, 2022, izvirni znanstveni članek Povzetek: In this study, a large arch-gravity Moste Dam was analyzed, where an automated system for the measurements of horizontal displacements of the upper part of the dam was established. Two-dimensional (2D) and three-dimensional (3D) analyses of dam behavior, taking into account the earth pressures and the hydrostatic load, using the finite element method (FEM)-based computer program DIANA, were performed. The influence of lowering the water level of the reservoir by 6.2 m, on the horizontal displacements of the upper part of the dam, at stationary temperature conditions, was investigated. It was found that the results of the performed 2D and 3D FEM analyses fitted in very well with the result of experimentally determined measurement of horizontal displacements (which was 0.48 mm in the upstream direction) that was obtained using a hanging pendulum. An additional comparison of the results of 3D calculations showed that the finite element mesh density had a small effect on the calculated horizontal displacements.
Ključne besede: concrete dam, finite element method, material properties, structure behavior, measuring instruments, monitoring, ime series analysis, horizontal displacements, hydrostatic pressure
Objavljeno v DiRROS: 21.06.2023; Ogledov: 955; Prenosov: 514
Celotno besedilo (5,35 MB)
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8. Model updating concept using bridge Weigh-in-Motion dataDoron Hekič, Andrej Anžlin, Maja Kreslin, Aleš Žnidarič, Peter Češarek, 2023, izvirni znanstveni članek Povzetek: Finite element (FE) model updating of bridges is based on the measured modal parameters and less frequently on the measured structural response under a known load. Until recently, the FE model updating did not consider strain measurements from sensors installed for weighing vehicles with bridge weigh-in-motion (B-WIM) systems. A 50-year-old multi-span concrete highway viaduct, renovated between 2017 and 2019, was equipped with continuous monitoring system with over 200 sensors, and a B-WIM system. In the most heavily instrumented span, the maximum measured longitudinal strains induced by the full-speed calibration vehicle passages were compared with the modelled strains. Based on the sensitivity study results, three variables that affected its overall stiffness were updated: Young’s modulus adjustment factor of all structural elements, and two anchorage reduction factors that considered the interaction between the superstructure and non-structural elements. The analysis confirmed the importance of the initial manual FE model updating to correctly reflect the non-structural elements during the automatic nonlinear optimisation. It also demonstrated a successful use of pseudo-static B-WIM loading data during the model updating process and the potential to extend the proposed approach to using random B-WIM-weighed vehicles for FE model updating and long-term monitoring of structural parameters and load-dependent phenomena.
Ključne besede: monitoring, bridge, viaduct, bridge weigh-in-motion (B-WIM), structural health monitoring (SHM), finite element (FE), calibration, model updating
Objavljeno v DiRROS: 29.05.2023; Ogledov: 1031; Prenosov: 471
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9. Impact of metakaolin on mechanical performance of flax textile-reinforced cement-based compositesFilip Majstorović, Václav Sebera, Maruša Mrak, Sabina Dolenec, Marco Wolf, Laetitia Sarah Jennifer Marrot, 2022, izvirni znanstveni članek Povzetek: This study presents research on the effect of Portland cement (PC) replacement with metakaolin on the mechanical behavior of flax textile-reinforced cementitious matrices (TRCM). The composition of cementitious matrices and in-situ flax fibres was determined using X-ray diffraction and thermogravimetric analysis, while the reinforcement efficiency of the textile and mechanical behavior of TRCMs was investigated by three-point bending tests and finite element analysis. High amounts of PC replacement with metakaolin provided a calcium hydroxide-free environment, more suitable for the natural fibres, to avoid their degradation and embrittlement and, thus, significantly contribute to the ductility of the cement-based composite material.
Ključne besede: textile-reinforced concrete (TRC), flax textile, natural fibres, finite element, metakaolin, cement-based composites, open access
Objavljeno v DiRROS: 22.05.2023; Ogledov: 943; Prenosov: 456
Celotno besedilo (8,40 MB)
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