1. Simulation and mechanical properties of fine-grained heat-affected zone microstructure in 18CrNiMo7-6 steelTomaž Vuherer, Fidan Smaili, Edvard Bjelajac, Mirza Manjgo, Gorazd Lojen, 2022, izvirni znanstveni članek Opis: Heat-affected zones (HAZs) in real welds are usually quite narrow, and consequently most standard mechanical tests are difficult or even impossible. Therefore, simulated microstructures are often used for mechanical tests. However, the most often used weld thermal cycle simulator produces only a few millimeters wide area of simulated microstructure in the middle of specimens. Consequently, these kind of simulated specimen are not suitable for standard tensile tests, and even for Charpy impact tests, the simulated area can be too narrow. Therefore, to investigate the mechanical properties of a fine-grain heat-affected zone in 18CrNiMo7-6 steel, two methods were used for simulation of as-welded microstructures: (a) a weld thermal cycle simulator, and (b) as an alternative, though not yet verified option, austenitizing in a laboratory furnace + water quenching. The microstructures were compared and mechanical properties investigated. The grain sizes of the simulated specimens were 10.9 μm (water-quenched) and 12.6 μm (simulator), whereby the deviations from the real weld were less than 10%. Both types of simulated specimen were used for hardness measurement, Charpy impact tests, and fatigue tests. Water-quenched specimens were large enough to enable standard tensile testing. A hardness of 425 HV, yield strength Rp02 = 1121 MPa, tensile strength Rm = 1475 MPa, impact energy KV = 73.11 J, and crack propagation threshold ΔKthR = 4.33 MPa m0.5 were obtained with the water quenched specimens, and 419 HV, KV = 101.49 J, and ΔKthR = 3.4 MPa m0.5 with the specimens prepared with the simulator. Comparison of the results confirmed that the annealed and quenched specimens were suitable for mechanical tests of FG HAZs, even for standard tensile tests. Due to the use of simulated test specimens, the mechanical properties determined can be linked to the FG HAZ microstructure in 18CrNiMo7-6 steel. Ključne besede: weld joint, fine-grained HAZ, simulation of microstructure, hardness, impact toughness, tensile properties, fatigue crack growth, 18CrNiMo7-6 steel Objavljeno v DKUM: 05.12.2024; Ogledov: 0; Prenosov: 1 Celotno besedilo (5,22 MB) Gradivo ima več datotek! Več... |
2. Behaviour of cellular metamaterials under impact loading conditions : doctoral disertationYunus Emre Yilmaz, 2024, doktorska disertacija Opis: This doctoral thesis investigates cell-size-graded metallic and non-metallic Triply Periodic
Minimal Surface (TPMS) structures' behavior under varying loading rates. Using experimental
tests, analytical calculations, and advanced computer simulations, the research explores the
interplay between material properties, cell size grading, and deformation mechanisms under
different strain rates. The study focuses on enhancing the Direct Impact Hopkinson Bar (DIHB)
setup for accurate force and displacement measurements and pioneering a method for
quantifying inertial forces, critical at high strain rates.
Key findings show that cell-size grading significantly affects deformation patterns, with initial
deformation occurring in regions with smaller and lower stiffness cells across different loading
rates and TPMS geometries. The research also highlights topology's influence on mechanical
response, with photopolymer-based diamond structures showing superior energy absorption
and gas-atomized steel structures favoring gyroid configurations. This underscores the
importance of considering both topology and base material selection during TPMS design. The
study demonstrates the increasing prominence of inertial forces as deformation rates rise,
impacting structural response and failure likelihood in TPMS structures.
These insights inform the design of optimized cellular metamaterials for high-performance
applications requiring superior energy absorption and structural integrity under high loading
rates. The research advances material characterization techniques and computational
modelling capabilities, contributing to the development of next-generation cellular
metamaterials for broader engineering applications. Ključne besede: Triply Periodic Minimal Surfaces, TPMS, Cell-size-grading, Impact, High-strainrate, Digital Image Correlation Objavljeno v DKUM: 17.10.2024; Ogledov: 0; Prenosov: 16 Celotno besedilo (46,48 MB) |
3. Supply chain perspectives for achieving economic growth and environmental sustainabilityRebeka Kovačič Lukman, Kristijan Brglez, Maja Fošner, 2024, drugi znanstveni članki Opis: A resilient supply chain is crucial for economic growth and the well-being of economies. However, it contributes to environmental challenges, such as resource extraction, material usage, climate change and biodiversity. This Special Volume of the Journal of Logistics, Supply Chain, Sustainability, and Global Challenges explores current research directions and challenges while offering solutions for sustainable supply chains. The volume examines existing European policy directives and strategies to comprehensively understand sustainable supply chain requirements. It conducts a content analysis of the current research in the field. The authors present valuable theoretical insights and empirical case studies addressing the interplay between sustainable supply chains, economic growth, and environmental impact mitigation. The papers in this Special Volume highlight the holistic and interconnected nature of the supply chain field and emphasise that there is still significant potential for improving supply chain processes to enhance their sustainability. Ključne besede: sustainable supply chains, economic growth, environmental impact, industry 4.0 Objavljeno v DKUM: 01.10.2024; Ogledov: 0; Prenosov: 5 Povezava na datoteko Gradivo ima več datotek! Več... |
4. Toward an economy of wellbeing : the economic impact of the Welsh healthcare sectorTimotej Jagrič, Christine Elisabeth Brown, Dušan Fister, Oliver Darlington, Kathryn Ashton, Mariana Dyakova, Mark Bellis, Vita Jagrič, 2022, izvirni znanstveni članek Opis: Population health and wellbeing is both a result, as well as a driver, of economic development and prosperity on global, European, national and sub-national (local) levels. Wales, one of the four United Kingdom (UK) nations, has shown a long-term commitment to sustainable development and achieving prosperity for all, providing a good example of both national and sub-national level, which can be useful for other European countries and regions. In this paper, the economic importance of the healthcare sector to the Welsh economy is explored. We use a large number of data sources for the UK and Welsh economy to derive an economic model for 2017. We estimate output, income, employment, value-added, and import multipliers of the healthcare sector. Results suggest that the healthcare sector has an above average contribution in four explored economic aspects of the Welsh economy (output, income, employment, value-added), according to its impact on the surrounding economic ecosystem. Also, it is below average regarding leaking through imports. The multipliers' values offer empirical evidence when deciding on alternative policy actions. Such actions can be used as a stimulus for encouraging regional development and post-COVID economic recovery. Our study refers to the Welsh healthcare sector's economic impact as a whole. Therefore, we suggest investigating the economic impact of individual healthcare providers in the future. Ključne besede: input-output analysis, healthcare sector, Wales, impact analysis, economy of wellbeing Objavljeno v DKUM: 17.06.2024; Ogledov: 181; Prenosov: 17 Celotno besedilo (544,71 KB) Gradivo ima več datotek! Več... |
5. Comparison of the mechanical properties of hardfacings made by standard coated stick electrodes and a newly developed rectangular stick electrodeEdvard Bjelajac, Andrej Skumavc, Gorazd Lojen, Mirza Manjgo, Tomaž Vuherer, 2024, izvirni znanstveni članek Opis: Cladding with a stick electrode is one of the oldest arc processes for adding a deposit on a base material. The process is suitable for outdoor working, but the disadvantages are low productivity and large dilution rates. In this work, a simple solution is proposed, which would enable cladding of a larger area with one pass and decrease the dilution rate at the same time—a new type of electrode was developed, exhibiting a rectangular cross-section instead of a round one. Hardfacings, welded with E Fe8 electrodes according to EN 14 700 Standard were welded on mild steel S355 J2 base material with three different coated stick electrodes. The first one was a commercially available, standard, round hardfacing electrode, the second was the same, but with a thinner coating, and the third one was a newly developed rectangular electrode. All three types had equal cross-sections of the metallic core and the same type of coating. Manufacturing of the rectangular electrodes in the laboratory is explained briefly. One- and multi-layer deposits were welded with all three types. Differences were observed in the arc behavior between the round and rectangular electrodes. With the rectangular electrode, the microstructure of the deposit was finer, penetration was shallower, and dilution rates were lower, while the hardness was higher, residual stresses predominantly compressive, and the results of instrumented Charpy impact tests and fracture mechanics tests were better. Ključne besede: hardfacing, dilution rate, hardness, Charpy impact toughness, residual stress, fracture toughness Objavljeno v DKUM: 14.05.2024; Ogledov: 298; Prenosov: 16 Celotno besedilo (10,82 MB) Gradivo ima več datotek! Več... |
6. Hydrogen production, storage and transport for renewable energy and chemicals : An environmental footprint assessmentRobert Hren, Annamaria Vujanović, Yee Van Fan, Damjan Krajnc, Jiri Klemeš, Lidija Čuček, 2023, izvirni znanstveni članek Ključne besede: hydrogen producing technologies, hydrogen storage, hydrogen transport, life cycle assessment, different electricity sources, energy and environmental footprints, eco-benefit and eco-cost, comparative impact assessment Objavljeno v DKUM: 10.05.2024; Ogledov: 240; Prenosov: 34 Celotno besedilo (2,48 MB) Gradivo ima več datotek! Več... |
7. Experimental study of crack propagation through cladded 316L/S355 steel produced by the hot-roll bonding processEdvard Bjelajac, Andrej Skumavc, Fidan Smaili, Gorazd Lojen, Jožef Predan, Tomaž Vuherer, 2023, izvirni znanstveni članek Opis: A hot-rolled clad plate made of 316L stainless steel and S355 carbon steel was produced in a real industrial environment via GMAW welding, vacuuming, preheating to 1240 °C, and hot-roll bonding on four stand plate mills in nine passes with reduction rates between 20-6% per pass. The clad plates were solution annealed to achieve the usual delivery condition. Ultrasound testing showed a bonding rate of 100%. Metallographic examination revealed predominantly low concentrations of oxides at the interface. The tensile strength of the bond reached 155 MPa. The shear strength always satisfied the requirements of ASTM A264. It was observed that the concentration of oxide particles influenced the shear strength strongly. The lowest measured value was 172 MPa. Specimens notched in the base material and specimens notched in the clad layer were used in the Charpy impact test. In every case, only the notched layer broke, while the other layer was only bent. The absorbed energies were always higher than those of each material alone. Fracture mechanic tests gave similar results. The crack could not propagate from the notched layer into the other one, regardless of the material of the notched layer. Instead, delamination occurred. Due to delamination, K1c could not be determined, so KQ was given instead. Ključne besede: clad plate, hot-roll bonding, shear strength, tensile strength, impact toughness, crack propagation Objavljeno v DKUM: 28.03.2024; Ogledov: 210; Prenosov: 17 Celotno besedilo (18,79 MB) Gradivo ima več datotek! Več... |
8. Evaluation of the impact and fracture toughness of a nanostructured bainitic steel with low retained austenite contentMihael Brunčko, Peter Kirbiš, Ivan Anžel, Leo Gusel, Darja Feizpour, Tomaž Irgolič, Tomaž Vuherer, 2023, izvirni znanstveni članek Opis: The impact and fracture toughness of a nanostructured, kinetically activated bainitic steel was determined using Standard methods. Prior to testing, the steel was quenched in oil and aged naturally for a period of 10 days in order to obtain a fully bainitic microstructure with a retained austenite content below 1%, resulting in a high hardness of 62HRC. The high hardness originated from the very fine microstructure of bainitic ferrite plates formed at low temperatures. It was determined that the impact toughness of the steel in the fully aged condition improved remarkably, whereas the fracture toughness was in line with expectations based on the extrapolated data available in the literature. This suggests that a very fine microstructure is most beneficial to rapid loading conditions, whereas material flaws such as coarse nitrides and non-metallic inclusions are the major limitation for obtaining a high fracture toughness. Ključne besede: evaluation of fracture toughness, impact toughness, nanostructured bainite, natural aging, low retained austenite content, kinetically activated bainite KAB Objavljeno v DKUM: 16.02.2024; Ogledov: 390; Prenosov: 29 Povezava na celotno besedilo Gradivo ima več datotek! Več... |
9. Dynamic characterisation of novel three-dimensional axisymmetric chiral auxetic structureAnja Mauko, Yunus Emre Yilmaz, Nejc Novak, Tomáš Doktor, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek Opis: The study presents an extensive mechanical and computational characterisation of novel cellular metamaterial with axisymmetric chiral structure (ACS) at different strain rates. The Direct Impact Hopkinson Bar (DIHB) testing device was used for impact testing up to 21 m/s striker speed, which was insufficient to reach the shock deformation regime. Thus, using computational simulations to estimate the structure behaviour at high strain rates was necessary. Experimental and computational results showed that all ACS structures exhibit a nominal stress–strain relationship typical for cellular materials. As the loading conditions shifted to a dynamic regime, the micro–inertia effect became increasingly pronounced, leading to a corresponding rise in structure stiffness. The Poisson's ratio in all ACS increases gradually, making them superior to traditional cellular materials, which experience a sudden increase in Poisson's ratio during loading. Additionally, the study found that the structures exhibited a rise in the auxetic effect with an increase in strain rate, highlighting the benefits of axisymmetric structures in high-loading regimes. Overall, the obtained results provide valuable insights into the mechanical properties of ACS under different loading regimes and will contribute to further design improvements and the fabrication of novel ACS metamaterials. Ključne besede: axisymmetric chiral structure, auxetic, chiral unit cell, impact testing, dynamic characterisation, finite element simulations Objavljeno v DKUM: 15.02.2024; Ogledov: 345; Prenosov: 29 Celotno besedilo (7,73 MB) Gradivo ima več datotek! Več... |
10. High-Order Fiber Bragg Grating Corrosion Sensor Based on the Detection of a Local Surface ExpansionVedran Budinski, Matej Njegovec, Simon Pevec, Boris Macuh, Denis Đonlagić, 2023, izvirni znanstveni članek Opis: This paper presents a fiber optic sensor for the detection of corrosion processes that occur on metal surfaces. In the proposed sensor design, a sensing fiber with an inscribed high-order Bragg grating is attached to the observed metal surface. A broadening of high-order Bragg grating spectral characteristics is observed and used to detect small and highly localized longitudinal strain variations that occur along the fiber as a result of corrosive rust flakes' formations beneath the sensing fiber. The proposed approach provides a straightforward fabrication method, the possibility for unobtrusive mounting, including mounting of the sensor beneath the corrosion-protective layers, and consistent corrosion detection yields. Ključne besede: optical fiber sensors, corrosion, impact of corrosion, optic sensors Objavljeno v DKUM: 09.02.2024; Ogledov: 320; Prenosov: 21 Celotno besedilo (1,58 MB) Gradivo ima več datotek! Več... |