Faculty of Mechanical Engineering

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Author: search.filters.author.Elisaveta DonchevaLanguage: search.filters.language.English

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    Sustainability and environmental life cycle analysis of welding processes
    (International Journal of Structural Integrity, Emerald Publishing Limited, 2024-07-29)
    Elisaveta Doncheva
    ;
    Nikola Avramov
    ;
    Aleksandra Krstevska
    ;
    Martin Petreski
    ;
    Jelena Djokikj
    Purpose–Welding is a widely used manufacturing process in many industries. The process consumes a lot of energy and resources, pollutes the environment, and emits gases and fumes into the atmosphere that are dangerous to human health. There are various welding processes, and the suitable welding process is usually chosen based on cost, material, and conditions. Subjectivity is the most significant impediment to selecting an optimal process. As a result, it is critical to develop the appropriate set of criteria, use the best tool and methodology, and collect sufficient data. This study examines the sustainability of welding processes and their environmental impact. Design/methodology/approach– The welding process’s sustainability was examined and discussed in general, considering the technological specifics of each welding process, physical performance, and environmental, economic, and social effects. The study investigates the environmental impact of MMAW, GMAW, and GTAW/GMAW processes through experimental work and LCA methodology. Findings– MMAW is the most environmentally harmful technology, whereas GMAW has the least impact. The GTAW/GMAW process outperformed the other processes in terms of yield stress, but the analyses revealed that it had a greater environmental impact than GMAW. Originality/value– The study provides an environmental impact summary and demonstrates the effects of welding parameters and processes. This gives users an understanding of choosing the best welding technique or making the process more environmentally friendly. These recommendations help policymakers identify hot spots and implement the right plans to achieve more sustainable manufacturing.
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    A REVIEW STUDY ON HYDROGEN EMBRITTLEMENT OF STEEL
    (Society for structural integrity and life “Prof. Dr Stojan Sedmak” Institute for materials testing (IMS), Belgrade, 2024-11-23)
    Elena Anastasovska
    ;
    Elisaveta Doncheva
    ;
    Filip Zdraveski
    A common and intricate phenomenon known as hydrogen embrittlement of steel is the deterioration of the mechanical properties of metal in relation to stress corrosion cracking. This phenomenon has been extensively studied, with numer ous works proposed over the last two decades, but there is still a lack of unified solutions and a solid understanding of the phenomenon. The purpose of this paper is to provide a review of the literature and publications on hydrogen embrittlement in steel. It focuses on recent developments and methods that have contributed to a better understand ing of the relationship between steel structure, properties, and performance, with a particular emphasis on hydrogen diffusion, characterisation, mechanisms, and prevention of hydrogen embrittlement in structural steel. Furthermore, the paper discusses recent advances in experimental and multi-scale modelling and proposes future studies to address challenges related to hydrogen embrittlement in steels.
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    Wire-arc additive manufacturing: recent developments and potential
    (The Academy of Applied Technical Studies Belgrade, 2023-12)
    Elisaveta Doncheva
    ;
    Aleksandra Krstevska
    ;
    Marjan Djidrov
    ;
    Filip Zdraveski
    ;
    Trajche Velkovski
    Wire-arc additive manufacturing (WAAM) is a promising technology for producing medium and large components without traditional subtracting technologies. It is a hybrid of two manufacturing techniques: additive manufacturing and welding. The use of this technology has grown significantly due to advantages such as material and energy savings while achieving high deposition rates and low cost. However, there are some issues with microstructure homogeneity, and properties are affected due to the complexity of the arc-induced thermal cycles and metallurgical mechanisms, resulting in high residual stresses, distortion, porosity, cracks, and delamination. This article summarises the progress made in the field of wire additive manufacturing, with a focus on welding systems, tool path design software, material analysis, and control systems. It also highlights some critical aspects that must be addressed to ensure high-quality production, such as control and diagnosis mechanisms for defect monitoring, the effects of parameters and their optimisation possibilities for improving quality, ensuring process stability, and possible post-deposition heat treatments. The conclusions suggest further improvements to the wire-additive manufacturing process in terms of accuracy, reliability, and efficacy, as well as future applications of the technology and research activities.
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    Numerical investigation of micro-structural influence on stress distribution in heat affected zone of a welded joint
    (SCIENTIFIC ASSOCIATION FOR DEVELOPMENT AND AFFIRMATION OF NEW TECHNOLOGIES, 2015-12)
    Elisaveta Doncheva
    The preliminary motivation for this paper is numerical investigation of stress distribution in heat affected zones of welded joints. The micro-structural complexity of the characteristic zones increase the difficulty in investigating the relationship between micro-structural morphologies and mechanical properties. In order to investigate this relationship, several 2D numerical models are constructed with randomly obtained grain boundaries and grains with different shapes, sizes and components. The Voronoi tessellation is used to represent the microstructures and the finite element calculation is conducted on the ABAQUS computing platform after the finite element simulation model is built up. The construction of representative volume elements (RVE), material characterization, meshing techniques and boundary conditions used in numerical models are described in detail. The interpretation of the results obtained from the numerical models are graphically displayed and analyzed. Results show that stress value and distribution within different zones is related to grains orientation and the orientation of its neighboring grains. Furthermore, the numerical investigations show that definition of material characteristics on grain level is extremely important in order to simulate accurate results. The differences between mechanical properties obtained in models with fine-grained and coarse-grained microstructure lead to conclusions that grain boundaries greatly affect stress and deformation distributions.