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Gdańsk University of Technology

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Publications from the year 2024

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  • Corrosion Monitoring in Petroleum Installations—Practical Analysis of the Methods
    • Juliusz Orlikowski
    • Agata Jazdzewska
    • Iwona Łuksa
    • Michał Szociński
    • Kazimierz Darowicki
    2024 Full text Materials

    This paper presents the most typical corrosion mechanisms occurring in the petroleum industry. The methods of corrosion monitoring are described for particular corrosion mechanisms. The field and scope of the application of given corrosion-monitoring methods are provided in detail. The main advantages and disadvantages of particular methods are highlighted. Measurement difficulties and obstacles are identified and widely discussed based on actual results. Presented information will allow the corrosion personnel in refineries to extract more reliable data from corrosion-monitoring systems.

  • Corrosion of AISI1018 and AISI304 steel exposed to sulfates
    • Ginneth Millan Ramirez
    • Miguel Angel Baltazar-Zamora
    • Ce Tochtli Méndez Ramírez
    • Maciej Niedostatkiewicz
    • Hubert Byliński
    2024 Inżynieria Bezpieczeństwa Obiektów Antropogenicznych

    This research analyses the behavior of corrosion, durability, and quality of reinforced concrete samples coated with two different materials when exposed to contaminated soil with sulfates. The initial assessment involved evaluating the water absorption rate of the coating materials before and after exposure to a solution containing 3%푁푎2푆푂4+3%푀푔푆푂4+3%퐾2푆푂4+3%퐶푎푆푂4to determine their durability. the corrosion potential and linear polarization resistance technique were employed to measure the corrosion rate. Carbon steel and AISI 304 steel bars were tested alongside a stainless counter electrode. The findings indicate that the solvent-based coating exhibited superior performance, demonstrating reduced corrosion and water absorption rates. Additionally, the presence of sulfates led to the formation of a surface layer on the concrete, initially aiding in limiting waterpenetration. However, over time, this layer eventually causes damage to the concrete from the inside out.

  • Corrosion performance of super duplex stainless steel and pipeline steel dissimilar welded joints: a comprehensive investigation for marine structures
    • Anup Kumar Maurya
    • Shailesh M. Pandey
    • Rahul Chhibber
    • Dariusz Fydrych
    • Chandan Pandey
    2024 INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY

    This study investigates the corrosion behavior of dissimilar gas tungsten arc (GTA) welded joints between super duplex stainless steel (sDSS 2507) and pipeline steel (X-70) using electrochemical and immersion corrosion tests. The GTA welds were fabricated using ER2594 and ER309L fller metals. The study examined the electrochemical characteristics and continuous corrosion behavior of samples extracted from various zones of the weldments in a 3.5 wt.% NaCl solution, employing electrochemical impedance spectroscopy, potentiodynamic polarization methods, and an immersion corrosion test. EIS and immersion investigations revealed pitting corrosion in the X-70 base metal/X-70 heat-afected zone, indicating inferior overall corrosion resistance due to galvanic coupling. The corrosion byproducts identifed in complete immersion comprised α-FeOOH, γ-FeOOH, Fe3O4, and Fe2O3, whereas γ-FeOOH and Fe3O4 were predominant in dry/wet cyclic conditions. Corrosion escalated with dry/wet cycle conditions while maintaining a lower level in complete immersion. The corrosion mechanism involves three wet surface stages in dry/wet cycles and typical oxygen absorption during complete immersion. Proposed corrosion models highlight the infuence of Cl−, O2, and rust layers.

  • Cost-effective methods of fabricating thin rare-earth element layers on SOC interconnects based on low-chromium ferritic stainless steel and exposed to air, humidified air or humidified hydrogen atmospheres
    • Łukasz Mazur
    • Paweł Winiarski
    • Bartosz Kamecki
    • Justyna Ignaczak
    • Sebastian Molin
    • Tomasz Brylewski
    2024 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY

    Most oxidation studies involving interconnects are conducted in air under isothermal conditions, but during real-life solid oxide cell (SOC) operation, cells are also exposed a mixture of hydrogen and water vapor. For this study, an Fe–16Cr low-chromium ferritic stainless steel was coated with different reactive element oxides – Gd2O3, CeO2, Ce0.9Y0.1O2 – using an array of methods: dip coating, electrodeposition and spray pyrolysis. The samples underwent oxidation experiments carried out over 100 h in three different atmospheres at 800 °C: air, an air/H2O mixture, and an Ar/H2/H2O mixture. The influence of different atmospheres on the corrosion of the Fe–16Cr steel was determined via oxidation kinetics studies; the corrosion product was evaluated using X-ray diffraction, scanning electron microscopy and area-specific resistance (ASR) measurements. All coated samples exhibited lower parabolic oxidation rate constants than bare steel and most also had lower ASR. The applied modifications were found to be sufficiently effective to allow the investigated low-chromium steel to be considered for application as an interconnect material for SOCs.

  • Cost-Effective Piggyback Forward dc-dc Converter
    • Oleksandr Matiushkin
    • Oleksandr Husev
    • Hossein Afshari
    • Dmitri Vinnikov
    • Ryszard Strzelecki
    2024

    The novel piggyback dc-dc converter as a cost-effective solution is presented in this work. It provides a wide input voltage range of regulation with a low component count. The novel solution is an advanced forward dc-dc converter with an additional clamp output capacitor. The idea of such a type of converter is to transfer magnetizing energy of transformer to the output side, instead of using input clamp circuit. The design guidelines of the passive component of the proposed solution are discussed. A digital domain proportional integral controller is designed for the off-grid system validation, and it provides a stable output voltage in a wide range of the input voltage and power. Experimental prototype of the proposed piggyback converter along with experimental results of critical points are presented. The efficiency study of the proposed solution is done.

  • Cost-Efficient Globalized Parameter Optimization of Microwave Components through Response-Feature Surrogates and Nature-Inspired Metaheuristics
    • Anna Pietrenko-Dąbrowska
    • Sławomir Kozieł
    • Łukasz Gołuński
    2024 Full text IEEE Access

    Design of contemporary microwave devices predominantly utilizes computational models, including both circuit simulators, and full-wave electromagnetic (EM) evaluation. The latter constitutes the sole generic way of rendering accurate assessment of the system outputs that considers phenomena such as cross-coupling or radiation and dielectric losses. Consequently, for reliability reasons, the final tuning of microwave device parameters is commonly performed utilizing EM simulation software. As EM analysis is computationally heavy, parametric optimization entails significant costs, also for local algorithms. The expenses generated by global search procedures are incomparably higher, and often prohibitive. Still, global optimization is more and more often necessary, for example, when re-designing a structure over extended ranges of operating conditions (bandwidth, power split ratios, etc.), when more than a single local optimum exists (e.g., optimization of frequency selective surfaces), or simply due to the absence of quality initial design (e.g., compact circuits obtained using the slow-wave phenomenon). A possible workaround is surrogate-assisted optimization, yet a construction of accurate replacement models is a challenge by itself. This paper offers an innovative approach to a rapid globalized optimization of passive microwave components. It combines a machine learning procedure, specifically, an iterative construction and refinement of fast surrogates (with infill criterion being a minimization of the predictor-yielded objective improvement) with a response feature technology, where the metamodel targets suitably appointed characteristic points of the circuit outputs. These so-called response features are in a nearly linear relationship with the geometry parameters, which facilitates the search process and reduces the expenditures associated with surrogate model construction. Identification of the infill points is executed using a particle swarm optimization algorithm. Numerical experiments carried out using two microstrip circuits demonstrate the capability for a global search of the proposed algorithm, and its superior performance over direct nature-inspired-based optimization and surrogate-assisted search at the level of complete circuit characteristics.

  • Cost-Efficient Measurement Platform and Machine-Learning-Based Sensor Calibration for Precise NO2 Pollution Monitoring
    • Anna Pietrenko-Dąbrowska
    • Sławomir Kozieł
    • Marek Wójcikowski
    • Bogdan Pankiewicz
    • Artur Rydosz
    • Tuan-Vu Cao
    • Krystian Wojtkiewicz
    2024 MEASUREMENT

    Air quality significantly impacts human health, the environment, and the economy. Precise real-time monitoring of air pollution is crucial for managing associated risks and developing appropriate short- and long-term measures. Nitrogen dioxide (NO2) stands as a common pollutant, with elevated levels posing risks to the human respiratory tract, exacerbating respiratory infections and asthma, and potentially leading to chronic lung diseases. Notwithstanding, precise NO2 detection typically demands complex and costly equipment. This paper explores NO2 monitoring using low-cost platforms, meticulously calibrated for reliability. An integrated measurement unit is first presented that contains primary and supplementary nitrogen dioxide sensors, as well as auxiliary detectors for evaluating outside and inside temperature and humidity. The calibration process utilizes data acquired over the period of five months from various reference stations. Employing machine learning with an artificial neural network (ANN)-based and kriging interpolation surrogate models, the correction strategy integrates additive and multiplicative enhancement, predicted by the ANN through auxiliary sensor data such as temperature, humidity, and the sensor-detected NO2 levels. Extensive verification studies showcase that this calibration approach notably enhances monitoring precision (r2 correlation coefficient surpassing 0.85 concerning reference data, and RMSE of less than four g/m3), rendering low-cost NO2 detection practical and dependable.

  • Cost-Efficient Multi-Objective Design of Miniaturized Microwave Circuits Using Machine Learning and Artificial Neural Network
    • Sławomir Kozieł
    • Anna Pietrenko-Dąbrowska
    • Leifur Leifsson
    2024

    Designing microwave components involves managing multiple objectives such as center frequencies, impedance matching, and size reduction for miniaturized structures. Traditional multi-objective optimization (MO) approaches heavily rely on computationally expensive population-based methods, especially when exe-cuted with full-wave electromagnetic (EM) analysis to guarantee reliability. This paper introduces a novel and cost-effective MO technique for microwave passive components utilizing a machine learning (ML) framework with artificial neural network (ANN) surrogates as the primary prediction tool. In this approach, mul-tiple candidate solutions are extracted from the Pareto set via optimization using a multi-objective evolutionary algorithm (MOEA) applied to the current ANN model. These solutions expand the dataset of available (EM-simulated) parameter vectors and refine the surrogate model iteratively. To enhance computational effi-ciency, we employ variable-resolution EM models. Tested on two microstrip cir-cuits, our methodology competes effectively against several surrogate-based ap-proaches. The average computational cost of the algorithm is below three hundred EM analyses of the circuit, with the quality of generated Pareto sets surpassing those produced by the benchmark methods.

  • Coupled DEM/CFD analysis of impact of free water on the static and dynamic response of concrete in tension regime
    • Marek Krzaczek
    • Andrzej Tejchman-Konarzewski
    • Michał Nitka
    2024 Full text COMPUTERS AND GEOTECHNICS

    W tym artykule zbadano numerycznie quasi-statyczne i dynamiczne zachowanie częściowo nasyconego płynem betonu w warunkach dwuwymiarowego (2D) jednoosiowego rozciągania w mezoskali. Obliczono, jaki wpływ ma zawartość wolnego płynu porowego (gazu i wody) na proces pękania i wytrzymałość betonu w rozciąganiu. Do symulacji zachowania betonu całkowicie i częściowo nasyconego płynem w warunkach quasi-statycznych i dynamicznych wykorzystano ulepszony model hydromechaniczny w skali porów, oparty na DEM/CFD. Podstawą koncepcji przepływu płynu była sieć kanałów na ciągłym obszarze pomiędzy dyskretnymi elementami. W bardzo porowatym, częściowo nasyconym betonie przyjęto dwufazowy laminarny przepływ płynu. Aby śledzić zawartość cieczy/gazu, wzięto pod uwagę położenie i objętość porów i rys. Symulacje numeryczne spójnych próbek ziarnistych o uproszczonej mezostrukturze sferycznej przypominającej beton przeprowadzono w warunkach suchych i mokrych dla dwóch różnych szybkości odkształcenia. Przeprowadzono badania wpływu ciśnienia porów płynu, nasycenia płynu i lepkości płynu na wytrzymałość i proces pękania betonu. Kwasi-statyczna wytrzymałość na rozciąganie spadała nieliniowo wraz ze wzrostem nasycenia płynu i lepkości płynu podczas migracji płynu przez pory i pęknięcia wskutek przyspieszenia procesu pękania. Jednakże podczas szybkiego dynamicznego odkształcenia przy rozciąganiu proces pękania został osłabiony z powodu ograniczenia migracji płynu wynikającego z niewystarczającego czasu płynu na opuszczenie porów. Spowodowało to nieliniowy wzrost dynamicznej wytrzymałości na rozciąganie wraz ze wzrostem nasycenia płynu i lepkości płynu.

  • Coupling between the photoactivity and CO2 adsorption on rapidly thermal hydrogenated vs. conventionally annealed copper oxides deposited on TiO2 nanotubes
    • Wiktoria Lipińska
    • Katarzyna Grochowska
    • Jacek Ryl
    • Jakub Karczewski
    • Mirosław Sawczak
    • Emerson Coy
    • Vincent Mauritz
    • Ryan Crisp
    • Katarzyna Siuzdak
    2024 JOURNAL OF MATERIALS SCIENCE

    Highly ordered spaced titanium dioxide nanotubes were fabricated via electrochemical anodization and modified with titania nanoparticles and copper oxides. Such materials were rapidly annealed in hydrogen atmosphere or conventionally in a tube furnace in air, in which the temperature slowly increases. Applied synthesis procedure can be considered as simple, cost-effective, and environmentally friendly as it allows for reduction in used materials and enhances sustainable engineering. Manipulating the chemical composition of materials by different thermal treatments resulted in various photoelectrochemical activities and density of CO2 adsorption sites. Rapidly annealed nanotubes decorated by copper oxides exhibit excellent electrochemical properties where one electrode combines both: solar to electricity conversion (photocurrent under visible light 30 µA/cm2) and CO2 adsorption systems (18 times higher current after CO2 saturation). Rapidly thermal hydrogenated TiO2 nanotubes with copper oxides had 17 times higher photocurrent and wider absorption band (380–780 nm) than conventionally annealed ones. Furthermore, the crystal planes such as Cu (111), Cu (220), Cu2O (110), CuO (002) and Cu0, Cu+, Cu2+ oxidation states, and oxygen vacancies were recognized for hydrogenated sample. It should be highlighted that thermal annealing conditions significantly affects ability of copper oxide to CO2 adsorption and CO2 reduction reaction for hydrogenated electrode.

  • Crack monitoring in concrete beams under bending using ultrasonic waves and coda wave interferometry: the effect of excitation frequency on coda
    • Magdalena Knak
    • Erwin Wojtczak
    • Magdalena Rucka
    2024 Full text

    Concrete is one of the most widely used construction materials in the world. In recent years, various non-destructive testing (NDT) and structural health monitoring (SHM) techniques have been investigated to improve the safety and control of the current condition of concrete structures. This study focuses on micro-crack monitoring in concrete beams. The experimental analysis was carried out on concrete elements subjected to three-point bending in a testing machine under monotonic quasi-static loading. During the tests, the fracture process was characterized using ultrasonic waves. The recorded signals were further processed by coda wave interferometry (CWI). This technique allowed the detection of cracks using the decorrelation between ultrasonic wave signals collected at different stages of degradation. Different values of excitation frequencies in the range from 100 kHz to 400 kHz were used to investigate the influence of frequency selection on the effectiveness of the damage indication based on the decorrelation of coda waves. The results obtained from the experiments were intended to highlight the effect of the applied frequencies on the coda wave interferometry.

  • Crank–Nicolson FDTD Method in Media Described by Time-Fractional Constitutive Relations
    • Damian Trofimowicz
    • Tomasz Stefański
    • Jacek Gulgowski
    2024

    In this contribution, we present the Crank-Nicolson finite-difference time-domain (CN-FDTD) method, implemented for simulations of wave propagation in media described by time-fractional (TF) constitutive relations. That is, the considered constitutive relations involve fractional-order (FO) derivatives based on the Grünwald-Letnikov definition, allowing for description of hereditary properties and memory effects of media and processes. Therefore, the TF constitutive relations make it possible to include, in a dielectric response, diffusion processes which are modelled mathematically by the diffusion-wave equation. We formulate fundamental equations of the proposed CN-FDTD method, and then we execute simulations which confirm its accuracy and applicability. Additionally, we perform numerical tests of stability, which confirm unconditional stability of the method. The proposed method is useful for researchers investigating numerical techniques in media described by FO derivatives.

  • Creating private and public value in data-related management projects: a cross-border case study from Switzerland and Italy
    • Elide Garbani-Nerini
    • Elena Marchiori
    • Nadzeya Sabatini
    • Lorenzo Cantoni
    2024 Full text

    The literature in the field of smart cities shows a continuous emphasis and interest in the topic of big data due to the extensive use of Information and Communication Technologies by public and private institutions within each city. There is undoubtedly value in big data: in data lie insights on the city, its stakeholders, citizens, products, and services. Challenges, though, lie in data’s variety, volume, and velocity, but also in managing them, considering the complex interplay between stakeholders inside a city or a country. Another layer of complexity is added when we consider a smart city as a smart destination where the visitor - often an international tourist - becomes an additional stakeholder of a smart city bringing in additional data. Such challenges, though, are even stronger when tourists do not stop at geographical borders: smart destinations become cross-border destinations. While there is a physical border between them, but most importantly, a legal difference in how data should be collected, stored, managed, and re-used [56, 59], data flows do not stop at this border. This complexity has to be managed both by governmental and tourism agencies. However, the literature between eGovernment and tourism is often theoretical in nature, and while it highlights the potential benefits of smart destinations and data-management processes, it does not provide detailed guidelines on how to implement these concepts in practice [41], especially in the context of cross-border smart destinations. With regards to this, not only has the need for guidelines risen to help tourism destinations tackle smart data- and technology-related projects, but also to define how stakeholders can come together to determine data policies and governance in order to create private as well as public value [60]. This paper responds to such a need by presenting the results of a cross-border research project conducted in Switzerland and Italy, where the model of a smart destination’s structure proposed by Ivars-Baidal et al. [35] has been applied, and its dimensions have been operationalized in a data-related management project. This allowed the authors to understand how to create public and private value managing data flows in a cross-border context, while also elaborating on the model reflecting on data’s dual role as a starting point but also as a central component impacting other dimensions.

  • Creep rupture study of dissimilar welded joints of P92 and 304L steels
    • Gaurav Dak
    • Krishna Guguloth
    • R. S. Vidyarthy
    • Dariusz Fydrych
    • Chandan Pandey
    2024 Welding in the World

    The present work investigates the high-temperature tensile and creep properties of the dissimilar metal weld joints of 304L austenitic stainless steel (SS) and P92 creep strength-enhanced ferritic-martensitic (CSEF/M) steel under diferent testing condition. Thermanit MTS 616 fller rod (P92 fller) and the multi-pass tungsten inert gas (TIG) welding process were used to create the dissimilar weld connection. The ultimate tensile strength (UTS) was evaluated in the temperature range of 450–850 °C. Creep testing was conducted at a temperature of 650 °C while applying stress levels of 130 MPa, 150 MPa, 180 MPa, and 200 MPa. The shortest creep life (2.53 h) was recorded for the specimen tested at 650 °C and subjected to 200 MPa, whereas the longest creep life (~242 h) was observed for the specimen tested at 650 °C with a stress of 130 MPa. The linear regression model was developed using an applied stress (σ) v/s rupture time (tR) plot at 650 °C. The applied stress and rupture time followed the logarithmic equation: log(tR)=22.57566+(-9.55294) log (σ). The detailed microstructural characterization and micro-hardness distribution across the fractured specimens was carried out. The fndings demonstrated that the service life span of this weld joint at high temperature and stress conditions is infuenced by the undesired microstructural changes at elevated temperature, such as coarsening of the precipitates, development of the Laves phase, softening of the matrix, and strain-ageing phenomenon.

  • Cryptocurrencies as a Speculative Asset: How Much Uncertainty is Included in Cryptocurrency Price?
    • Tayyaba Ahsan
    • Krystian Zawadzki
    • Khan Mubashir
    2024 Full text SAGE Open

    The aim of this paper is to examine the relationship between uncertainty indices (Geopolitical Uncertainty Index and Global Economic Policy Uncertainty Index) and cryptocurrencies. This study evaluated the behavior of cryptocurrencies with the evolution of uncertainties (GPU, EPU) on returns and volatility in terms of safe heaven as in traditional specualtive assets it increases their volaitility and reduces risk. For this purpose, this study examines the relationship between uncertanities indices, gold returns and crptocurrency by using the OLS regression for the monthly data from April 2017 to April 2022. The findings of this study indicate that the return and volatility of cryptocurrency increases. In particular, we note that the cryptocurrency market could serve as a weak hedge and safe against GEPU during a bull market; It could be considered a strong hedge, but in most cases could not serve as a safety against GPR. However, in case of Gold it is found that it serves as weak hedge against uncertainity indices and is not considered as safe heaven against GEPU and GPR. This study expands the current research on uncertainity indices and provides unique insight about the speculative nature of cryptocurrencies and safe heaven.

  • CuMn1.7Fe0.3O4 – RE2O3 (RE=Y, Gd) bilayers as protective interconnect coatings for Solid Oxide Cells
    • Bartłomiej Lemieszek
    • Justyna Ignaczak
    • Krystian Lankauf
    • Patryk Błaszczak
    • Maciej Bik
    • Marcin Zajac
    • Maciej Sitarz
    • Piotr Jasiński
    • Sebastian Molin
    2024 Full text JOURNAL OF THE EUROPEAN CERAMIC SOCIETY

    Efficient replacement of materials based on critical elements such as cobalt is one of the greatest challenges facing the field of solid oxide cells. New generation materials, free of cobalt show potential to replace conventional materials. However, these materials are characterized by poor ability to block chromium diffusion. This article described the study of CuMn1.7Fe0.3O4 (CMFO) spinel combined with single metal oxide (Y2O3 or Gd2O3) thin films as protective coatings for steel interconnects. CMFO was examined using XRD and TPR. Coated steel samples were oxidized in an air atmosphere at 700 °C for 4000 h. The coatings and oxide scale microstructures and cross-sections were examined by CRI, XRD, and SEM-EDX. The electrical properties of the steel-coating system were evaluated using Area Specific Resistance measurements. Based on the results obtained, it can be concluded that the use of thin layers of rare earth oxides allowed for better blocking of chromium diffusion.

  • Current advances in membrane processing of wines: A comprehensive review
    • Youssef El Rayess
    • Roberto Castro Munoz
    • Alfredo Cassano
    2024 Full text TRENDS IN FOOD SCIENCE & TECHNOLOGY

    Background Membrane-based operations, especially pressure-driven membrane operations, are today well-established procedures for various applications in the wine industry thanks to their intrinsic properties and undoubted advantages over traditional methods. Emerging membrane processes, such as pervaporation, electrodialysis and osmotic distillation, forward osmosis, membrane contactors, offer new and interesting perspectives to improve quality and develop new products without compromising organoleptic properties. Scope and approach This review provides a comprehensive overview on the use of membrane operations in wine processing. A bibliometric and scientometric analysis has been done to provide the current advances dealing with the application of these operations in different steps of wine manufacture, including clarification, stabilization, concentration, acidification, deacidification and dealcoholization. The current challenges and perspectives are highlighted to guide further advancements of membrane technology in this field. Key findings and conclusions The use of conventional and emerging membrane systems offers interesting opportunities to improve and optimize current practices of the wine processing industry. Considerable progress has been done concerning the development of low-fouling materials, identification of wine molecules responsible for membrane fouling and methods to mitigate such phenomenon in the clarification of wines by microfiltration membranes. Technological progress in electrodialysis makes this process a very attractive method for tartrate stabilization, acidification and deacidification of wines. Different conventional and emerging membrane processes offer valid post-fermentation strategies to remove ethanol in wines while preserving their original characteristics. The global results provide interesting perspectives for a wider implementation of membrane processes in the winemaking industry and to redesign the traditional vinification process under the process intensification strategy.

  • Cybersecurity Assessment Methods—Why Aren’t They Used?
    • Rafał Leszczyna
    2024 IT Professional

    A recent survey of cybersecurity assessment methods proposed in academic and research environments revealed that their adoption in operational settings was extremely scarce. At the same time, the frameworks developed by industrial communities have been met with broad reception. The question arises of what contributed to the success of the methods. To answer it, three-part research that employed evaluation criteria, qualitative metrics, and continuity of support assessment was conducted. Among other findings, it shows that the continuity of support plays an important role in the adoption of a method. This, in turn, is connected to a sound funding model and a well-developed and active community of supporters.

  • Cyclic behaviour modelling of additively manufactured Ti-6Al-4V lattice structures
    • Michał Doroszko
    • Andrzej Seweryn
    2024 INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES

    The present work is concerned with the numerical modelling of the cyclic behaviour of Ti-6Al-4V lattice structures. In the study, diamond structures of titanium alloy produced by the additive laser powder bed fusion (LPBF) method with different degrees of relative density were used. Realistic geometric models of the studied mesostructures were generated using computed microtomography, taking into account the imperfections of the material resulting from the manufacturing process. The numerical calculations also took into account the actual material hardening curve in the elastic-plastic strain range. One of the achievements of this work is the numerical modelling of cyclic loading of realistic mesostructures with their imperfections. The areas of the mesostructures most susceptible to fatigue cracking have been identified and analysed. True hysteresis loops and values of local stress and strain amplitude were determined at the locations of highest stress concentration in cyclically loaded diamond structures. The main achievement of the present work was the modelling of the macroscopic fatigue life of the investigated mesostructures based on the true values of stress and strain at the locations most exposed to fatigue cracking. For this purpose, a stress criterion for fatigue cracking of Ti-6Al-4V lattice structures fabricated by the additive LPBF method was proposed.

  • Cyclic deformation and fracture behaviour of additive manufactured maraging steel under variable-amplitude loading
    • Zbigniew Marciniak
    • Ricardo Branco
    • Wojciech Macek
    • Michał Dobrzyński
    • C. Malça
    2024 THEORETICAL AND APPLIED FRACTURE MECHANICS

    The cyclic deformation and fracture behaviour of 18Ni300 maraging steel produced by laser beam powder bed fusion is studied under variable-amplitude loading. The tests were conducted under fully-reversed strain-controlled conditions with a loading sequence comprising three ascending cycles and three descending cycles repeated sequentially until failure. After the tests, fracture surfaces were examined using height and volume surface topography parameters to characterise the fractographic features. Fracture surfaces were also analysed through scanning electron microscopy to identify the main failure modes. Fatigue life was predicted by using the Smith-Watson-Topper and the Basquin-Coffin-Manson models with the Palmgren-Miner damage rule. The former approach was more accurate leading to mean errors close to zero. The values of the kurtosis parameter obtained from both sides of the fracture surfaces correlated well with the fatigue life. SEM analysis showed a mixed ductile-brittle mode of fracture with a predominance of brittle fracture. Crack initiation occurred from manufacturing defects located at the surface or near-surface.