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1.
Experimental characterization and phase-field damage modeling of ductile fracture in AISI 316l
Vladimir Dunić, Nenad Gubeljak, Miroslav Živković, Vladimir Milovanović, Darko Jagarinec, Nenad Djordjevic, 2024, original scientific article

Abstract: ) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements.
Keywords: phase-field damage modeling, ductile fracture, crack-tip opening displacement, crack growth, resistance curve, finite element method, simulations
Published in DKUM: 19.09.2024; Views: 0; Downloads: 8
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2.
Experimental and numerical analysis of fracture mechanics behavior of heterogeneous zones in S690QL1 grade high strength steel (HSS) welded joint
Damir Tomerlin, Dražan Kozak, Luka Ferlič, Nenad Gubeljak, 2023, original scientific article

Abstract: The heterogeneity of welded joints’ microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth.
Keywords: heterogeneous welded joint, high strength steel, mechanical testing, damage, fracture, mechanical properties, finite element analysis
Published in DKUM: 30.11.2023; Views: 405; Downloads: 27
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3.
Comparison and implementation of thermo-mechanical fatigue damage models : magistrsko delo
Jure Vinkovič, 2021, master's thesis

Abstract: The basis of the master thesis is an in-depth and comprehensive analysis of the scientific literature on damage models of thermo-mechanical fatigue. The aim of the thesis is to investigate and determine the suitability of damage models for their application in numerical simulations of components subjected to thermo-mechanical loading with in-phase, out-of-phase or constant temperature cycles. The theoretical background of material behavior under static and dynamic loads (e.g. low-cycle fatigue, high-cycle fatigue) is presented. The work also includes an overview of damage mechanisms typical of time-temperature varying loading conditions (e.g. cyclic softening and hardening of the material, mean stress relaxation, material creep, visco-plasticity, etc.). This is followed by a structured review of several damage models of thermo-mechanical fatigue (e.g. Neu-Sehitoglu, DTMF, Coffin-Manson, Ostergren, Smith-Watson-Topper, Unified Energy Approach, etc.). An overview of the experimental tests on aluminum alloy and cast iron carried out at temperatures up to 800 °C is given. The idea of processing the raw experimental data including the calibration procedure of the thermo-mechanical fatigue damage models is schematically illustrated and described. The basic mathematical laws of constitutive material models for both material types are given. In the conclusion of the MSc thesis, the correlations of the calibrated damage models are presented, which, together with the constructive opinions, give an important message on the application of the individual damage models depending on the type of material and the loading method.
Keywords: thermo-mechanical fatigue, constitutive material model, damage model, aluminum alloy, cast iron alloy, finite element method
Published in DKUM: 03.01.2022; Views: 1038; Downloads: 4
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4.
Patient's right to protection of personal data in the legal system of Bosnia and Herzegovina
Marko Bevanda, Maja Čolaković, 2017, original scientific article

Abstract: Health-related personal data belong to a category of sensitive data which, therefore, must be specially protected. The protection of personal health data is one of the patients´ fundamental rights. Doctors protect their patients´ interests only when the information gained about patients, while providing them medical treatment, are kept secret. In this paper, the authors provide an overview of the legal framework for the protection of health-related personal data in the legal system of Bosnia and Herzegovina. In addition to the analysis of the relevant legal provisions and considering the situation in practice, it can be concluded that formal harmonisation of legislation with the acquis communautaire in this field is not followed by effective implementation of regulation in practice.
Keywords: privacy, doctor, medical malpractice, liability for damage
Published in DKUM: 09.10.2018; Views: 1070; Downloads: 155
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5.
Damage and failure modeling of lotus-type porous material subjected to low-cycle fatigue
Janez Kramberger, Klemen Sterkuš, Srečko Glodež, 2016, original scientific article

Abstract: The investigation of low-cycle fatigue behaviour of lotus-type porous material is presented in this paper. Porous materials exhibit some unique features which are useful for a number of various applications. This paper evaluates a numerical approach for determining of damage initiation and evolution of lotus-type porous material with computational simulations, where the considered computational models have different pore topology patterns. The low-cycle fatigue analysis was performed by using a damage evolution law. The damage state was calculated and updated based on the inelastic hysteresis energy for stabilized cycle. Degradation of the elastic stiffness was modelled using scalar damage variable. In order to examine crack propagation path finite elements with severe damage were deleted and removed from the mesh during simulation. The direct cyclic analysis capability in Abaqus/Standard was used for low-cycle fatigue analysis to obtain the stabilized response of a model subjected to the periodic loading. The computational results show a qualitative understanding of pores topology influence on low-cycle fatigue under transversal loading conditions in relation to pore orientation.
Keywords: porous materials, low-cycle fatigue, damage, finite element analysis
Published in DKUM: 02.08.2017; Views: 1269; Downloads: 404
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6.
Computational simulation of biaxial fatigue behaviour of lotus-type porous material
Janez Kramberger, Marko Šori, Matjaž Šraml, Srečko Glodež, 2016, original scientific article

Abstract: A computational simulation of low-cycle fatigue behaviour of lotus-type porous material, subjected to biaxial in-phase loading cycles is presented in this paper. Fatigue properties of porous materials are less frequently published in the literature. This paper evaluates computational analyses, where different pore distribution and biaxial loading conditions in relation to the pore orientations is considered in each simulation. The fatigue analysis is performed by using a damage initiation and evolution law based on the inelastic strain energy. The computational results are subjected to the appropriate statistical analysis, because of different pore topology a different fatigue lives are obtained on the same loading level. Results of computational simulations show also a qualitative understanding of porosity influence on low-cycle fatigue failures of lotus-type porous material under biaxial loading conditions.
Keywords: Lotus-type porous material, low-cycle fatigue, damage, finite element analysis
Published in DKUM: 02.08.2017; Views: 1473; Downloads: 416
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7.
The SOS response master regulator LexA is associated with sporulation, motility and biofilm formation in Clostridium difficile
Beata Maria Walter, Stephen Cartman, Nigel Peter Minton, Matej Butala, Maja Rupnik, 2015, original scientific article

Abstract: The LexA regulated SOS network is a bacterial response to DNA damage of metabolic or environmental origin. In Clostridium difficile, a nosocomial pathogen causing a range of intestinal diseases, the in-silico deduced LexA network included the core SOS genes involved in the DNA repair and genes involved in various other biological functions that vary among different ribotypes. Here we describe the construction and characterization of a lexA ClosTron mutant in C. difficile R20291 strain. The mutation of lexA caused inhibition of cell division resulting in a filamentous phenotype. The lexA mutant also showed decreased sporulation, a reduction in swimming motility, greater sensitivity to metronidazole, and increased biofilm formation. Changes in the regulation of toxin A, but not toxin B, were observed in the lexA mutant in the presence of sub-inhibitory concentrations of levofloxacin. C. difficile LexA is, therefore, not only a regulator of DNA damage but also controls many biological functions associated with virulence.
Keywords: toxins, bacterial sporulation, DNA damage, antibiotics
Published in DKUM: 19.06.2017; Views: 1306; Downloads: 387
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8.
Low temperature impact toughness of the main gas pipeline steel after long-term degradation
P. O. Maruščak, Irina Danyliuk, R.T. Biščak, Tomaž Vuherer, 2014, original scientific article

Abstract: The correlation of microstructure, temperature and Charpy V-notch impact properties of a steel 17G1S pipeline steel was investigated in this study. Within the concept of physical mesomechanics, the dynamic failure of specimens is represented as a successive process of the loss of shear stability, which takes place at different structural/scale levels of the material. Characteristic stages are analyzed for various modes of failure, moreover, typical levels of loading and oscillation periods, etc. are determined. Relations between low temperature derived through this test, microstructures and Charpy (V-notch) toughness test results are also discussed in this paper.
Keywords: impact toughness, fracture, damage, gas pipeline, steel, degradation
Published in DKUM: 03.04.2017; Views: 1497; Downloads: 453
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9.
Automated diagnostics of damage to an aluminum alloy under the conditions of high-cycle fatigue
P. O. Maruščak, Igor Konovalenko, Mykhailo Karuskevich, Vladimir Gliha, Tomaž Vuherer, 2013, original scientific article

Abstract: An identification and quantitative analysis of the deformation relief of the aluminium alloy for an aircraft construction based on a digital-image processing has been performed. The behaviour of defects has been assessed on the basis of diagnostics results for individual stages of the deformation process. It has been established that the individual stages of the damage-accumulation process are characterised by the values of integral-image parameters. Based on the consecutive processing of the data on the surface cyclic deformation, the main regularities of the propagation of defects have been found. Theoretical preconditions have been substantiated and experimental results obtained.
Keywords: fatigue, surface, digital image, diagnostics, accumulated damage, defect propagation, evaluation
Published in DKUM: 10.07.2015; Views: 1503; Downloads: 111
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10.
In-service damage of railway steel axles
O. Jasnìî, Tomaž Vuherer, Ju. I. Pindus, Andriy Sorochak, Ivan Samardžić, 2011, other scientific articles

Abstract: The influence of temperature and specimens undercut place on impact toughness of railway axle material in service is investigated. The obtained results show inversely proportional dependence of impact toughness on undercut radius of specimens. The decrease of test temperature from +20 to –40 ºC decreases significantly the impact toughness and portion of ductile fracture.
Keywords: impact toughness, in-serice damage, railway axle, undercut
Published in DKUM: 01.06.2012; Views: 1388; Downloads: 98
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