1. Yield load solutions for SE(B) fracture toughness specimen with I-shaped heterogeneous weldPejo Konjatić, Marko Katinić, Dražan Kozak, Nenad Gubeljak, 2022, izvirni znanstveni članek Opis: The objective of this work was to investigate the fracture behavior of a heterogeneous
I-shaped welded joint in the context of yield load solutions. The weld was divided into two equal
parts, using the metal with the higher yield strength and the metal with the lower yield strength
compared to base metal. For both configurations of the I-shaped weld, one with a crack in strength
in the over-matched part of the weld and one for a crack in the under-matched part of the weld, a
systematic study of fracture toughness SE(B) specimen was carried out in which the crack length,
the width of the weld and the strength mismatch factor for both weld metals were varied, and the
yield loads were determined. As a result of the study, two mathematical models for determination
of yield loads are proposed. Both models were experimentally tested with one strength mismatch
configuration, and the results showed good agreement and sufficiently conservative results compared
to the experimental results.
Ključne besede: yield load, heterogeneous weld, numerical analysis, SE(B) specimen
Objavljeno v DKUM: 21.03.2025; Ogledov: 0; Prenosov: 0
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2. Effects of fixture configurations and weld strength mismatch on J-integral calculation procedure for SE(B) specimensPrimož Štefane, Stijn Hertelé, Sameera Naib, Wim de Waele, Nenad Gubeljak, 2022, izvirni znanstveni članek Opis: This work presents the development of a J-integral estimation procedure for deep and
shallow cracked bend specimens based upon plastic ηpl factors for a butt weld made in an S690 QL
high strength low alloyed steel. Experimental procedures include the characterization of average
material properties by tensile testing and evaluation of base and weld metal resistance to stable tearing
by fracture testing of square SE(B) specimens containing a weld centerline notch. J-integral has been
estimated from plastic work using a single specimen approach and the normalization data reduction
technique. A comprehensive parametric finite element study has been conducted to calibrate plastic
factor ηpl and geometry factor λ for various fixture and weld configurations, while a corresponding
plastic factor γpl was computed on the basis of the former two. The modified ηpl and γpl factors were
then incorporated in the J computation procedure given by the ASTM E1820 standard, for evaluation
of the plastic component of J and its corresponding correction due to crack growth, respectively. Two
kinds of J-R curves were computed on the basis of modified and standard ηpl and γpl factors, where
the latter are given by ASTM E1820. A comparison of produced J-R curves for the base material
revealed that variations in specimen fixtures can lead to ≈10% overestimation of computed fracture
toughness JIc. Furthermore, a comparison of J-R curves for overmatched single-material idealized
welds revealed that the application of standard ηpl and γpl factors can lead to the overestimation of
computed fracture toughness JIc by more than 10%. Similar observations are made for undermatched
single material idealized welds, where fracture toughness JIc is overestimated by ≈5%.
Ključne besede: metal weld, strength mismatch, fracture, plastic correction factors, fixture rollers, J-R resistance curve
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 0
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3. Predictive modelling of weld bead geometry in wire arc additive manufacturingKristijan Šket, Miran Brezočnik, Timi Karner, Rok Belšak, Mirko Ficko, Tomaž Vuherer, Janez Gotlih, 2025, izvirni znanstveni članek Opis: This study investigates the predictive modelling of weld bead geometry in wire arc additive manufacturing (WAAM) through advanced machine learning methods. While WAAM is valued for its ability to produce large, complex metal parts with high deposition rates, precise control of the weld bead remains a critical challenge due to its influence on mechanical properties and dimensional accuracy. To address this problem, this study utilized machine learning approaches—Ridge regression, Lasso regression and Bayesian ridge regression, Random Forest and XGBoost—to predict the key weld bead characteristics, namely height, width and cross-sectional area. A Design of experiments (DOE) was used to systematically vary the welding current and travelling speed, with 3D weld bead geometries captured by laser scanning. Robust data pre-processing, including outlier detection and feature engineering, improved modelling accuracy. Among the models tested, XGBoost provided the highest prediction accuracy, emphasizing its potential for real-time control of WAAM processes. Overall, this study presents a comprehensive framework for predictive modelling and provides valuable insights for process optimization and the further development of intelligent manufacturing systems.
Ključne besede: wire arc additive manufacturing, WA AM, predictive modelling, machine learning, weld bead geometry, XGBoost
Objavljeno v DKUM: 13.03.2025; Ogledov: 0; Prenosov: 3
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4. 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: 8
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5. Influence of microdefect on fatigue properties in weld fine grain heat affected zone on nickel molybdenum alloy steel : doctoral disertationFidan Smaili, 2023, doktorska disertacija Opis: This research presents two possibilities to prepare and test the Fine Grain of a Heat Affected Zone, which, practically, could be considered as the weakest part of welded joints in the presence of any microdefect. It is a narrow zone located between the fusion zone and the unaffected base material; therefore, only a few methods are suitable to test its mechanical properties. The 18CrNiMo7-6 steel was used as the base material. As this steel is usually used for the production of dynamically loaded components, testing of its fatigue behaviour and fracture toughness was crucial, but also measurement of its hardness and impact toughness. To investigate the mechanical properties of a Fine-Grain Heat-Affected Zone (FG HAZ), two different methods for simulation of as-welded microstructures were used in this research: A weld thermal cycle simulator (WTCS) and austenitising in a laboratory furnace +
Ključne besede: weld joint, Fine Grain Heat Affected Zone, mechanical properties, fatigue crack growth
Objavljeno v DKUM: 06.10.2023; Ogledov: 458; Prenosov: 50
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6. Application of normalization method to fracture toughness testing of welds with pronounced strength heterogeneity : doctoral disertationPrimož Štefane, 2022, doktorska disertacija Opis: This doctoral dissertation presents the results of an extensive fracture testing programme of
welds with pronounced strength heterogeneity. Purpose of this programme was to determine
fracture toughness of heterogeneous welds that contain a midplane crack. Application of
standardized fracture testing methods in heterogeneous welds might lead to overestimation or
underestimation of fracture toughness and consequentially to inaccurate assessment of
structural integrity. Reasons for that are variations in mechanical properties of different
material regions in the weld which have a significant impact on development of deformation at
the crack tip, and consequently on the crack driving force. Experimental procedures in scope
of this research include fabrication of weld sample plates, that were welded with MAG process.
The welds were fabricated using two different electrodes, one with higher and one with lower
mechanical properties, with respect to base material S690QL in order to replicate extreme
variations of mechanical properties in the weldment. Fabricated welds were then characterized
in detail using metallography, three-point bend impact testing, indentation hardness
measurements and tensile testing of flat miniature and round bar standard tensile specimens.
Resistance of welds to stable tearing was investigated by fracture testing of square surface
cracked SE(B) specimens containing a weld midplane notch. J-integral has been estimated from
plastic work, using the normalization data reduction method that is included in standard ASTM
E1820. The advantage of the normalization data reduction method is that no special equipment
or complex testing method is needed to measure ductile crack growth during fracture testing.
The ductile crack growth is determined directly from the load-displacement record, by applying
appropriate calibration function and physical lengths of initial and final cracks that were
measured post-mortem with the nine-point method. Several correction factors had to be
calibrated in order to successfully implement the normalization data reduction method to
fracture testing of welds with pronounced strength heterogeneity. For that reason, parametric
finite element analyses were conducted for several weld configurations. Finite element models
incorporated plane strain conditions in order to provide calibrated factors that comply with
plane strain equations included in ASTM E1820. Additionally, crack tip constraint has been
extensively analysed and correlated with the plastic deformation fields. This clarified altered
deformation behaviour of modelled welds in comparison with the base material and
corresponding effect on fracture toughness. Finally, calibrated factors were applied to
computation of J-integral from data that were measured during fracture testing. J-R resistance
curves were constructed for the tested heterogeneous welds and compared to the ones of the
base material. This directly showed the effect of variations of mechanical properties on the
weld fracture behaviour.
Ključne besede: weld, strength mismatch, fracture, normalization data reduction technique, plastic
correction factors, test fixture, SE(B) specimen, J-R resistance curve
Objavljeno v DKUM: 10.01.2023; Ogledov: 778; Prenosov: 202
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7. Validation of boundary element method for assessment of weld joints accounting for notch stress : magistrsko deloRok Skerbiš, 2022, magistrsko delo Opis: Robust, automated mesh generation on arbitrary weld joint geometries, using finite element method (FEM) is a problematic task. It was previously discovered, that an arbitrary weld joint geometry can be parameterized inside a CAD environment [1], however when it comes to domain discretization and boundary conditions assignment, the parameterized approach becomes too demanding inside FEM. This results in long FEM model preparation times and sometimes in problems with the parametric model itself, which leads to a need for an additional numerical method - boundary element method (BEM), which overcomes this issue and is beneficial in this case. BEM is a numerical method, that in addition to other applications finds a use in the elasto-mechanic problems, where the only concern is the boundary of the considered geometric domain. Since notch stress calculations of weld joints fall into this category, their calculation can be carried out with it. Since there is not much available information on whether or not such calculations are a suitable alternative for the currently used FEM, this thesis had to be confirmed through a structured and step by step procedure. First, a notch mesh quality study has been made, then other entities followed. It was discovered that BEM is applicable to the problem and capable of calculating results with sufficient quality. Furthermore, the parameter driven approach and automated calculation provide for additional advantageous potentials.
Ključne besede: weld joint, boundary element method, finite element method, spatial discretization, notch stress
Objavljeno v DKUM: 02.11.2022; Ogledov: 549; Prenosov: 0
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8. Weldability prediction of high strength steel S960QL after weld thermal cycle simulationMarko Dunđer, Tomaž Vuherer, Ivan Samardžić, 2014, izvirni znanstveni članek Opis: This paper presents weld thermal cycle simulation of high strength steel S960QL, and describes influence of cooling time t8/5 on hardness and impact toughness of weld thermal cycle simulated specimens. Furthermore, it presents analysis of characteristic fractions done by electron scanning microscope which can contribute to determination of welding parameters for S960QL steel.
Ključne besede: high strength steels, S960QL steel, weldability, weld thermal cycle simulation, hardness, toughness
Objavljeno v DKUM: 03.07.2017; Ogledov: 2986; Prenosov: 167
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10. Suitability of heat treatment for crack resistance of material in the connection part of heavy transporter for liquid slagTomaž Vuherer, Ljubica Milović, Milorad Zrilić, Ivan Samardžić, Vladimir Gliha, 2013, drugi znanstveni članki Opis: The post weld heat treatment (PWHT) was used to reduce the level of the residual stresses and increase of the crack resistance of the materal in the cnnection part. The article presents the results of the residual stress measurements immediately after welding and after the stress relaxation by the PWHT.
Ključne besede: weld, heat treatment, residual stress, stress relaxation, crack resistance
Objavljeno v DKUM: 03.07.2017; Ogledov: 2337; Prenosov: 104
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