1. Comparison of three methods of measuring residual stresses in welded joints of high-strength steel S960QLMirza Manjgo, Gorazd Lojen, Nenad Gubeljak, Blaž Karpe, Tomaž Vuherer, 2024, izvirni znanstveni članek Opis: The influence of residual stresses as a result of the welding process in the overall stress state of the weld joint is of great importance because they significantly affect the creation and growth of cracks, the occurrence of brittle fracture, and material fatigue. Previous experiences indicate that it would be necessary to provide an assessment of the deformation and stress state in the critical zones of the weld joints using a suitable test method, which will not endanger the structural integrity of the tested places. There are different methods for measurement of residual stress in welded constructions: destructive, semi-destructive and non-destructive. To choose one method over another, it is necessary to take into account the advantages and limitations of these techniques for practical application. This paper considers and analyzes the residual stresses in the welded joint of high-strength steel S960QL. MAG welding was performed by a robot. Three methods were used to measure the residual stresses: the magnetic method (MAS), the X-ray diffraction method (XRD), and the hole drilling method (HD). By all three methods, the highest residual stresses were measured in the weld metal and in the heat-affected zones. Nevertheless, the measured values differed considerably. The differences can be contributed to (a) the kind of stress that the individual method measures, (b) to the volume of material from which each method captures the signal and averages it, and (c) to the different sensitivities of the applied methods to coarse-grained microstructure and microstructural gradients. Ključne besede: welded joints, high-strength steel, residual stress, magnetic method, X-ray diffraction method, hole drilling method Objavljeno v DKUM: 11.06.2025; Ogledov: 0; Prenosov: 3
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2. Numerical simulation of fatigue crack growth and fracture in welded joints using XFEM—a review of case studiesAleksandar Sedmak, Aleksandar Grbović, Nenad Gubeljak, Simon Sedmak, Nikola Budimir, 2024, pregledni znanstveni članek Opis: Numerical simulation of fatigue crack growth in welded joints is not well represented in the literature, especially from the point of view of material heterogeneity in a welded joint. Thus, several case studies are presented here, including some focusing on fracture, presented by two case studies of mismatched high-strength low-alloyed (HSLA) steel welded joints, with cracks in the heat affected zone (HAZ) or in weld metal (WM). For fatigue crack growth, the extended finite element method FEM (XFEM) was used, built in ABAQUS and ANSYS R19.2, as presented by four case studies, two of them without modelling different properties of the welded joint (WJ). In the first one, fatigue crack growth (FCG) in integral (welded) wing spar was simulated by XFEM to show that its path is partly along welded joints and provides a significantly longer fatigue life than riveted spars of the same geometry. In the second one, an integral skin-stringer panel, produced by means of laser beam welding (LBW), was analysed by XFEM in its usual form with stringers and additional welded clips. It was shown that the effect of the welded joint is not significant. In the remaining two papers, different zones in welded joints (base metal—BM, WM, and HAZ) were represented by different coefficients of the Paris law to simulate different resistances to FCG in the two cases; one welded joint was made of high-strength low-alloyed steel (P460NL1) and the other one of armour steel (Protac 500). Since neither ABAQUS nor ANSYS provide an option for defining different fatigue properties in different zones of the WJ, an innovative procedure was introduced and applied to simulate fatigue crack growth through different zones of the WJ and evaluate fatigue life more precisely than if the WJ is treated as a homogeneous material. Ključne besede: fatigue crack growth, extended finite element method, welded joints, fatigue life, highstrength low-alloyed steel Objavljeno v DKUM: 25.11.2024; Ogledov: 0; Prenosov: 8
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3. Fracture toughness of HSLA welds made on penstock materialZdravko Praunseis, 2019, izvirni znanstveni članek Opis: The presence of different microstructures along the pre-crack fatigue front has a significant effect on the critical crack tip opening displacement (CTOD). This value is the relevant parameter for the safe servicing of welded structures (penstocks). In the case of specimens with the through-thickness notch partly in the weld metal, partly in the heat-affected zone, and partly in the base material, i.e., using the composite notched specimen, the fracture behaviour significantly depends on the portion of the ductile base material, the size, and the distribution of mismatching factor along the vicinity of the crack front. Ključne besede: High Strength low Alloyed Steel, CTOD Fracture Toughness Testing, CTOD-R resistance Curve, Welded joints Objavljeno v DKUM: 22.12.2023; Ogledov: 614; Prenosov: 175
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4. The influence of delta ferrite on the quality assessment of austenitic stainless steel welds for the production of ovensZdravko Praunseis, 2020, izvirni znanstveni članek Opis: Rust-resistant metals, such as the popular stainless steel, often contain some quantities of delta ferrite that lower the mechanical properties of welded joints. The results of the study show that the amount of ferrite influences the quality assessment of austenitic stainless steel welds for the production of ovens using the resistance seam welding process. In this article, the basic device of resistance seam welding for the production of stainless steel welds is described. The device itself will have a significant role in the operation of the line; therefore, it was very precisely constructed and designed. Ključne besede: austenitic stainless steel, delta ferrite, quality assessment, welded joints, production of ovenss Objavljeno v DKUM: 15.11.2023; Ogledov: 421; Prenosov: 49
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5. Quality assessment of single-pass corner steel welded jointsZdravko Praunseis, Bojan Stergar, Iztok Brinovar, 2021, izvirni znanstveni članek Opis: The aim of this paper is to analyse the quality assessment of single-pass corner steel welded joints. The testing revealed the most burdened welded joints, which were cut out of the workpiece and prepared for metallographic macroscopic and microscopic analysis. Thus, for all examinations of single-pass corner steel welded joints, the standard test procedures were used to determine the weldability and quality assessment of base materials and welded joints. Additionally, the effects of various welded defects of single-pass weld material on the bearing strength of corner welded joints will be analysed. Ključne besede: welded joints, microstructure, cracks, undercut, main frame Objavljeno v DKUM: 13.11.2023; Ogledov: 399; Prenosov: 44
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7. Fatigue crack initiation from microstructurally small Vickers indentationsTomaž Vuherer, Andrej Godina, Zijah Burzić, Vladimir Gliha, 2007, izvirni znanstveni članek Opis: The resistivity of coarse grain steel against crack initiation in the presence of micro defects is discussed. Samples of material with martensitic microstructure were prepared by adequate thermal treatment. Microstructurally small Vickers indentations were used as an artificial micro defect. The compressive residual stresses are due to the irreversibility of plastic deformation. The moment of indenting enables to prepare samples with and without effects of residual stresses. The stress level for crack initiation depends on the actual indentation size. The location of initiated cracks is affected by the presence and character of residual stresses. Ključne besede: welded joints, micro defect, coarse grain HAZ, crack initiation, crack growth, stress concentration, fatigue limit, Vickers, residual stresses Objavljeno v DKUM: 03.07.2017; Ogledov: 1782; Prenosov: 126
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8. Charpy toughness of vibrated microstructuresBogdan Pučko, Vladimir Gliha, 2005, izvirni znanstveni članek Opis: The aim of this study was to investigate the influence of vibration on impact toughness of weld metal. Studies were carried out on two welds, of which one had been welded with applying vibration during welding. From test plates samples were made to simulate heat affect in combination with or without vibration after solidification. In this way conditions at multi-pass welding were simulated. According to different conditions Charpy toughness on non standard specimens and fracture appearance were observed. Vibration during welding benefits impact energy of weld metal, especially if weld metal undergoes further heatb treatment. Ključne besede: welded joints, impact toughness, vibration, Charpy toughness, SAW Objavljeno v DKUM: 03.07.2017; Ogledov: 1109; Prenosov: 118
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9. Factors influencing the yielding constraint by cracked welded componentsDražan Kozak, Jelena Vojvodič-Tuma, Nenad Gubeljak, Damir Semenski, 2005, izvirni znanstveni članek Opis: The effect of strength mismatch for welded joints performed with different geometries on the yielding constraint has been investigated in the context of single-edged fracture-toughness specimens subjected to bending SE(B) using the finite-element method. The crack was located in the centre of the weld. Two geometri cal parameters have been identified as being the most important: the crack-Iength ratio a/W and the sIenderness of the welded joint (W-a)/H. They were systematically varied as follows: a/W = 0.1; 0.2; 0.3; 0.4; 0.5 and W = 2H, 4H, 8H, 16H, 24H. Basic equations and plane-strain finite-element solutions for the overmatched SE(B) specimen with all configuration combinations are given. The results are in good agreement with those in literature. This paper aims to establish yield-Ioad solutions for the same weldment configurations, but with materials dissimilarity present within the weld. This situation is usually encountered during repair welding. For this purpose, a practical combination of filler materials, with the same portion of overmatched part with M = 1.19 and undermatched part with M = 0.86, has been selected. Plane-strain solutions for the heterogeneous weld with the cracklocated in the overmatched half were obtained. The influence of the yielding-constraint key parameters has al so been evaluated. Yield-Ioad results for the specimens performed with different weld widths have the greatest scattering for the a/W = 0.5. The transition from the overmatched to the undermatched solution with increasing H is evident. On the other hand, the behaviour of the specimen with a shallow crack is dictated by the overmatch region ahead of the crack tip and depends very little on the weld slenderness. An approximated 3-D area of the yield-Ioad solutions depending ona/W and (W-a)lH has been proposed. Furthermore, the stress triaxility parameter h has been calculated using 2-D and 3-D finite-element analysis, and given as a field in the spec imen to get an insight into yielding-constraint regions. It was found that the 3-D yield-Ioad solutions are very close to the plane-strain solutions. Also, the effect of a/W on the yielding constraint is more significant than the effect of Mand (W-a)/H. Ključne besede: welded structures, welded joints, fracture mechanics, cracks, SE(B) specimens, yielding load, yielding constraint parameters Objavljeno v DKUM: 06.04.2017; Ogledov: 1488; Prenosov: 122
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