1. Influence of kinematic factors of friction stir welding on the characteristics of welded joints of forged plates made of EN AW 7049 A aluminium alloyMilenko Perović, Sebastian Baloš, Dražan Kozak, Darko Bajić, Tomaž Vuherer, 2017, izvirni znanstveni članek Opis: In this paper, the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminium alloy is studied. Rotation speed was varied from 750 min−1 to 850 min−1 and welding speed from 60 mm/min to 80 mm/min. It was found that the energy of crack propagation is up to three times higher than the energy of crack initiation. This ratio was found by testing the Charpy notched specimens taken from left and right from the weld centre, 4 mm from the notch in a direction opposite to a direction of welding. Micro hardness distribution in the nugget does not show large dissipation of value regardless if the measuring point is in the upper or lower section of the nugget. Weld microstructure characteristics and zones are clearly defined at the basis of grain size and material flow.
Ključne besede: dynamic recrystallization, friction stir welding, impact strength, micro hardness distribution
Objavljeno: 12.07.2017; Ogledov: 616; Prenosov: 285
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2. 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: 03.07.2017; Ogledov: 2054; Prenosov: 100
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5. Prediction of the hardness of hardened specimens with a neural networkMatej Babič, Peter Kokol, Igor Belič, Peter Panjan, Miha Kovačič, Jože Balič, Timotej Verbovšek, 2014, izvirni znanstveni članek Opis: In this article we describe the methods of intelligent systems to predict the hardness of hardened specimens. We use the mathematical method of fractal geometry in laser techniques. To optimize the structure and properties of tool steel, it is necessary to take into account the effect of the self-organization of a dissipative structure with fractal properties at a load. Fractal material science researches the relation between the parameters of fractal structures and the dissipative properties of tool steel. This paper describes an application of the fractal dimension in the robot laser hardening of specimens. By using fractal dimensions, the changes in the structure can be determined because the fractal dimension is an indicator of the complexity of the sample forms. The tool steel was hardened with different speeds and at different temperatures. The effect of the parameters of robot cells on the material was better understood by researching the fractal dimensions of the microstructures of hardened specimens. With an intelligent system the productivity of the process of laser hardening was increased because the time of the process was decreased and the topographical property of the material was increased.
Ključne besede: fractal dimension, fractal geometry, neural network, prediction, hardness, steel, tool steel, laser
Objavljeno: 17.03.2017; Ogledov: 849; Prenosov: 78
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6. Characterization of heterogeneous arc welds through miniature tensile testing and Vickers-hardness mappingStjin Hertelé, Jonas Bally, Nenad Gubeljak, Primož Štefane, Patricia Verleysen, Wim De Waele, 2016, izvirni znanstveni članek Opis: The heterogeneity of arc-welded connections is often ignored in structural assessments, giving rise to inaccuracies. Improved assessments taking into account heterogeneity require the characterization of local constitutive properties. We have compared two methods to do this: Vickers-hardness mapping and miniature tensile testing. Whereas the former is more straightforward to apply, the latter provides full-range stress-strain data. This paper discusses an experimental comparison of both methods on a heterogeneous arc weld. Miniature tensile tests were performed, using digital image correlation to measure the strain. The specimens were indented to compare their stress-strain response with Vickers hardness. Notwithstanding that small natural flaws invalidated some tests, reliable stress-strain curves were obtained. Vickers hardness testing is a convenient alternative if the yield and ultimate tensile strength are the only points of interest and the corresponding conversion inaccuracy is acceptable.
Ključne besede: arc weld, heterogeneity, hardness, miniature tensile testing, digital image correlation
Objavljeno: 14.03.2017; Ogledov: 586; Prenosov: 303
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7. The fracture behaviour of global/local mis-matched weld joints provided on HSLA steelsInoslav Rak, Nenad Gubeljak, Zdravko Praunseis, 2001, izvirni znanstveni članek Opis: The fracture behaviour of thick section high strength steel weldments, that contain soft root passes, has been studied. Two different weld consumables with different strength mismatch (1>M>1) and fracture toughness properties in the WM have significantly increased the complexity of the mis-match effect and failure behaviour of weld joints, depending on the crack location and the thickness of the soft root layer. The aim was to explain the effect of strength heterogeneity between BM and WM and between different regions in WM (global/local mismatching). R-curves of WM and HAZ regions were also discussed. The conclusion is that the application of a welding procedure with a two-pass soft root layer, introduced for the purpose of reducing or even omitting preheating, can be recommended in mis-matched weld joints on steel grade HT80. Nevertheless, the alloying from BM, and the tempering effect of subsequent weld passes, have to be taken into account. They can cause reduction of the root region ductility and affect the local mismatch in WM and HAZ. The deterioration by providing a soft root layer can probably be reduced by a selected consumable and proper welding procedure. The final conclusion is that the application of a mismatched weld joint with a soft root layer can be recommended only if high root toughness can be provided.
Ključne besede: welding, welded joints, strength mismatching, fracture toughness, CTOD, hardness, impact toughness, HSLA steels
Objavljeno: 01.06.2012; Ogledov: 1439; Prenosov: 99
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8. Effect of vibration on weld metal hardness and toughnessBogdan Pučko, Vladimir Gliha, 2005, izvirni znanstveni članek Opis: Vibration of welded parts is usually applied to achieve effects similar to thermal stress relief. With vibration, it is not only residual stresses that are affected. Using two different welding processes, the influence of vibration on hardness and toughness of the weld was measured. For each weldingprocess, two series of Charpy specimens were made over the temperature range from -60 to +20°C. The only difference between the two series was in performing welding with or without vibration. Slight differences in weld metalhardness were observed. Toughness measurements show an increase in impacttoughness and a significant increase in fracture toughness in samples which were vibrated during welding.
Ključne besede: welding, welded joints, residual stresses, vibrational stress relief, hardness, toughness, steel
Objavljeno: 01.06.2012; Ogledov: 1691; Prenosov: 78
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9. Weldability investigation of TStE 420 after weld thermal cycle simulationMarko Dunđer, Tomaž Vuherer, Ivica Kladarić, 2010, izvirni znanstveni članek Opis: The paper presents a short description and overview of the weld thermal cycle simulation methods. An experimental investigation on the weld cycle simulated specimens is predicted by a plan of experiment using single cycle simulation. The obtained hardness results are compared with double cycle simulated specimens results of individual points in the heat-affected zone. Beside that, the characteristic microstructures of points in the heat-affected zone after a single weld thermal cycle simulation are given. A thermal simulation method is suitable for different weldability examinations. In this paper, the authors would like to investigate the maximal hardness of individual points in the weld joint what is important when considering cold cracking sensitivity.
Ključne besede: HSLA steels, weldability, weld thermal cycle simulation, hardness
Objavljeno: 31.05.2012; Ogledov: 1079; Prenosov: 24
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