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2.
Charpy toughness and microstructure of vibrated weld metal
Bogdan Pučko, Vladimir Gliha, 2006, original scientific article

Abstract: Vibration during welding can be used to obtain certain changes in mechanical properties of weld metal. Research work on the influence of vibration on the secondary microstructure of welds and hence on the Charpy toughness was performed. Vibration during welding exhibits positive effects on the microstructure constituent formation. Multipass welding was simulated with reheating of the original single pass weld in order to obtain similar microstructure to multipass welds. Microstructures were examined with an optical microscope. Additionally, fractographic examination of the rupture of Charpy specimens was performed. Changes in the microstructure according to vibration were observed which affect toughness of the weld metal. Vibration during welding was rated more effective in the case of reheating the weld metal, which is the case in multipass welding.
Keywords: welding, welded joints, mechanical properties of metals, ferrite, vibration, microstructure, toughness, notched bar testing, weld metal
Published: 31.05.2012; Views: 1404; Downloads: 63
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3.
The effect of small flaws on the fatigue strength of HAZ at the weld toe
Vladimir Gliha, 2007, original scientific article

Abstract: The effects of small artificial surface flaws on the fatigue strength of HAZ material are studied. The samples of coarse grain HAZ material were prepared using a welding thermal-cycle simulator. The artificial flaws were produced byindenting with a Vickers pyramid at different loads as either single indentations or as a series. The size of the flaws did not exceed the primary austenitic grain size of the material, which is the most relevant microstructural unit of carbon steels. The dependence of the experimentally determined bending fatigue strength of treated coarse grain HAZ materials on the properly evaluated size of the artificial flaws was compared with the law of long-crack propagation. The biggest flaws evaluated with the flaw-size parameter ?area ? 100 m are still small for the studied coarse grain HAZ. In further experimental work, the effects of flaw size and the effects of residual stresses should be analysed separately.
Keywords: welding, welded joints, coarse grained HAZ, crack initiation, flaw-size parameter, small surface flaws, stress intensity range, Vickers indentation, weld toe
Published: 31.05.2012; Views: 1037; Downloads: 39
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4.
Fuzzy logic based quality monitoring in short-circuit gas metal arc welding
Marjan Golob, Arpad Köveš, 2007, original scientific article

Abstract: Conventional methods, e.g. destructive and non-destructive testing methods, are expensive and time-consuming; therefore, possibilities of online and automated quality control of a welding process during welding as such are investigated. The paper deals with the possibilities of application of fuzzy logic to the analysis of weld quality, particularly assessment of the weld surface condition by means of measurable electric signals emitted during welding. A simple fuzzy inference system was realised which could relatively efficiently assess the weld quality on the basis of time variations of the welding voltage and short-circuit time in a certain time window.
Keywords: fuzzy systems, fuzzy logic, gas metal arc welding, GMAW, quality monitoring, statistical analysis, quality control, weld quality
Published: 31.05.2012; Views: 1004; Downloads: 65
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5.
Effect of vibration on weld metal hardness and toughness
Bogdan Pučko, Vladimir Gliha, 2005, original scientific article

Abstract: 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.
Keywords: welding, welded joints, residual stresses, vibrational stress relief, hardness, toughness, steel
Published: 01.06.2012; Views: 1339; Downloads: 54
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6.
Suspectibility to hydrogen induced cracking of weld beads on high-strength structural steel
Jadranka Malina, Ivan Samardžić, Vladimir Gliha, 2005, original scientific article

Abstract: We study the hydrogen embrittlement and rupture of specimens of high-strength low-alloy steel with weld beads subjected to hydrogenation under the conditions of cathodic polarization. The specimens fail in the heat-affected zone on the boundary between the main metal and the weld bead in the zone of application of the latter and, especially, near its end. This explained by a higher hardness of the metal in this zone caused by the specific features of the temperature field formed in the process of welding.
Keywords: welding, welded joints, materials, structural steel, cracking, hydrogen
Published: 01.06.2012; Views: 911; Downloads: 17
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7.
Assessment of the load-bearing capacity of a primary pipeline
Nenad Gubeljak, Jelena Vojvodič-Tuma, Borivoj Šuštaršič, Jožef Predan, Maks Oblak, 2007, original scientific article

Abstract: High-alloyed Cr-Ni-based two-phase stainless steel (SS) cast alloys are commonly used in nuclear power plants. The mechanical equipment in these facilities can contribute to a reduction in its resistance to stable crack growth as a result of extended operating times and high temperatures. The toughness of these materials strongly depends on their delta (▫$/delta$▫) ferrite content, which spinodally decomposes into two phases with different ratios of Cr and Ni at a relatively low (slightly above 300 °C) temperature. This temperature is similar to the operating temperature of the vital parts, for example, the coolant system. The formation of two phases with the same crystalstructure but different lattice parameters causes internal elastic stresses that result in a hardness increase and an impact-toughness decrease. The result is an increased risk of crack formation in the stress-concentration zones such as the critical regions of different welded joints (e.g. "L, T, K and X" shapes). The values of the critical stress intensity factor change according to its position along the crack contour. Therefore, the aim of our study was to assess the influence of the materials' changes on the crack extension and the decrease of the primary pipeline's bearing capacity by taking account of the increased temperature and time of operation for the given loading conditions. The SINTAP (European Structural Integrity Assessment Procedure) was used for this assessment.
Keywords: welding, welded joints, pipelines, fracture toughness testing, structure integrity assessment procedure
Published: 01.06.2012; Views: 998; Downloads: 47
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8.
The fracture behaviour of global/local mis-matched weld joints provided on HSLA steels
Inoslav Rak, Nenad Gubeljak, Zdravko Praunseis, 2001, original scientific article

Abstract: 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.
Keywords: welding, welded joints, strength mismatching, fracture toughness, CTOD, hardness, impact toughness, HSLA steels
Published: 01.06.2012; Views: 1181; Downloads: 58
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9.
Vloga in nastanek mikrostrukturnih sestavin M-A v zvarnih spojih maloogljičnih visokotrdnostnih konstrukcijskih jekel
Zdravko Praunseis, Masao Toyoda, Alojz Križman, Mitsuru Ohata, 2001, review article

Abstract: The existence of martensite-austenite constituents in the weld metal and heat-affected zone seriously reduces the fracture toughness of the welded joint. Therefore, we have investigated the formation of the martensite-austenite constituents when high-strength low-alloy steel is welded with a high heat input or using multi-pass welding. This paper deals with the effects of martensite-austenite constituents on the fracture toughness, the metallurgical features of the martensite-austenite constituents, and the prevention and elimination of the martensite-austenite constituents in the welded joints.
Keywords: arc welding, high-strength low-alloy steels, microstructure, martensite-austenite constituents, weld metal, heat-affected zone, cooling rate
Published: 01.06.2012; Views: 1101; Downloads: 57
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10.
The transferability of fracture-mechanics parameters to fracture performance evaluation of welds with mismatching
Masao Toyoda, Zdravko Praunseis, 2000, original scientific article

Abstract: The differences in the mechanical properties between different weld-metal regions obviously affect the strain distribution around the crack tip during a fracture test and hence influence the fracture toughness value. The variation in plastic constraint during fracture mechanics testing has an additional effect on the ductile and brittle fracture initiation behaviour of any weld joint. This paper deals with the transferability of fracture toughness results to the fracture performance evaluation of the strenght of mismatch welded joints based on the two-parameter criterion and the local approach. It was found that the numerical simulations based on the transferrable fracture concept are effective in practice.
Keywords: welding, welded joints, strength mismatching, plastic constraint, transferability concept
Published: 01.06.2012; Views: 1098; Downloads: 171
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