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The influence of simulated thermal cycle on the formation of microstructures of multi-pass weld metal
Danilo Rojko, Vladimir Gliha, 2005, izvirni znanstveni članek

Opis: The influence of weld thermal cycle on the micrstructural changes in weld metal by use of the simulated microstructures. We examined the kinetics of the formation of austenite from the starting microstructure. The simulated microstructures were prepared by the application of simulated thermal cycles with different peak temperatures on a sample of real single-pass weld metal. The reproduction of thermal cycles were carried out by the SMITWELD simulator. Special attention was dedicated to the influence of thermal cycle on the formation of microstructures, which can be potential triggers of brittle fracture (local brittle zones).
Ključne besede: welding, welded joints, multi-pass weld metal, simulated microstructure, impact toughness
Objavljeno: 03.07.2017; Ogledov: 1581; Prenosov: 81
.pdf Celotno besedilo (223,13 KB)
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Fatigue crack initiation from microstructurally small Vickers indentations
Tomaž 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: 03.07.2017; Ogledov: 703; Prenosov: 85
.pdf Celotno besedilo (1,02 MB)
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Charpy toughness of vibrated microstructures
Bogdan 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: 03.07.2017; Ogledov: 504; Prenosov: 82
.pdf Celotno besedilo (118,79 KB)
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Factors influencing the yielding constraint by cracked welded components
Dražan 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: 06.04.2017; Ogledov: 876; Prenosov: 75
.pdf Celotno besedilo (793,79 KB)
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Weld joint fracture behaviour of HSLA steels dissimilar in strength
Inoslav Rak, Arpad Treiber, 1998, izvirni znanstveni članek

Opis: The effect of strength differences (mismatch) between weld metal and two base metals as well as local variations of strength within weld metal/HAZ zones on the toughness properties were discussed. The significance of local fracture toughness measurement technique was also discussed by comparing the CTOD results of [delta]5 and British Standard [delta]BS. Some differences between the two techniqes were discussed in particular for CGHAZ toughness of similar and dissimilar joints.
Ključne besede: welding, welded joints, fracture mechanics, HSLA steels, fracture toughness
Objavljeno: 10.07.2015; Ogledov: 859; Prenosov: 24
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Microstructural investigation of the heat-affected zone of simulated welded joint of P91 steel
Tomaž Vuherer, Marko Dunđer, Ljubica Milović, Milorad Zrilić, Ivan Samardžić, 2013, izvirni znanstveni članek

Opis: In the process of testing real components exposed to elevated temperature, it is not possible to neglect cracks. The most significant cracks can be induced by welding, which is applied for joining of structural components. Pressure equipment in service is also exposed to high pressure and high stresses. Materials for their manufacturing are designed to resist high stressat elevated temperature, and to meet requirements regarding creep resistance. The objective of this study is to investigate microstructure of different regions of the heat affected zone in T/P91 steels by using thermal simulation instead of welding.
Ključne besede: welded joints, microstructures, P91 steel, heat-affected zone, heat treatment
Objavljeno: 10.07.2015; Ogledov: 636; Prenosov: 128
.pdf Celotno besedilo (921,38 KB)
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The transferability of fracture-mechanics parameters to fracture performance evaluation of welds with mismatching
Masao Toyoda, Zdravko Praunseis, 2000, izvirni znanstveni članek

Opis: 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.
Ključne besede: welding, welded joints, strength mismatching, plastic constraint, transferability concept
Objavljeno: 01.06.2012; Ogledov: 1545; Prenosov: 321
.pdf Celotno besedilo (802,24 KB)
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The fracture behaviour of global/local mis-matched weld joints provided on HSLA steels
Inoslav 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: 1485; Prenosov: 102
.pdf Celotno besedilo (441,77 KB)
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Strength mismatch effect on yield load in X-shaped weldment with centre crack
Dražan Kozak, Nenad Gubeljak, Jožef Predan, Franjo Matejiček, 2004, objavljeni znanstveni prispevek na konferenci

Opis: This paper provides yield load solutions for single edged fracture toughness specimen subjected to bending SE (B) with present X-shaped weld joint. The weld centre crack is located in the overmatch weld part. The corresponding fully plastic yield loads were obtained directly by plain strain FEM analysis for five characteristic a/W ratios: 0,1;0,2;0,3;0,4 and 0,5. Also, the influence of the sistematically varied weld root width 2H on the fracture behaviour has been evaluated. It was found that yield load decreases with the increasing weld root, because the undermatched region ahead the crack tip plays the dominant role.
Ključne besede: fracture mechanics, X-shaped welded joints, centre crack, strength mismatching, plastic yield load, constraint effects
Objavljeno: 01.06.2012; Ogledov: 1251; Prenosov: 30
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Micromechanical analysis of constraint effect on fracture initiation in strength mis-matched welded joints
Miloš Dobrojević, Marko Rakin, Nenad Gubeljak, I. Cvijović, Milorad Zrilić, N. Krunich, Aleksandar Sedmak, 2007, izvirni znanstveni članek

Opis: In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect crack growth initiation in mismatched welded joints. The single edged- notched bend specimens (precrack length ▫$a_o/W=0.32$▫) were experimentally and numerically analysed. The coupled micromechanical model prposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18 mm). HSLA steel was used as the base metal in a quenched and tempered condition. The flux-cored arx-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smmoth specimen. The difference in fracture behaviour between over- and undermatched welded joints obtained in experimental results was followed by numerical computationsof void volume fraction in front of the crack tip.
Ključne besede: fracture mechanics, ductile fracture, high strength low alloyed steel, cracks, micromechanical model, mismatched welded joints, constraint effect, void growth
Objavljeno: 01.06.2012; Ogledov: 1450; Prenosov: 77
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