Application of laser-arc hybrid welding on fabricating large steel structures such as ships and bridges are being extended. It is important to select proper welding conditions based on joint types ...and plate thickness. There are many factors in hybrid welding conditions, for example, heat inputs of laser and arc, welding speed, groove gap in butt joint, angles of laser head and arc torch, laser spot diameter and defocus, flow of shield gas etc. Especially, the heat input and welding speed affect the degree of restraint of joint which causes cold cracking. It is necessary to identify the welding conditions by which prevent the occurrence of cold cracking for extending the application of hybrid welding on fabrication of large steel structures.In this study, the occurrence of cold cracking in hybrid welding was mechanically evaluated by using a concept of restraint strain. The hybrid welding experiment was performed on different lengths of slit joints by SM490A steel with thickness of 24mm. The welding conditions such as heat input from each heat source and welding speed were variously changed. The relationship between cold cracking occurrence and the average restraint strain calculated by a 3D thermal elastic plastic analysis. Among the welding conditions adopted in this study, the criterion of cold crack occurrence might exist between 1.7% and 6.4% of the average restraint strain. Furthermore, an estimation method for average restraint strain based on the welding conditions was proposed. It might be useful for simply evaluating the occurrence of cold crack without performing the precise thermal elastic plastic analysis.
Heat treatment of wood appears as an ecological and environmentally friendly alternative in the field of wood treatment. Generally, thermal modification increase dimensional stability by reduces of ...hygroscopicity and water absorption but it makes it difficult to bonding in some application. During welding, changes in the morphological, chemical, and physical properties of the wood cell wall are observed due to the compression and high temperatures produced by welding. Also, the degradation of cell wall in the wood causes some mechanical properties are reduced. This modification appears without any effect on the linear welding of thermal-ash wood. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) were used for evaluation of properties of wood-welding systems and their interactions. The mass spectrometry (MS) analysis was used to identifying the organic degradation products emitted during welding of thermo-ash. The results of experiments show that the use of friction welding for the bonding of thermal ash wood in dry conditions was possible, and we had good results. The best combination was with a welding time of 3.5 s devised to 0.5 s and 3 s and welding pressure 2.5 and 4 MPa, respectively. The result obtained is comparable to the result obtained with EPI adhesives. Welding time greater than 3.5 MPa negatively affects the welding quality and gives low the mechanical strength.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Microstructural and mechanical properties of friction stir welded copper plates under different welding parameters including various transitional and rotational speed of tool and number of passes ...under argon as protective gas have been investigated in the present study. This research cleared that owing to the occurrence of recrystallization phenomenon in stir zone, fracture toughness and Vickers hardness can increase by 39.1% and 45.1% relative to base metal, respectively. While, occurrence of annealing phenomenon in HAZ leads to a downfall in microstructural and mechanical properties. Namely, the Vickers hardness 15.8%, the tensile straight 36.1% and the fracture toughness 14.3% decrease relative to the base metal. Furthermore, this study showed that for obtaining a better weld, it is suggested to perform the welding process in a condition that leads to lower heat transformation to workpiece instead of performance of two or more welding passes. Finally, it was cleared that the different conditions including rotational and transitional speed of tool and also, the number of welding passes can affect the amount of transferred heat to the workpiece, therefore, they can affect the microstructural and mechanical properties of obtained welds.
This work presents a study of mechanical properties of the wood end-grain welding of spruce wood. The shear properties of butt joints of spruce at different pressure and welding time were studied.
...Between all the parameters of spruce welding, the welding pressure is one of the most important in relation to the mechanical properties. Thus, a good joint strength was obtained for spruce wood at high pressure. An increase of shear strength is observed with an increase in welding pressure. It is clear that at high pressure the welded material becomes more rigid and this is also coupled to the to the more extensive condensation reaction of lignin.
The defibration tendency in end-grain-to-end-grain welding indicates that wood spruce welding is possible and yields sufficient joint strength. The welded interphase in end-grain-to-end-grain spruce welding appears possible and gives a joint with an anatomical appearance of a “natural” fingerjoint. Such “natural” fingerjoints can give equivalent than glued fingerjoints.
The advantages of the end-grain-to-end-grain welding are then the very short time of processing, the dispensation of preparing the fingerjoint profiles and to avoid the use of adhesives.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this study, the effect of welding conditions on the opening and closing behavior of root gap during butt-welding was systematically investigated through the use of thermal elastic-plastic finite ...element analysis. The foci of welding conditions were weld heat input per unit weld length and plate thickness, welding speed, plate width and thickness ratio of weld metal to base metal. And then, parameters of dimensionless transverse temperature distribution to width and mechanical melting length behind weld heat source were derived respectively from weld thermal conduction theory for evaluating the root gap behavior during butt-welding. As the results, it has been clarified that the root gap behavior during butt-welding is dependent on the proposed two parameters in both single layer butt-welding and first layer butt-welding of thick plates. Also, the closing behavior of root gap is conceivable in the abstract when both of parameters becomes sufficiently-small, but in reality difficult to occur in single layer butt-welding because elements of weld metal remains unmelted. Meanwhile, the closing behavior of root gap becomes that much easier to occur in first layer butt-welding of thick plates because both parameters are possible to be sufficiently-small. Thus, more detailed understanding of opening and closing behavior during butt-welding, which can explain the cause of the differences in root gap behavior in previous studies, has been obtained.
► The efficient welding conditions in MPW rather depend on gap increase than on charging voltage variation. ► The size of the weld given by a torsion-shear test reveals the weld quality. ► There is ...an optimum range of the gap giving a high weld size. ► The low and high gaps are detrimental to the integrity of the welded assembly.
This study investigates the experimental research of the appropriated conditions for the magnetic pulse welding of AA6060T6 tubular assembly. Some welding tests were performed with two process parameters: the charging voltage and the width of the air gap between the two parts to be welded. A torsion-shear test, associated with the material fracture surfaces observation, gives an insight about the appropriateness of the welding conditions. The failure mode of the destructive test gives a dimensional criterion of the weld that is used as weld quality. It appears that the voltage does not strongly affect the weld quality for a low gap. It is possible to find an optimal gap range giving a high weld length. When the gap is too small, it is necessary to increase the pressure on the flyer, and some cracks appear in the material. Similarly, when the gap is too large, the high impact energy damages the welded interface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Mass transfer has been studied at atomic scale by molecular dynamics simulation of friction stir welding and vibration-assisted friction stir welding using the modified embedded atom potential. It ...was shown that increasing the velocity movement and decreasing the angle velocity of the tool reduce the penetration depth of atoms into the opposite crystallite in the connected pair of metals. It was shown also that increasing the amplitude of vibrations applied to the friction stir welding tool results in increasing the interpenetration of atoms belonging to the crystallites joined
An analysis of the quality of the thick-walled S355J2+N steel welded joint used most frequently in the general-building, power and other contemporary steel constructions is presented in the following ...article. A process of examining welding technologies was made on the tick-walled butt joints of plates by using the MAG – 135 welding method. The aim of the discussed topic was to optimize the process of welding thick-walled welded joints due to their mechanical strength properties and efficiency.
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