• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.354-366
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• 2020

This work mainly focuses on determination of the fully plastic J-integral solutions for welded center cracked plates subjected to remote tension loading. Detailed three-dimensional elasticeplastic Finite Element Analyses (FEA) were implemented to compute the fully plastic J-integral along the crack front for a wide range of crack geometries, material properties and weld strength mismatch ratios for 900 cases. According to the database generated from FEA, Back-propagation Neural Network (BPNN) model was proposed to predict the values and distributions of fully plastic J-integral along crack front based on the variables used in FEA. The determination coefficient R2 is greater than 0.99, indicating the robustness and goodness of fit of the developed BPNN model. The network model can accurately and efficiently predict the elastic-plastic J-integral for weld centerline crack, which can be used to perform fracture analyses and safety assessment for welded center cracked plates with varying strength mismatch conditions under uniaxial loading.

• International journal of advanced smart convergence
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• 제4권1호
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• pp.145-153
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• 2015

Friction Stir Welding (FSW) is a solid state welding that could successfully weld the difficult-to-weldmaterials such as an aluminum alloy. In this welding process, the stirrer of the welding tool is one of the important factors for producing the perfect sound joint that indicates the higher joint strength. So, this report aims to apply the friction stir welding using various stirrer geometries to weld the AA6063-T1 aluminum alloy butt joint, investigates the mechanical properties of the joint and then compares the mechanical properties with the microstructure of the joint. An experiment was started by applying the friction stir welding process to weld a 6.3 mm thickness of AA6063-T1 aluminum alloy butt joint. A study of the stirrer geometries effect such as a cylindrical geometry, a cone geometry, a left screw geometry and a right screw geometry at a rotational speed of 2000 rpm and a welding speed of 50-200 mm/min was performed. The mechanical properties such as a tensile strength and a hardness of the joint were also investigated and compared with the microstructure of the joint. The results are as follows. A variation of FSW Stirrer shape directly affected the quality AA6063-T1 aluminum alloy butt joint. A cylindrical stirrer shape and a cone stirrer shape produced the void defect at the bottom part of the weld metal and initiated the failure of the joint when the joint was subjected to the load during the tensile test. Left and right screw stirrer shapes gave the sound joint with no void defect in the weld metal and affected to increase the joint strength that was higher than that of the aluminum base metal.

• 한국레이저가공학회지
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• 제7권2호
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• pp.19-26
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• 2004

The effect of shield gas on the weldability, mechanical properties and formability of CO2 laser weld joint in 600MPa grade high strength steel was investigated. Bead on plate welds were made under various welding speed and shield gas. Tensile test was carried out under the load of perpendicular and parallel direction to the weld line, Formability of the joint was evaluated by Erichsen test. As the welding speed increases, the porosity fraction decreases. The porosity fraction in the joint used Ar-$50\%He$ mixed gas as a shield gas was lower than that of the joint used Ar gas. Hardness at the weld metal of full penetrated joint was nearly equal to that of water quenched raw metal. In a tensile test under a perpendicular load to the weld axis, strength and elongation of joint produced by optimum condition were nearly equal to those of base metal. However, the strength of joint in a tensile test under a parallel load to weld axis was higher than that of raw metal, but the elongation of joint was lower than that of raw metal. Elongation and formability were further increased by the method of using Ar+He mixed gas as a shield gas as compared with Ar gas. Formabilities of joints were recorded ranging from $58\%\;to\;70\%$ of that of base metal with different shield gases.

• Journal of Welding and Joining
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• 제33권2호
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• pp.69-77
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• 2015

High strength steels have been continually being developed to improve in fuel economy in automotive and ensure safety of passengers. New bonding and welding methods have been required for improving weldability on high strength steels. In this study, resistance spot welding and Weld-bond with nugget diameters of 4.0mm, 5.0mm, 6.0mm and 7.0mm were produced and tested, respectively. In order to confirm the effect of nugget diameters on tensile shear characteristic of the Weld-bond, tensile shear characteristics of Weld-bond were compared with those of resistance spot welding and adhesive bonding. Peak load of Weld-bond were increased as the nugget diameter increases. After appearing maximum peak load continuous fracture followed with second peak owing to load being carried by resistance spot weldment. Fracture modes of the adhesive layer in Weld-bond fractures were represented by mixed fracture mode, which are cohesive failure on adhesive part and button failure at resistance spot welds. The results showed that the tensile shear properties can be improved by applying Weld-bond on TRIP steel, and more apparent with nugget diameter higher than 5${\surd}$t.

• Journal of Welding and Joining
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• 제32권2호
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• pp.29-36
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• 2014

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the ${\delta}$-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at $625^{\circ}C$, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

• 한국자동차공학회논문집
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• 제24권6호
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• pp.709-715
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• 2016

This paper presents a comparison of an experimental study on spot and plug welding of an automotive body panel. Spot welding is a common joining technology used in automotive body panel assembly. In automotive body repair, however, plug welding is widely used due to its technical simplicity and cost benefit. Some researchers have focused on the use of spot welding in the manufacturing process, but there has been very little research done with respect to the engineering analysis of the plug welding process. In this study, two kinds of specimens are considered to compare the difference of failure strength between spot weld and plug weld: normal tension and shear tension. The experimental results show, in both normal tension and shear tension, that spot welding has higher failure strength than plug welding. In addition, plug welding is more vulnerable to shear tension than normal tension. This study can be applied to further studies on practical optimization for maintenance and repair of automotive body panels.

• 대한기계학회논문집
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• 제7권3호
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• pp.263-269
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• 1983

Underwater welding by a gravity arc welding process was investigated by using six types of coated electrodes and SM41A steel plates of 10 mm thickness as base metal and it was ascertained that this process may be put to practical use. Main results obtained are summarized as follows: 1. Angle of electrode affects no influence on bead appearance and the proper range of welding current and diameter of electrode for the high titanium oxide type is relatively wider than that for the ilmenite type. And the lime titania type, high titanium oxide type and ilmenite type of domestic coated arc welding electrodes of .phi.4 mm could attain the soundest underwater welded joints which contain no welding imperfection. 2. According to macro-structure, micro-structure and hardness distribution inspectionson underwater welded joint, the area between the HAZ and the surface of the weld in neighbourhood of the bond has the maximum hardness value. The structure of these parts is martensite and bainite. Other parts contain mocro-ferrite, micro-pearlite structure, which contain soundness of welded joint free from weld imperfection. 3. On consideration of both tensile strength of more than 100% joint efficiency and sufficient impact value, the welding condition which can get optimal welding strength is heat input of 1,400-1,500 J/mm, current of 200-215 ampere (voltage of 32-33 volts) in the case of lime titania type electrode. 4. Underwater welding strength (tensile strength, impact strength) depends on heat input (or current) quantitatively and they have the relationship of parabolic function. Each experimental equation has a high reliability and its percent of mean error is 4.14%. 5. It is suggested that the optimal design of weld strength by welding condition (current, heat input) could be utilized for a quality control of underwater welding.

• 한국강구조학회 논문집
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• 제14권5호통권60호
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• pp.647-656
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• 2002

강교량에서 사용강재의 고강도화에 의한 구조의 경량화, 합리화는 강교량의 제작 및 가설측면에서 강교량의 경제성을 부각시키고 있다. 이러한 추세에 따라서 향후 강교량 건설에 있어서 고강도강재의 적용사례는 지속적으로 증가할 전망이다. 따라서, 교량부재에 고강도강재를 적용하기 위해서는 강재의 제작작업에서 발생하는 다양한 요인, 예를 들면 용접에 의한 용접열, 부재의 절단 및 가공에 의한 변형경화 등과 같은 강재의 용접성 및 용접이음성능을 정확하게 평가하는 것이 매우 중요하다. 따라서, 본 연구에서는 현재 국내에서 생산되고 있는 SM570, POSTEN60, POSTEN80의 조질 고강도강재를 대상으로 고강도강재의 용접에 따른 용접성 및 가공성을 조사하기 위해서 용접방법별로 최고경도시험 및 경사y형용접터짐시험을 실시하였으며, 또한, 용접이음부의 인장강도, 굽힘성, 흡수에너지 및 경도를 조사하기 위해서 일련의 용접이음시험을 실시하였다.

• Journal of Welding and Joining
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• 제27권4호
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• pp.49-53
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• 2009

For Al 6k21-T4 alloy, linear laser welding produced the lower shear-tensile strength than the base metal. This study improved the shear-tensile strength by using the weaving laser at the optimized welding condition, i.e., 2mm weaving width and 25Hz frequency. The large weaving width increased the weld width, therefore improving the joint strength. For the specimen of low strength, the porosity was distributed continuously along the intersection between the plates and fusion line. However, for the optimized welding condition, large oval-shaped porosities were located only in the advancing track of the concave part. Regardless of the welding condition, solidification cracking was initiated at the intersection and propagated through small porosities in the weld part. furthermore, the concave part had more significant porosity in the weld and HAZ, respectively than the convex part. The continuity of porosities played a key role to determine the strength. And, the weaving width was an important parameter to control the strength.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.29-36
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• 2007

The present study examined the mechanical properties of the friction welding of Ni-Cr-Mo to SM45C. Friction welding was conducted at welding conditions of 2,000 rpm, friction pressure of 100MPa, friction time of 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0 seconds, upset pressure of 150MPa, and upset time of 3.0 seconds. When the friction time was 1.6 seconds, the maximum tensile strength of the friction weld happened to be 1,020MPa, which is 120% of the base material's tensile strength(850MPa). At the same condition, the maximum shear strength was 438MPa, which is equivalent to 103% of the base material's shear strength(425MPa). At the same condition, the maximum vickers hardness was Hv490 at Ni-Cr-Mo nearby weld interface, which is higher Hv40 than condition of the friction time 0.8 seconds, and the maximum vickers hardness was Hv305 from weld interface of SM45C, which is higher Hv12 than condition of the friction time 0.8 seconds. The results of microstructure analysis show that the structures of two base materials have fined and rearranged along a column due to heating and axial force during friction, which has affected in raising hardness and tensile strength.