• Structural Engineering and Mechanics
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• 제83권5호
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• pp.693-707
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• 2022

Bonded joints have proven their performance against conventional joining processes such as welding, riveting and bolting. The single-lap joint is the most widely used to characterize adhesive joints in tensile-shear loadings. However, the high stress concentrations in the adhesive joint due to the non-linearity of the applied loads generate a bending moment in the joint, resulting in high stresses at the adhesive edges. Geometric optimization of the bonded joint to reduce this high stress concentration prompted various researchers to perform geometric modifications of the adhesive and adherends at their free edges. Modifying both edges of the adhesive (spew) and the adherends (bevel) has proven to be an effective solution to reduce stresses at both edges and improve stress transfer at the inner part of the adhesive layer. The majority of research aimed at improving the geometry of the plate and adhesive edges has not considered the effect of temperature and water absorption in evaluating the strength of the joint. The objective of this work is to analyze, by the finite element method, the stress distribution in an adhesive joint between two 2024-T3 aluminum plates. The effects of the adhesive fillet and adherend bevel on the bonded joint stresses were taken into account. On the other hand, degradation of the mechanical properties of the adhesive following its exposure to moisture and temperature was found. The results clearly showed that the modification of the edges of the adhesive and of the bonding agent have an important role in the durability of the bond. Although the modification of the adhesive and bonding edges significantly improves the joint strength, the simultaneous exposure of the joint to temperature and moisture generates high stress concentrations in the adhesive joint that, in most cases, can easily reach the failure point of the material even at low applied stresses.

• Journal of Welding and Joining
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• 제32권5호
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• pp.50-57
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• 2014

Friction Stir Welding (FSW) is a complex process with several mutually interdependent parameters. A slight difference from known settings may lead to imperfections in the stirred zone. These inhomogeneities affect on the mechanical properties of the FSWed joints. In order to prevent the failure of the welded joint it is necessary to detect the most critical defects non-destructive. Especially critical defects are wormhole and lack of penetration (LOP), because of the difficulty of detection. Online thermography is used process-accompanying for defect detecting. A thermographic camera with a fixed position relating to the welding tool measures the heating-up and the cool down of the welding process. Lap joints with sound weld seam surfaces are manufactured and monitored. Different methods of evaluation of heat distribution and intensity profiles are introduced. It can be demonstrated, that it is possible to detect wormhole and lack of penetration as well as surface defects by analyzing the welding and the cooling process of friction stir welding by passive online thermography measurement. Effects of these defects on mechanical properties are shown by tensile testing.

• 한국레이저가공학회지
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• 제16권3호
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• pp.11-21
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• 2013

As parts are becoming more complex and smaller with the development of new materials, high-quality laser precision processing is getting the limelight. Laser enables quick processing and less deformation of materials. It also enables welding with diverse materials. In this study, the pole rod and tap for the secondary battery were laser-welded using cross and coaxial nozzles. The results of the comparative analysis of cross and coaxial nozzles according to the processing parameters showed that the coaxial nozzle had more sensitive welding characteristic to the nozzle position or pressure than the cross nozzle. This indicated that the processing parameters should be carefully determined for the welding with the coaxial nozzle. The pole rod and tap were welded together in a form of T joint to improve the output of the secondary battery, and the cross nozzle had a better welding characteristic than the coaxial nozzle.

• Journal of Welding and Joining
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• 제33권4호
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• pp.50-56
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• 2015

In general, discontinuity of metallurgical and structural points of weld zone could decline the fatigue strength. For the lightweight trend, the AHSS application in automotive chassis is in-progress. However, there are few research reports on AHSS welds fatigue strength in especially automotive chassis parts. Therefore, in this study, we evaluated the effects of the factors affecting the AHSS welding fatigue strength. As the result, the stress concentration of weld bead is the most important factor for welding fatigue strength. For the enhancement of welding fatigue strength, we focused on reducing the stress concentration of the welding beads. So, we applied and proved the plasma welding process and GTAW (Gas Tungsten Arc Welding) dressing method. It was verified by uniaxial fatigue specimen, fatigue performance increased from 40 to 60% by applying TIG dressing method compared to the conventional GMAW (Gas Metal Arc Welding). These results could be recommended the enhancement of fatigue performance of AHSS.

• 한국정밀공학회지
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• 제27권3호
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• pp.66-72
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• 2010

Recently, the use of means of transportation of the lightweight aluminum to temper the trend is increasing. More efficient use of lightweight aluminum material to Friction stir welding has been widely attempted. Types of welding tools at the right screw to rotate anti-clockwise direction, when the tensile stress exerted on the location of the top plate to the left in the direction of the welding process to the installation was able to obtain high tensile strength. A5052 to the top of the left in the direction of the welding process to install and, when you installed the right under the A6061 was not easily come up to the top of the A5052. Conversely, at the bottom left to install on top of the A6061 and A5052 have been installed at the bottom of the upper area of the A6061 and A5052 intrude easily form the shape of the hill you can see that it was formed.

• 한국생산제조학회지
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• 제21권2호
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• pp.290-296
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• 2012

Cold-rolled carbon steel sheets are commonly used in railroad car or commercial vehicles such as the automobile. These are mainly fabricated by spot welding which is a kind of electric resistance welding. But fatigue strength of spot welding joint is lower than that of base metal due to high stress concentration at nugget edge of the spot welded part. And fatigue strength of them is especially influenced by not only geometrical and mechanical factors but also welding conditions of the spot welded joint. So for fatigue design of gas welded joints such as TS-type joints, it is necessary to obtain design information on stress distribution at the weldment as well as fatigue strength of spot welded joints. And also, the influence of the geometrical parameters of spot welded joints on stress distribution and fatigue strength must be evaluated. And analysis approach for fatigue test using design of experiment are evaluated optimum factor in TS-type welded joint and geometrical parameters of materials. Using these results, that factors applied to fundamental information for automation of fatigue design.

• 항공우주시스템공학회지
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• 제16권1호
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• pp.12-16
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• 2022

유도 용접은 비접촉식으로 깨끗하고 빠른 공정으로 현재 주목받고 있다. 하지만 열가소성 수지는 전자기장에 영향을 받지 않기 때문에 유도 용접은 서셉터(Susceptor)라는 발열체가 필요하다. 고품질 접합을 목표로 연구가 진행되고 있지만, 결국 발열체라는 이물질이 들어가기 때문에 기준이 필요하다. 시편의 제작과 시험은 ASTM D5868에 근거하여 진행된다. 본 논문에서 평가 기준은 용접된 접합면의 상태와 기공률, 전단강도로 총 3가지를 근거로 판단할 것을 제안한다. 용접되는 접착면은 용융되고 냉각되면서 고형화가 되기 때문에 급격한 온도 변화는 기공을 발생시킬 수 있다. 또한 가열이 균일하지 않다면 원하는 성능을 기대하기 힘들다. PA6 (CF 30%) 엔지니어링 플라스틱을 이용하여 서셉터 제작과 유도 용접 그리고 성능 검증으로 진행하였다.

• Journal of Welding and Joining
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• 제32권6호
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• pp.64-69
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• 2014

The applications by using fiber laser have increased recently. However, due to high beam quality of fiber laser, it is inappropriate to apply the existing laser welding monitoring technology to the fiber laser welding as it is. On this study, thus, we analyzed emission signal with RMS and FFT for the in-process monitoring during fiber laser welding. 12mm-thick 304L stainless steel sheet was used in fiber laser welding and the result showed as follows: The intensity changes in RMS did not clarify the distinction between full penetration and partial penetration. However, as welding speed increases, specific frequency also increases in regards of frequency analysis by using FFT.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.41-41
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• 2009

To evaluate the applicability of dissimilar joining between Mg and Al alloys in automobile manufacturing process, solid state joining processes such as magnetic pulse welding(MPW), friction stir welding(FSW) and friction spot joining(FSJ) were attempted successfully. MPW process has been concentrated mainly on round section tube to tube and tube to bar welds. AZ31 Mg alloy has been successfully welded to pure Al A1070 as well as to Al alloy A3003. While, for friction stir welding of dissimilar sheet joints, AZ31B/A6061 with the thickness of 2mm were used and a square butt joint with a good quality was obtained at the conditions of 0.8mm/sec of travel speed and tool rotation speed of 850rpm. The maximum tensile strength of 179 MPa, which was about 80 % of the Mg base metal tensile strength, has been obtained. Finally, friction spot joining was attempted to make a dissimilar lap joint between AZ31(0.8mm) and A6061(1mm), while the joint exhibited the same level of tensile shear strength as that of similar Mg joint.

• Journal of Welding and Joining
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• 제32권2호
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• pp.43-47
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• 2014

Famous artificial neural network (ANN) is applied to predict proper process window of arc welding. Target weldment is variously combined lap joint fillet welding of automotive steel plates. ANN's system variable such as number of hidden layers, perceptrons and transfer function are carefully selected through case by case test. Input variables are welding condition and steel plate combination, for example, welding machine type, shield gas composition, current, speed and strength, thickness of base material. The number of each input variable referred in welding experiment is counted and provided to make it possible to presume the qualitative precision and limit of prediction. One of experimental process windows is excluded for predictability estimation and the rest are applied for neural network training. As expected from basic ANN theory, experimental condition composed of frequently referred input variables showed relatively more precise prediction while rarely referred set showed poorer result. As conclusion, application of ANN to arc welding process window derivation showed comparatively practical feasibility while it still needs more training for higher precision.