• Structural Engineering and Mechanics
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• 제61권4호
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• pp.475-481
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• 2017

An overhead travelling crane structure of two doubly symmetric welded box beams is designed for minimum cost. The rails are placed over the inner webs of box beams. The following design constraints are considered: local buckling of web and flange plates, fatigue of the butt K weld under rail and fatigue of fillet welds joining the transverse diaphragms to the box beams, fatigue of CFRP (carbon fibre reinforced plastic) laminate, deflection constraint. For the formulation of constraints the relatively new standard for cranes EN 13001-3-1 (2010) is used. To fulfill the deflection constraint CFRP strengthening should be used. The application of CFRP materials in strengthening of steel and concrete structures are widely used in civil engineering applications due to their unique advantages. In our study, we wanted to show how the mechanical properties of traditional materials can be improved by the application of composite materials and how advanced materials and new production technologies can be applied. In the optimization the following cost parts are considered: material, assembly and welding of the steel structure, material and fabrication cost of CFRP strengthening. The optimization is performed by systematic search using a MathCAD program.

• Journal of Welding and Joining
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• 제9권4호
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• pp.50-59
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• 1991

Large steel water pipes in Korea are joined prevalently by bell end method and welded at inside as well as outside of the pipes with the length of leg which is same as or larger than the thickness of pipes. This results in an excessive consumption of material and labor compared with foreign counturies such as USA, so that in our recent situation of requiring a number of water pipes such consumption is very ineffective and an improvement in weld design of water pipes is urgently necessary. In this experimental study, the possibility of reducing the length of leg to 85% of the pipe thickness was investigated through observations of microstructure and cross section of weldments, the tensile test, and the impact test of the field and laboratory specimens. As the results of this study, it was revealed that water pipes which have the leg of fillet about 0.8xthickness show a good weldability, have a greater strength than the base metal and absorb the enough energy to be safe in the working condition of the pipes.

• Journal of Welding and Joining
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• 제25권6호
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• pp.44-52
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• 2007

A welding process of a lifting lug for lifting heavy objects is one of the important welding processes directly related to the safety in shipbuilding. Welding a lifting lug is done in the manually and takes about forty minutes. Working environment for the lifting lug welding is very poor due to an radiant heat and a harmful fume. The purpose of this study is to develop methods of multi-pass welding using the lifting lug welding robot system. This study shows robot welding methods to achieve proper corner, straight and connection welding and an effectiveness of application.

• 대한조선학회논문집
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• 제50권1호
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• pp.41-48
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• 2013

Several fatigue damages have recently been reported which cannot be resolved in the context of the existing fatigue design procedure, and they are suspected to be the cracks induced by the low cycle fatigue mechanism. To tackle the problem, a series of material tests together with fatigue tests have been carried out, and elasto-plastic notch strain analysis using nonlinear kinematic hardening model has been performed. The cyclic stress-strain curves are obtained and the nonlinear kinematic hardening model was calibrated based on the obtained material data. Also, the fatigue test with non-load-carrying cruciform fillet welded joint has been performed in low cycle fatigue regime. Then, the notch strain analyses have been carried out to find the precise elasto-plastic behavior of the material at the notch root of the cruciform joint. The variation of the material property from the base metal via HAZ up to the weld metal was taken into account using spatial variation of the material property. Then the detail elasto-plastic behavior of the welded joint subjected to the repeated cyclic loading has been investigated further through the comparison with the prediction with Neuber's rule. The calibration of the nonlinear kinematic hardening model and nonlinear notch strain analyses have been performed using the commercial FE program ABAQUS.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 추계종합학술대회
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• pp.195-199
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• 2005

현재 조선 산업의 대형 블록제작 용접공정에서 용접용 캐리지(Carriage)를 이용한 반자동 용접 방법이 많이 사용되고 있다. 여기서의 캐리지는 수평 필렛 용접에서 용접 토치를 이송해 주는 장치이지만, 로봇 용접방법처럼 용접선을 추적하는 기능이 없어 곡선용접에는 사용이 불가능하며, 단순히 직선용접에만 사용할 수 있다. 또, 용접선을 추적하는 기능이 없기 때문에 직선용접에서도 용접오류가 자주 발생하여 이를 수정하는데 많은 시간과 비용이 소요되고 있다. 이에 본 논문에서는 현재 사용하고 있는 캐리지에 스트레인 게이지를 이용한 용접선 추적 센서와 80C196KC 마이크로컨트롤러를 추가 설치하여 직선 및 곡선용접에서 용접선을 자동으로 추적할 수 있는 시스템을 개발하여 사선 모형 및 컨테이너 박스 모형 용접선을 제작하여 추적현상에 대해 고찰하여 보았다.

• Journal of Welding and Joining
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• 제30권2호
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• pp.59-64
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• 2012

Welding is an essential process in the automotive industry. Most welding processes that are used for auto body are spot welding and $CO_2$ welding are used in a small part. In production field, $CO_2$ welding process is decreased and spot welding process is increased due to welding quality is poor and defects are occurred in $CO_2$ welding process frequently. But $CO_2$ welding process should be used at robot interference parts and closed parts where spot welding couldn't. Because of the 0.65mm ~ 2.0mm thickness steel sheet were used in the automotive industry, poor quality of welding area such as burn through and under fill were happened frequently in $CO_2$ process. In this paper, we will study about the penetration depth which gives a huge impact on burn through changing a degree of base metal, welding position and torch angle. Voltage, current and welding speed were fixed but degree of base metal, welding position and torch angle were changed. And Cold- Rolled(CR) steel sheet was used. Penetration depth was analysed by multiple regression analysis to derive approximate calculations. And reliability of approximate calculations were confirmed through additional experiments. As the results of this research, we confirmed the effect of torch and plate angle to bead shape. And we present a possibility that can simulate more accurate to weld geometry, as deduced the verification equations that has tolerance of less than 21.69%.