• Journal of Welding and Joining
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• 제16권4호
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• pp.47-54
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• 1998

Various equipments in plants are welded with two different materials and it is required to investigate the effects of fatigue crack propagation on the neighborhood of a welded portion. The characteristics of fatigue crack growth in the base metal of carbon and stainless steel, in the carbon and stainless steel sides located in the neighborhood of welded portion (carbon/stainless steel), respectively and welded portion, are investigated. The results show that the crack growth in the welded portion (carbon/stainless steel) is an average value of the crack growths in the carbon and stainless steel respectively located in the neighborhood of the welded portion. It is found that the crack growth in the welded portion is not significantly different from those in the carbon and stainless steel sides. Hence it can be concluded that the structure welded with two different materials wold not impede the integrity based on the fatigue crack growth.

• 동력기계공학회지
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• 제6권4호
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• pp.68-72
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• 2002

For the evaluation of a flaw in a welded stainless steel by the Time of Flight Diffraction(TOFD) Method, we have made the reference specimen for experimentation. As a result, we could analyze a specific character and the inner state of the structure in a welded stainless steel and we came to the conclusion as followed. (1) For analyze the structure state of a section in a welded stainless steel through the optical microscope, we could have analyzed the generated shape and the location of a flaw and the inner parts of the structure state through the microscope of eighty magnification and two hundred magnification about the soundness, the heat affected zone(HAZ) and the welded part. (2) Through the comparison with the shape and the size of a flaw in the welded part about the conventional ultrasonic test and the TOFD Method, we could make an observation the special character of the TOFD Method and principles. (3) We analyzed and collected the merit of the TOFD Method on the basis of the experimental result by the shape and the size of a flaw in the inner welded parts. So, we made up a base that we could use as a basic data for a similar flaw like that. Through the study as mentioned above, we could make an observation the flaw detective method and principles used in the TOFD Method.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.20-27
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• 1998

According as the member of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. And, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic evaluation method for them. In this study, by considering nugget edge of the spot weld part of the IB-type spot welded lap joint under tension-shear load to the ligament crack. fatigue strength of various IB-type spot welded lap joints was estimated with the stress intensity factor(S.I.F.) KIII which is fracture mechanical parameter. We could find that fatigue strength evaluation of the IB-type spot welded lap joints by KIII is more effective than the maximum principal stress ($\sigma$1max) at edge of the spot weld obtained from FEM analysis.

• International Journal of Naval Architecture and Ocean Engineering
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• 제2권4호
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• pp.200-210
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• 2010

In this paper, different evaluation methods of Hot Spot Stresses (HSS) have been applied to four different welded structure details in order to compare them and to illustrate their differences. The HSSs at failure-critical locations were calculated by means of a series of finite element analyses. There was good overall agreement between calculated and experimentally determined HSS on the critical locations. While different methods and procedures exist for the computation of the structural hot-spot stress at welded joints, the recommendations within the International Institute of Welding (IIW) guideline concerning the 'Hot Spot Stress' approach were found to give good reference stress approximations for fatigue-loaded welded joints. This paper recommends and suggests an appropriate finite element modeling and hot spot stress evaluation technique based on round-robin stress analyses and experimental results of several welded structure details.

• 오토저널
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• 제13권5호
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• pp.42-50
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• 1991

According as the members and inner and outer plates of the automobile body structure have been thinned their thickness and have become high strength, each part of the body structure has been put more severe stress condition. Therefore, it has been increasingly required to improve the fatigue strength of the spot welded structures. As one of the improving methods for such problem, the author had previously proposed the method of alleviating stress concentration at nugget edge of the spot weld part and improving its fatigue strength [1]. But, because fatigue strength of the spot welded lap joint is influenced by its geometrical and mechanical factors, welding condition and etc., there needs a quantitative and systematic estimation method of them. In this report, by considering nugget edge of the spot weld part of the spot welded lap joint subjected to tensile load to the ligament crack, fatigue strength of various spot welded lap joints was estimated with the stress intensity factor (S.I.F.) K which is fracture mechanical parameter. It is known that evaluation of fatigue strength of the spot welded lap joint by the stress intensity factor (S.I.F.) K is more effective than the maximum stress $(\sigma_{ymax}$) at edge of the spot weld part on the center line of width of the plate.

• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.127-133
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• 2002

Most structures are constantly influenced by repeated weathering phenomena and load action during a period of its utilization, and their component materials become superannuated and their design performance becomes slowly lost. Therefore, it is thought that it is necessary to develop the online monitoring system that can make a great contribution to the maintenance management and disaster prevention of the building structure by sensing any slight change of the entire structure regardless of its inside and outside. Especially, this study was intended to explain the entire system of the online structure by interpreting welded built-up H-beams, of structural steel members having many advantages in terms of the qualities of structural materials, through limit state design, and presenting the basic plan to apply it to the structure.

• 한국철도학회논문집
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• 제5권1호
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• pp.1-9
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• 2002

Where the track is continuously welded over the bridge, the longitudinal forces will be distributed interactively between the track and the sub-structure by the rail-bridge interaction mechanism. The ratio between the longitudinal forces transmitted in each elements depends on the magnitude of the ballast resistance and the stiffness of the sub-structures. In this paper, the main factors affect on the longitudinal rail force are discussed and the parametric study for the behavior of CWR(Continuous Welded Rail) track was executed. It is concluded that the horizontal ballast resistance and the stiffness of the bridge sub-structure are the significant parameters affecting the stability of the continuous welded rail track.

• Structural Engineering and Mechanics
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• 제40권6호
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• pp.801-811
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• 2011

A new experimental technique was developed on the plate-inserted welded tubular joints of spatial grid structures. In the experimental technique, a microcomputer controlling instrument of moire intervention (MCIMI) was adopted. A test was designed on the plate-inserted welded tubular joints of spatial grid structures to show the effectiveness of the MCIMI technique. Both traditional electrical measuring technique and MCIMI technique were employed in the test. The test results showed that the MCIMI technique was feasible in the case of the complicated tests on steel structures. The MCIMI technique not only implemented the limitation of traditional electrical measuring technique, but also improved the accuracy of the test. According to the test results, we further examined the plate-inserted welded tubular joints in the cable-stayed spatial grids of the Binhai International Convention & Exhibition in Tianjin, China. The analysis showed the joints are safely designed with adequate conservatism. The research provided a new application of MCIMI in the field of large-scale structure engineering.

• Nuclear Engineering and Technology
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• 제48권1호
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• pp.259-267
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• 2016

Most manufacturing processes, including welding, create residual stresses. Residual stresses can reduce material strength and cause fractures. For estimating the reliability and aging of a welded structure, residual stresses should be evaluated as precisely as possible. Optical techniques such as holographic interferometry, electronic speckle pattern interferometry (ESPI), Moire interferometry, and shearography are noncontact means of measuring residual stresses. Among optical techniques, ESPI is typically used as a nondestructive measurement technique of in-plane displacement, such as stress and strain, and out-of-plane displacement, such as vibration and bending. In this study, ESPI was used to measure the residual stress on the welded part of butt-welded American Society for Testing and Materials (ASTM) A36 specimens with $CO_2$ welding. Four types of specimens, base metal specimen (BSP), tensile specimen including welded part (TSP), compression specimen including welded part (CSP), and annealed tensile specimen including welded part (ATSP), were tested. BSP was used to obtain the elastic modulus of a base metal. TSP and CSP were used to compare residual stresses under tensile and compressive loading conditions. ATSP was used to confirm the effect of heat treatment. Residual stresses on the welded parts of specimens were obtained from the phase map images obtained by ESPI. The results confirmed that residual stresses of welded parts can be measured by ESPI.

• Journal of Welding and Joining
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• 제28권5호
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• pp.58-63
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• 2010

The purpose of this study is to develop improved boom structures with reliable fatigue strength of weldment and lower production cost. For that purpose, multibody dynamic analysis was performed to evaluate forces acting on arm & boom cylinders and joints of boom structure during operation of an excavator for three working postures, then stress analysis was made to investigate stress distribution around diaphragms at the bottom plate of boom structures which was known to be susceptible to fatigue failures of welded joints, and finally boom structure with optimum arrangement of diaphragms was proposed. This work basically consists of the following two parts: part 1 focuses on multibody dynamic analysis of excavators during operation and part 2 includes evaluations of fatigue strength of welded joints for modified boom structures.