• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년 추계학술발표대회 개요집
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• pp.225-227
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• 2006

As rail steel at a crossing area must undergo much higher loading than those at regular railway, Mn-alloyed steel is normally used for its high load-carrying capability and reduced wear rate. However, as these Mn-alloyed steel is tend to have casting defects, manufacturing cost to produce defect-free Mn-alloyed steel becomes quite expensive. Therefore, in order to replace Mn-alloyed steel, we performed build-up welding using CH-90 and investigated regarding to wear characteristics of build-up weld metal.

• 한국재료학회지
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• 제14권4호
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• pp.300-306
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• 2004

A laser welding has been made between sintered tip of Fe-Co-W and low carbon steel shank for the diamond saw blade. The welding characteristics and formation of defect has been investigated carefully for the weld fusion zone in different welding condition. Full penetration has been observed for the whole range of heat input investigated in the present work. Bead width and under-fill have been increased with the increase of heat input. With increasing of heat input small cavities were decreased while large cavities were increased. The ratio of total cavity area to the entire weld bead area was not changed significantly with change of heat input. Most of cavities were found near the tip, and supposed to be formed from the pore in the tip.

• 소성∙가공
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• 제9권1호
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• pp.10-16
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• 2000

This research investigates microstructures and fatigue properties of the weldments of 6005A aluminum alloy developed for railroad vehicles. The samples were extruded into a truss structure and welded together using the gas metal arc welding process. The extruded sample showed a wide variation in grain size, possibly due to the frictional heating as well as the inghomogeneous metal flow in the extrusion die. The mechanical properties of the samples were affected by the mirocstructures. The fatigue strength of the welded structure was found to decrease significantly from that of the base metal. It was found that the fatigue characteristics of the welded structure were determined by the microstructure of the parent metal as well as weld defects such as porosities and the liquation cracks.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권4호
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• pp.770-783
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• 2015

Lately, high production rate welding processes for Al alloys, which are used as LNG FPSO cargo containment system material, have been developed to overcome the limit of installation and high rework rates. In particular, plasma-metal inert gas (MIG) hybrid (PMH) welding can be used to obtain a higher deposition rate and lower porosity, while facilitating a cleaning effect by preheating and post heating the wire and the base metal. However, an asymmetric undercut and a black-colored deposit are created on the surface of PMH weld in Al alloys. For controlling the surface defect formation, the wire feeding speed and nozzle diameter in the PMH weld was investigated through arc phenomena with high-speed imaging and metallurgical analysis.

• 한국강구조학회 논문집
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• 제10권3호통권36호
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• pp.423-435
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• 1998

본 연구에서는 기존의 강교에서 흔하게 발견되고 있는 맞대기 용접부의 용입불량으로 인한 부재의 피로강도 저하도를 정량적으로 평가하고자 하였다. 이를 위하여 강교량의 재료로 널리 사용되고 있는 SWS490강으로 제작된 완전용입 및 용입깊이가 서로 다른 불완전용입 맞대기 용접시험편을 대상으로 일정진폭하중시험을 수행하여 S-N선도를 산출하고 이를 비교 검토하였으며, 파괴역학적 방법을 이용하여 불완전용입 용접재의 피로수명을 계산하였다. 본 연구의 결과로서, 완전용입 용접재의 경우 AASHTO의 피로강도등급선도와의 비교에서 피로한도값은 A등급보다 높은 값을 보였고, S-N선도의 기울기는 5.57로 매우 높게 나타났다. 불완전용입 용접재의 경우 불완전용입깊이 D가 증가함에 따라 피로강도가 감소하는데, D=14.7mm인 경우 AASHTO의 E'등급보다 낮게 나타난다. 불완전용입 용접재의 파손거동에서 피로균열은 내부 용접루트 선단부에서 a/c가 매우 작은 반타원형 표면균열의 형태로 발생하고, 시험체의 두께방향으로 진전하여 최종파손을 유발한다. 파괴역학적 방법을 이용한 불완전용입 용접재의 피로수명을 평가하기 위하여 3차원 반타원형 균열형상에 대한 응력확대계수 K를 유한요소해석으로 구하였다. 여기서 얻어진 K값과 실험으로 얻어진 Paris식의 상수를 이용하여 불완전용입 용접재의 피로수명을 계산하여 비교하였다. 그리고 실제 불완전용입 맞대기용접부의 파손으로 붕괴사고가 발생한 성수대교의 수직재에 본 연구결과를 적용하여 피로수명을 계산해 보았다.

• 제어로봇시스템학회논문지
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• 제11권7호
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• pp.595-601
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• 2005

A mobile robot system utilizing NDT (Non-Destructive Testing) method is designed and fabricated f3r automatic integrity evaluation of large sized industrial reservoirs and pipelines. The developed mobile robot can crawl over the outer surface of the industrial facilities even though the shape of the structures is various and unsymmetric. The robot detects defects such as pinholes, cracks and thickness reduction at the wall of the facilities using EMAT (Electro-Magnetic Acoustic Transducer). Image processing technology for weld line detection at the surface of the target and host programs including defect detecting algorithms are also developed. Automation of defect detection for these kinds of large facilities using mobile robots is helpful to prevent significant troubles of the structures without danger of human beings under harmful environment.

• Journal of Mechanical Science and Technology
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• 제15권1호
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• pp.52-60
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• 2001

In this paper, as a new measurement method to estimate the change of material condition, the simplified ultrasonic CT system, which uses the information of three directions, that is, $90^{\circ}$, $+45^{\circ}C$and $-45^{\circ}C$ about inspection plane is proposed. Use of simplified CT system has two merits: Firstly, the measurement time is very short compared with general CT. Secondly, it can detect sensitively small defect in vertical or slant direction about inspection plane because the obtained image is CT image calculated from three directions. From these merits, this method can be considered as an effective method to evaluate material conditions. The basic performance of the proposed method was confirmed through several specimens with several simple defects. In order to confirm the applicability of actual NDT, several kinds of welded specimens are investigated. The result showed that the CT image obtained had good agreement with actual defect of specimens.

• 비파괴검사학회지
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• 제31권6호
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• pp.635-641
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• 2011

In ultrasonic testing of dissimilar metal welds, application of phased array technique in terms of incident beam focusing is not easy because of complicated material structures formed during the multi-pass welding process. Time reversal(TR) techniques can overcome some limitations of phased array since they are self-focusing that does not depend on the geometrical and physical properties of testing components. In this paper, we test the possibility of TR focusing on a defect within anisotropic, heterogeneous austenitic welds. A commercial simulation software is employed for TR focusing and imaging of a side-drilled hole. The performance of time reversed adaptive focal law is compared with those of calculated focal laws for both anisotropic and isotropic welds.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.1940-1944
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• 2004

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.75-78
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• 2001