• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.104-109
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• 2010

Lap joint friction stir welding(LFSW) is an relatively new solid state joining process. A6061-T6 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength to weight ratio and good corrosion resistance. Test methods used in this paper, lock-in thermography, a phase difference between the defect area and the healthy area indicates the qualitative location and size of the defect. In this paper, the defects detected from the thermal image of mechanical properties for weld were evaluated and compared by the lock-in infrared thermography technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.52-60
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• 2018

In the automobile industry, in order to increase the fuel efficiency and conform to the safety regulations, it is necessary to make the vehicles as light as possible. Therefore, it is crucial to manufacture dual phase steels, complex phases steels, MS steels, TRIP steels, and TWIP from high strength steels with a tensile strength of 700Mpa or more. In order to apply ultra-high tensile strength steel to the body, the welding process is essential. Resistance spot welding, which is advantageous in terms of its cost, is used in more than 80% of cases in body welding. It is generally accepted that ultra-high tensile strength steel has poor weldability, because its alloy element content is increased to improve its strength. In the case of the resistance spot welding of ultra-high tensile steel, it has been reported that the proper welding condition area is reduced and interfacial fracture and partial interfacial fracture occur in the weld zone. Therefore, research into the welding quality judgment that can predict the defect and quality in real time is being actively conducted. In this study, the dynamic resistance of the weld was monitored using the secondary circuit process variables detected during resistance spot welding, and the factors necessary for the determination of the welding quality were extracted from the dynamic resistance pattern. The correlations between the extracted factors and the weld quality were analyzed and a regression analysis was carried out using highly correlated pendulums. Based on this research, a regression model that can be applied to the field was proposed.

• Nuclear Engineering and Technology
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• v.38 no.5
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• pp.405-410
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• 2006

Microstructural features and their related mechanical property changes in the 309L cladding and the heat affected zone (HAZ) of SA508 cl.3 steel were investigated through the use of TEM, tensile and small punch (SP) tests. The specimens were irradiated at 563 K up to the neutron fluences of $5.79{\times}10^{19}n/cm^2$ (>1MeV). The microstructure of the clad was mainly composed of a fcc ${\gamma}-phase$, a low percentage of bcc ${\delta}-ferrite$, and a brittle ${\sigma}-phase$. Along the weld fusion line there formed a heavy carbide precipitation with a width of $20{\sim}40{\mu}m$, showing preferential cracking during plastic deformation. The yield stress and ductile-to-brittle transition temperature (DBTT) of the irradiated clads increased. The origin of the hardening and the shift of the DBTT are discussed in terms of the irradiation-produced defect clusters of a fine size and brittle ${\sigma}-phase$.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.666-669
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• 2003

Electrical resistance welded steel pipes showed leakage failure within 5 years usage. Microstructural analysis and hardness test were carried out, whose results gave no evidences about the reason of failure. For the analysis, 3 kinds of ERW pipes with different heat inputs were produced. Microstructural differences according to the different heat inputs were detected. Differences of the amount of inclusion in the weld line were observed. It is concluded that the difference of heat input during ERW pipe production caused the microstructural changes which resulted in the leakage failure.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.329-334
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• 1987

The purpose of this study is to monitor and control the back bead width in arc welding with consumable electrode for reduction of the occurrence of weld defect. The temperature of a point on the weldment surface is selected, as a monitoring parameter, and measured by an optical infra-red sensor. The correlation between the back bead width and the surface temperature is experimentally obtained for various thicknesses of the weldment. The welding travel speed and the surface temperature are taken, respectively, as an input and an output of the welding process under the stable condition of arc. A PI control scheme to maintain the surface temperature at the desired level is proposed by the experimental study.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.533-534
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• 2006

Micro pyramid pattern and its array are designed to enhance the brightness and its uniformity of LGP which is one of key parts in LCD. The designed micro pyramid patterns are fabricated on a Si-wafer first through MEMS process and then a Ni-stamper is electro-plated from the Si pattern master. Adopting the fabricated Ni-stamper, LGPs are injection molded at different mold temperatures and the fidelity of the pattern replication is estimated for each molding conditions and pattern locations. The replicated patterns are found to have some defect such as local short shot or micro weld line which are believed to have negative effect on the performance of the LGP.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.171-173
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• 2005

To evaluate the applicability of dissimilar metal friction stir welding in automobile manufacturing process, friction stir welding trials were carried out for typical 5000 and 6000 series aluminum alloy sheets with 2mm thickness. The sound joints of A15052 and A16061-T6 alloys were successfully formed under a wide range of welding condition. Excellent weld ability has been obtained at a condition of rotating speed 2000rpm and travel speed 100mm/min, while a radiographic test also confirmed defect free joint for this condition. Through the Erichsen cup test, the plastic formability of the FSWelded joints was found to be about 83% of base metal.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.668-673
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• 2004

The Friction Stir Weld (FSW) has been prevailing in the rolling stock manufacturers now a day especially in Europe and Japan, that will be an inevitable welding method in Korean domestic railway industry in the near future. The Welding Institute (TWI) in United Kingdom (UK), who has the right of international patents, invented FSW. To meet the recommendation of Cullen's Report for Ladbroke Grove Rail Inquiry (LGRI) in UK, the FSW is considering for the only alternative welding method to improve the aluminium welding quality, i.e. for improve unzipping defect and crashworthiness on car body in Europe Railways within Railway Safety Research Program.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.5
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• pp.567-574
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• 2007

Aluminum and aluminum alloys have high rate of lightness, recycling property and excellent specific strength. Fields using them have been widening because they ould satisfy both energy reduction and high efficiency in manufactures production. But they have many problems on welding due to high thermal conductivity and reflectivity, so the study to solve these problems ate proceeding actively around the world. This study was purposed to improve weldability and spread application range for aluminium alloys by using the unique property of aluminium which absorb high energy around $800{\mu}m$ wavelength and the higher temperature, the mote absorbtion of laser beam on preheating by multi-wavelength laser beam(pulsed Nd:YAG laser + diode laser with $808{\mu}m$ wavelength). The favorable mechanical properties were acquired by the test results of strength, hardness and leak of weld metal which had reduced its defect like crack and so on.

• Journal of the Korean Society for Railway
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• v.5 no.2
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• pp.55-60
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• 2002

This study proposes the post-processor simulator construction of ultrasonic signal for integrity evaluation of railway truck. For these purposes, the ultrasonic signals for defects(crack) of weld zone in frames are acquired in the type of time series data and echo strength. The detection of the natural defects in railway truck is performed using the characteristics of echodynamic pattern in ultrasonic signal. The constructed post-processor simulator agree fairly well with the measured results of test block(defect location, beam propagation distance, echo strength, etc). Proposed post-processor simulator construction of ultrasonic in this study can be used for the integrity evaluation of railway truck.