• Proceedings of the KWS Conference
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• 2009.11a
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• pp.45-45
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• 2009

원가 측면에서 유리한 저항점용접(Resistance Spot Welding)이 차체 용접에 80%이상으로 가장 많이 적용되고 있다. 첨단고강도강(Advanced High Strength Steel)의 저항점용접성 및 용접부 특성에 미치는 공정 변수의 영향에 대한 연구결과는 많으나, 합금원소의 영향에 대해서는 전무하다. 특히, Si는 DP(Dual Phase)강에 첨가 시 균일한 마르텐사이트의 분포를 촉진하는 원소로 저항 점용접성 및 용접부 특성에 영향을 미칠 것으로 예상되며, 이에 대한 연구는 보고된바 없다. 본 연구에서는 냉연 DP강의 저항 점용접시 중요한 인자 중 하나인 너깃경과 전단인장강도에 미치는 Si함유량의 영향을 검토하였다. 사용된 강재 및 용접기는 1.2mm 두께의 Si함유량(0, 0.5, 1.0, 1.5wt%)이 다른 인장강도 780~1000MPa급 냉연 DP강과 단상 AC용접기를 사용하였다. 용접조건은 ISO 18278-2규격에 따라 가압력 4kA, 초기가압시간 40cycle, 유지시간 17cycle로 고정하고, 용접전류만 변화하여 용접을 실시하였다. 너깃경은 용접부 단면을 컷팅 후 폴리싱 하여, 광학현미경과 Image Pro plus를 이용하여 측정했으며, 인장시편규격은 JIS Z 3137를 이용하였다. Si함유량이 증가에 따라 스패터 발생 전류는 감소했고, 너깃경은 직선적으로 증가했다. Si함유량 증가에 따른 너깃경 증가 이유는 저항(R) 측정결과, Si함유량 증가에 따라 모재의 저항이 높아져, 따라서 입열량($Q=I^2Rt$)이 많아지기 때문으로 판단되었다. 인정전단강도는 Si함유량 증가에 따라 직선적으로 증가했다. 이러한 이유는 Si함유량 증가에 따라 너깃경이 증가되기 때문으로 판단되었고, 너깃경과 인장전단강도 사이에 직선적 관계(PL(kN)=$3.2N_{dia.}$-0.81, $R^2$=0.93)를 가지고 있었다. 파단양상은 Si함유량에 상관없이 5.4kA이하에서는 계면파단이 일어났고, 6.0kA이상에서는 풀 아웃 파단이 일어났다. 계면파단주원인은 용접부 가장자리에 지름이 약 $5{\mu}m$이하의 예리한 노치가 존재하여 노치응력집중과 HAZ계면 근처에 미접합부가 존재하기 때문으로 판단되었다. 6.0kA이상에서는 예리한 노치가 없었고, HAZ부가 완전히 접합되어 있기 때문에 풀 아웃 파단이 일어난 것으로 판단되었다. 따라서, Si함유량 증가에 따라 적정용접전류 구간은 감소했고, 너깃경은 직선적으로 증가했다. 또한, Si함유량 증가에 따라 인장전간강도는 증가 했으며, 너깃경과 인장전단강도 사이에 직선적 관계를 가지고 있었다. 파단 양상은 Si함유량에 상관없이 5.2kA이하에서는 계면파단이, 6.0kA이상에서는 풀 아웃 파단이 일어났다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.456-464
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• 1997

The effect of the additives on the Zn-Ni alloy electrocrystallization from a chloride bath was investigated by means of electrochemical methodes, scanning electron microscopy and measurement of surface appearance, X-ray diffraction patterns. The additives tested were the surfactant of naphtalene-derivative, saccharin and aliphatic alcohol. The resistance of electrodeposit increased by adding the additives, whereas the effect of additives on resistance was different with current density. The nickel content of alloy deposit was increased by the addition of alcohol, while decreased by the surfactant. The surface roughness, appearance and morphology of deposit were also influenced by the type of additive. The fine, compact grains and good surface roughness could be obtained from the surfactant or alcohol -added bath, and the surfactant or saccharin improved the surface appearance.

• Polymer(Korea)
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• v.27 no.3
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• pp.189-194
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• 2003

Interfacial evaluation, damage sensing and cure monitoring of single carbon fiber/thermo setting composite with different curing processes were investigated using electro-micromechanical test. After curing, the residual stress was monitored by measurement of electrical resistance and then compared to various curing processes. In thermal curing case, matrix tensile strength, modulus and interfacial shear strength were higher than those of ultraviolet curing case. The shrinkage measured during thermal curing occurred significantly by matrix shrinkage and residual stress due to the difference in thermal expansion coefficient. The apparent modulus measured in the thermal curing indicated that mechanical and interfacial properties were highly improved. The reaching time to the same stress of thermal curing was faster than that of UV curing case.

• Proceedings of the Korean Magnestics Society Conference
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• 2006.06a
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• pp.80-81
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• 2006

• Proceedings of the Korean Magnestics Society Conference
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• 1999.04a
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• pp.136-137
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• 1999

• Journal of the Korean Magnetics Society
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• v.7 no.6
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• pp.308-313
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• 1997

The magnetoresistance (MR) and the saturation field behavior of the CoFe-Ag nano granular films as a function of the ferromagnetic underlayer and overlayer materials were investigated. The maximum MR ratio of 25.7 % and the saturation field of 2.1 kOe in the as-deposited 3000 $\AA$ $(Co_{92}Fe_8)_{31}Ag_{69}$ single alloy films at room temperature were obtained. The MR ratio and the saturation field of the 100 $\AA$ alloy film were 1.2 % and 5.2 kOe, respectively. Those of the sandwiched alloy films of 200 $\AA$ thick with the Fe under and overlayer of 100 $\AA$ were 11 % and 1.8 kOe respectively. The reduction of saturation field in the sandwiched alloy films is due to the exchange coupling between the ferromagnetic layers and the alloy layer. Among the Fe and FeNi, the more effective materials to reduce the saturation field of the sandwiched alloy films was Fe.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.399-399
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• 2011

본 논문에서는 Indium tin oxide (ITO) 투명전극의 성장온도($T_G$)가 Cu(In,Ga)$Se_2$ (CIGS) 박막태양전지에 미치는 영향을 살펴 보았다. ITO 박막은 radio-frequency magnetron sputtering을 이용하여 상온에서 $350^{\circ}C$까지의 다양한 $T_G$ 조건에서 i-ZnO/ glass와 i-ZnO/CdS/CIGS/Mo/glass 기판에 증착되었다. ITO의 비저항과 CdS/CIGS 계면 특성은 $T_G$에 크게 영향을 받았다. $T_G{\leq}200^{\circ}C$에서는 $T_G$가 증가할수록 ITO 저항이 감소하였고 이에 따른 series 저항 감소가 태양전지 성능 향상에 기여하였다. 하지만 $T_G$ > $200^{\circ}C$에서는 CdS 버퍼층의 Cd이 CIGS 층으로 확산되어 소자의 p-n 계면이 파괴되는 것을 발견하였다. $T_G=200^{\circ}C$에서 ITO를 증착한 CIGS 태양전지의 경우 가장 높은 광전변환효율을 보였다.

• Journal of the Korean Magnetics Society
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• v.13 no.3
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• pp.91-96
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• 2003

Cross-geometrical Cr/Co/Al-Ox/Co/Ni-Fe tunnel junctions were fabricated by magnetron sputtering. To form an insulating layer, The Al layer was oxidized in an atmosphere of oxygen-argon mixture at low power after deposition. To enhance the coercivity of the bottom Co layer, The Cr seed layer was deposited on the glass and it led to increase in coercivity. The coercivity increase is due to the increase of roughness through the Cr thickness. In over oxidation time, the oxidation of Co bottom layer and flat interface of insulator can increase the bottom Co coercivity. But TMR ratio gradually decrease. TMR ratio is relevant with Cr thickness, insulator thickness, and oxidation time. The maximum TMR ratio was 14% at room temperature and the TMR ratio was decreased to half at 0.51 V.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.87-95
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• 2020

As an experimental study on the corrosion behavior of steel materials to which ATMS method using EIS was applied in concrete, immersion of Ca(OH)₂ saturated aqueous solution and NaCl aqueous solution simulating the environment inside concrete The corrosion behavior was tested. The equivalent circuit was derived through the analysis of the Nyquist plot, and the interfacial resistance and the polarization resistance of the Ca(OH)₂ aqueous solution were compared, and Al ATMS was the best interfacial resistance and Zn ATMS was the best polarization resistance. After burying ATMS steel material of cement mortar, the initial immersion impedance measurement value was the highest in the Zn ATMS test body in the impedance measurement by the immersion time by immersing it in the NaCl aqueous solution. Al ATMS test piece has the highest impedance and is highly reliable. This is because Al, which has a high ionization tendency, is continuously oxidized in a strong alkaline environment to form a film and protect the steel from permeation of chlorine ions.

• Journal of the Korea Institute of Building Construction
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• v.23 no.6
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• pp.727-738
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• 2023

In concrete, the interface between the aggregate and cement paste is often the most critical factor in determining strength, representing the weakest zone. Lightweight aggregate, produced through expansion and firing of raw materials, features numerous surface pores and benefits from low density; however, its overall aggregate strength is compromised. Within concrete, diminished aggregate strength can lead to aggregate fracture. When applying lightweight aggregate to concrete, the interface strength becomes critical due to the potential for aggregate fracture. This study involved coating the surface of the aggregate with blast furnace slag fine powder to enhance the interfacial strength of lightweight aggregate. The impedance of test specimens was measured to analyze interface changes resulting from this surface modification. Experimental results revealed a 4% increase in compressive strength following the coating of the lightweight aggregate surface, accompanied by an increase in resistance values within the impedance measurements corresponding with strength enhancement.