• Journal of Welding and Joining
• /
• v.35 no.1
• /
• pp.34-42
• /
• 2017

This paper presents a comparative study of the AC and MFDC resistance spot welding process with consideration of sheet thickness. The previous studies have confirmed that there is difference in the optimum welding current and expulsion current with AC and MFDC. The aim of this study was revealing the effect of sheet thickness on weldable current range and expulsion behavior for AC and MFDC welding processes. The optimum welding current of AC was lower (1.6 kA) than MFDC welding process in 0.8 mm sheet thickness. Early nugget growth being caused by the peak current of AC developed weld interface deformation, which resulted in suppressing the growth of corona bond and occurrence of low current expulsion. The resistance spot welding for thicker sheet (1.4 mm) required lower current of 0.6 kA for the expulsion on the MFDC welding process. The growth of contact diameter (size of corona bond) and button diameter was linear up to the expulsion current with MFDC welding process. Therefore, more attention is required when the AC and MFDC resistance spot welding process is applied for different thickness of steel sheet combination for automotive application.

• Korean Journal of Materials Research
• /
• v.10 no.1
• /
• pp.90-96
• /
• 2000

The effects of the type and thickness of underlayers on the crystallographic texture and the sheet resistance of aluminum thin films were studied. Sputtered Ti and Ti/TiN were examined as the underlayer of the aluminum films. The texture and the sheet resistance of the metal thin film stacks were investigated at various thicknesses of Ti or TiN, and the sheet resistance was measured after annealing at $400^{\circ}C$ in an nitrogen ambient. For the Ti underlayer, the minimum thickness to obtain excellent texture of aluminum <111> was 10nm, and the sheet resistance of the metal stack was greatly increased after annealing due to the interdiffusion and reaction of Al and Ti. TiN between Ti and Al could suppress the Al-Ti reaction, while it deteriorated the texture of the aluminum film. For the Ti/TiN underlayer, the minimum Ti thickness to obtain excellent texture of aluminum <111> was 20nm, and the minimum thickness of TiN to function as a diffusion barrier between Ti and Al was 20nm.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.433.1-433.1
• /
• 2014

The research of graphene, a monolayer of carbon atoms with honeycomb lattice structure, has explosively increased after appeared in 2004. As a result, its high transmittance, mobility, thermal conductivity, and outstanding mechanical and chemical stability have been proved. Especially, many researches were executed about the field of transparent electrode highlighting material of substituting the indium tin oxide (ITO). In addition, qualitative and quantitative improvements have been achieved due to many synthesis methods were discovered. Among them, mostly used method is chemical vapour deposition of graphene grown on copper or nickel. The transmittance, mobility, sheet resistance, and other many properties are completely changed according to these two types of synthesis method of graphene. In this research, considering the difference of characteristics as the synthesis method of graphene, what types of graphene should be used and how to use it were studied. The stacked graphene harvested on copper and multi-layer graphene harvested on nickel were compared and analyzed, as a result, the transmittance of 90% and the sheet resistance of $70{\Omega}{\square}$ was showed even though stacked graphene layers were 4 layers. The reason that could bring these results is lowered sheet resistance due to stacked monolayer graphenes. Moreover, light output power of the three stacked graphene spreading layer shows the highest value, but light-emitting diode with multi-layer graphene died out from 12mA due to also its high sheet resistance. Therefore, we need to clarify about what types of graphene and how to use the graphene in use.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.292-292
• /
• 2011

TFT (Thin Film Transistor)에서 공정을 단순화 시키고, 가격을 하락시키기 위해서는 Poly-Si을 대체할 물질이 필요하다. 이 연구에서는 Chalcogenide Material의 하나인 GeTe 박막을 이용하여 TFT Channel으로 사용 가능한 물질인지 알아보기 위하여 Post-Annealing을 한 뒤, 상 변화에 따른 박막의 저항 변화, Carrier Concentration (cm-3)과 Mobility (cm2V-1s-1)의 변화를 알아보았다. Sputtering을 이용하여 증착한 GeTe 100 nm Thin Film 위에 Sputtering을 이용하여 SiO2 5 nm를 Capping Layer로 증착한 후, Post-Annealing을 200$^{\circ}C$, 300$^{\circ}C$, 400$^{\circ}C$, 500$^{\circ}C$로 온도를 변화 시키며 진행하였고, 이로 인하여 GeTe Thin Film에 외부의 영향을 최소화 하였다. 먼저 GeTe Thin Film의 Sheet Resistance를 측정한 결과는 300$^{\circ}C$ 까지 낮은 Sheet Resistance의 거동을 보이며 반면, 400$^{\circ}C$ 이상이 되면 높은 Sheet Resistance의 거동을 보인다. Hall Measurement를 통해, Carrier Concentration과 Mobility를 알아보았다. Carrier Concentration은 온도가 증가하면 1E+19에서 1E+21 까지 증가하며, Mobility는 감소하는 경향을 보인다. 500$^{\circ}C$ Post-Annealed GeTe Thin Film에서는 Resistivity가 상당히 높아 4 Point Probe (Range : 1 mohm/sq~2 Mohm/sq)로 측정이 불가능하다. XRD로 GeTe Thin Film을 분석한 결과 as-grown, 200$^{\circ}C$, 300$^{\circ}C$에서는 Cubic의 결정 구조를 보이며, Sheet Resistance가 급격히 증가한 400$^{\circ}C$, 500$^{\circ}C$에서는 Rhombohedral의 결정구조를 보인다. GeTe Thin Film은 400$^{\circ}C$ 이상의 Post-Annealing 온도에서 cubic 구조에서 Rhombohedral 구조로 상 변화가 일어난다. 위 결과를 통해, 결정 구조의 변화가 GeTe Thin Film의 저항, Carrier Concentration과 Mobility에 밀접한 영향이 미치는 것을 확인하였다.

• Journal of Welding and Joining
• /
• v.31 no.6
• /
• pp.27-31
• /
• 2013

Magnesium alloy is used on parts of aircraft and electronic equipment because of the highest specific strength among the common metal materials. Recently, studies about appling magnesium alloy sheet to automotive bodies are on the increase rapidly. For application to automotive bodies, researches about characteristics of resistance spot welding of magnesium alloy sheet are essential. Magnesium alloy has low boiling point, so getting sound bead shape is difficult when appling varies welding processes. Resistance spot welding is also particular about setting optimum welding conditions because of spatter generation, pores and cracks occurrence in nugget. And life of electrodes is very short because of alloying with copper that main material of electrodes. This requires frequent dressing and replacement of electrodes and decrease in productivity of resistance spot welding on magnesium alloy. Therefore in this study, for effective analysis of changes in tensile shear load and nugget size during electrode life test, evaluate detail characteristics of resistance spot welding on magnesium alloy sheet using dome type electrode.

• Proceedings of the KWS Conference
• /
• 2001.10a
• /
• pp.184-186
• /
• 2001

Quality estimation of the weld has been one of the important issues in RSW which is a main process of the sheet metal fabrication in auto-body industry. It was well known that among the various welding process variables, dynamic resistance has a close relation with nugget formation. In this study, a new quality estimation algorithm is developed with the primary dynamic resistance measured at welding machine timer. For this, Back propagation algorithm of neural network is used.

• Fashion & Textile Research Journal
• /
• v.22 no.3
• /
• pp.386-398
• /
• 2020

This study compared dip-coating and in situ polymerization methods for the development of nanofiber-based E-textile using polypyrrole. Nanofiber webs were fabricated by electrospinning an aqueous poly (vinyl alcohol) (PVA) solution. Subsequently, the PVA nanofiber web underwent thermal treatment to improve water resistance. Dip-coating and in situ polymerization methods were used to deposit polypyrrole on the surfaces of the nanofiber web. An FE-SEM analysis was also conducted to examine specimen surface characteristics along with EDS and FT-IR that analyzed the chemical bonding between polypyrrole and specimens. The line resistance and sheet resistance of the treated specimens were measured. Finally, an electrocardiogram (ECG) was measured with textile sensors made of the polypyrrole-deposited PVA nanofiber webs. The polypyrrole-deposited PVA nanofiber webs fabricated by dip-coating dissolved in the dip-coating solution and indicated damage to the nanofibers. However, in the case of in situ polymerization, polypyrrole nanoparticles were deposited on the surface and inter-web structure of the PVA nanofiber web. The resistance measurements indicated that polypyrrole-deposited PVA nanofiber webs fabricated by in situ polymerization with an average sheet resistance of 5.3 k(Ω/□). Polypyrrole-deposited PVA nanofiber webs fabricated by dip-coating showed an average sheet resistance of 57.3 k(Ω/□). Polypyrrole-deposited PVA nanofibers fabricated by in situ polymerization showed a lower line and sheet resistance; in addition, they detected the electrical activity of the heart during ECG measurements. The electrodes made from polypyrrole-deposited PVA nanofiber webs by in situ polymerization showed the best performance for sensing ECG signals among the evaluated specimens.

• Journal of Welding and Joining
• /
• v.25 no.4
• /
• pp.72-78
• /
• 2007

Aluminized steel sheet is a material with excellent heat resistance, thermal reflection and corrosion resistance. It has wide applications, owing to its low cost and excellent performance, in the petrochemical industry, electric power and other energy conversion systems, etc and has attracted the attention of many investigators. But the welding of aluminized steel sheet has a problem of decreasing tensile-shear strength, caused by mixed Al in the weld. This study investigated behavior of Al and its structural properties to resolve this problem. Several analysis equipment(SEM, EDX, EPMA) were used to investigate Al element in the weld. Also microhardness tester and TEM equipment were used to find the intermetallic compound. As a result of this study, Al-rich zones existed in the weld and Fe-Al intermetallic compounds were found in these zones. At the same time, the weldability of aluminized stainless steel sheet was investigated and compared with that of aluminized steel sheet. Although there is a difference between the base metal of the low carbon steel and stainless steel, it is interpreted that a behavior of Al element in the weld is similar.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.40 no.4
• /
• pp.363-370
• /
• 2020

This paper reports the results of an experimental study using the BOTDR sensor to detect the unbonded location of attached CFRP sheet for structural rehabilitation. A specimens with the unattached CFRP sheet were fabricated for this study, on which BOTDR sensor was attached with a nylon net. During the flexural test of the specimens, the strain of the CFRP sheet was measured using the BOTDR sensor and electric resistance gauges. From the results, it was confirmed that the strain distribution obtained through the BOTDR sensor can be effectively used to visualize and detect the unbonded position of the CFRP sheet. In addition, In addition, the strain measured by the BOTDR sensor was found to be more effective in analyzing the overall structure behavior than the electric resistance strain gauge. The development of a BOTDR sensor with a measuring longth of less than 100 mm will enable accurate detection of the local unbonded position of the CFRP sheet.

• Journal of the Korean institute of surface engineering
• /
• v.22 no.2
• /
• pp.47-54
• /
• 1989

The effects of intermetallic compound growt on the sheet resistance and soldreability as functions of the aging time, the temperature, and the conditions of substrates have been investi-gated in the electroplallic compound (mainy Cu6Sn5and Ni3Sn4) and the number of phase interface increased, the sheet resistance increased. Spread tests showed that the solderability was dereased with the intermetallic compounds growth and increased with the thickness of electroplated Sn. The surface morphology or agin size of the compound layer singificantly affect the solderability. The solderability of Sn/Ni system was superiot to Sn/Ni system was sperior to that of Sn/Cu system and the intermetallic compounds growth was solwer in the former system.