• 대한기계학회논문집A
• /
• 제28권11호
• /
• pp.1692-1696
• /
• 2004

This paper presents the thermally induced hot spot characteristics of rubbing surface in the friction pad disk brake. During the braking period, the rubbing surface with irregular asperities that are strongly engaged in rough surface, wear, and deformed surface due to a friction heating may produce an irregular distorted geometry of the disk surface. The tribological interactions between the disk and the pads are unstable if the contact stress is severe, in which the irregularity develops the contact pressure distribution, leading eventually to localized contact, high temperature and formation of hot spots. The computed results of contact spots that are simulated using a coupled thermal-mechanical analysis present sinusoidal distortions and localized extrusions of the disk surface, which are strongly related to a hot spot in the practical disk brake.

• 한국안전학회지
• /
• 제34권5호
• /
• pp.22-30
• /
• 2019

In 2018, overload, overcurrent, insulation aging, and a contact failure caused 659 electric fires. There is almost no failure of electrical socket outlets during their manufacturing or installation period. After several months or several years, overload or overcurrent of electrical socket outlets leads to a contact failure or short circuit which causes an electric fire. Therefore, this paper analyzed for thermal characteristics based on a current value and the change in insulation resistance along with a temperature rise caused by electrical socket outlets and the state of laboratory use in workplaces. As a results, regarding the thermal characteristics based on the current value of each installation year, a temperature increase was related to a current value, an installation year, and whether the contact unit is corroded. Insulation resistance began to decrease when a temperature increased to a certain level. With a lapse of installation year, the temperature at which insulation resistance began to decrease was lowered. This paper can be applicable for the survey data about electrical socket outlet induced fire accidents and management guidelines.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제12권1호
• /
• pp.34-40
• /
• 2012

We have developed a highly sensitive inspection technique based on an electron beam inspection for detecting the contact failure of a poly-Si plugged layer. It was difficult to distinguish the contact failure from normal landing plugs with high impedance. Normally, the thermal annealing method has been used to decrease the impedance of poly-Si plugs and this method increases the difference of charged characteristics and voltage contrast. However, the additional process made the loss of time and broke down the device characteristics. Here, the interval scanning method without thermal annealing was effectively applied to enhance the difference of surface voltage between well-contacted poly-Si plugs and incomplete contact plugs. It is extremely useful to detect the contact failures of non-annealed plug contacts with high impedance.

• 한국항공우주학회지
• /
• 제45권12호
• /
• pp.1021-1030
• /
• 2017

본 논문은 유한요소 열해석 시 불일치하는 격자 접촉면의 열교환계수를 효과적으로 계산하는 방법에 대해 논의한다. 원래 유한요소해석은 두 경계면 사이의 격자가 일치해야 하는데, 복잡하고 다양한 재질의 형상들의 접촉면을 모두 일치하기 위해서는 많은 수고와 계산량이 소요된다. 본문은 이를 극복하기 위해 서로 다른 두 격자면의 접촉 열교환계수를 각 절점으로 효과적으로 분배하는 새로운 기법을 제안하였다. 제시된 기법의 지향점을 서술하고 이를 위해 격자면의 형상에 의존성이 낮은 절점 가중치 분배 기법을 서술하였다. 그리고 이를 3차원의 곡면 접촉면에도 적용하여 제시한 방법론의 범용성을 확인함으로서 열해석을 포함한 여타 유한요소 해석 기법에도 적용 가능함을 알 수 있다.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2010년도 제39회 하계학술대회 초록집
• /
• pp.157-157
• /
• 2010

Vertical-structure light-emitting diodes (V-LEDs) by laser lift-off (LLO) have been exploited for high-efficiency GaN-based LEDs of solid-state lightings. In V-LEDs, emitted light from active regions is reflected-up from reflective ohmic contacts on p-GaN. Therefore, silver (Ag) is very suitable for reflective contacts due to its high reflectance (>95%) and surface plasmon coupling to visible light emissions. In addition, low contact resistivity has been obtained from Ag-based ohmic contacts annealed in oxygen ambient. However, annealing in oxygen ambient causes Ag to be oxidized and/or agglomerated, leading to degradation in both electrical and optical properties. Therefore, preventing Ag from oxidation and/or agglomeration is a key aspect for high-performance V-LEDs. In this work, we demonstrate the enhanced thermal stability of Ag-based Ohmic contact to p-GaN by reducing the thermal compressive stress. The thermal compressive stress due to the large difference in CTE between GaN ($5.6{\times}10^{-6}/^{\circ}C$) and Ag ($18.9{\times}10^{-6}/^{\circ}C$) accelerate the diffusion of Ag atoms, leading to Ag agglomeration. Therefore, by increasing the additional residual tensile stress in Ag film, the thermal compressive stress could be reduced, resulting in the enhancement of Ag agglomeration resistance. We employ the thin Ni layer in Ag film to form Ni/Ag mutli-layer structure, because the lattice constant of NiO ($4.176\;{\AA}$ is larger than that of Ag ($4.086\;{\AA}$). High-resolution symmetric and asymmetric X-ray diffraction was used to measure the in-plane strain of Ag films. Due to the expansion of lattice constant by oxidation of Ni into NiO layer, Ag layer in Ni/Ag multi-layer structure was tensilely strained after annealing. Based on experimental results, it could be concluded that the reduction of thermal compressive stress by additional tensile stress in Ag film plays a critical role to enhance the thermal stability of Ag-based Ohmic contact to p-GaN.

• 융복합기술연구소 논문집
• /
• 제2권1호
• /
• pp.38-42
• /
• 2012

A scroll compressor used in the air conditioning in automobile consists of the fixed scroll and the orbiting scroll. Temperature gradient in the scroll compressor during the operation induces the thermal expansion of two scrolls. Therefore, the gap between scrolls in the initial stage is regarded as an important variable in structural design of the scroll compressor. The coupled thermal-stress analysis was carried out for the scrolls of a scroll compressor. The temperatures of major points of two scrolls in the steady states were referred by the literature of C. Lin. The sequentially coupled thermal-stress analysis is utilized to the heat transfer analysis and the thermal expansion analysis. In the thermal expansion analysis, the contact analysis was considered between the fixed and the orbiting scrolls in order to obtain the penetration distance and the contact pressure between two scrolls. The range of deformation was from 44 to $76{\mu}m$ according to the height of the scroll. The maximum penetration distance of $60{\mu}m$ occurred at the top surface of the fixed scroll in the center of the scroll parts.

• 대한기계학회논문집B
• /
• 제37권3호
• /
• pp.237-242
• /
• 2013

본 논문은 접촉력 보정이 가능한 혈류량 측정기를 제안한다. 기존 혈류량 측정기는 접촉력의 영향을 최소화하기 위해 혈류량 센서를 피부에 고정했으나 이런 점은 전자기기에 적용이 용이하지 않다는 단점이 있다. 이에 본 연구에서는 혈류량 센서에 힘 센서를 집적하여 혈류량과 접촉력의 동시 측정을 통해 접촉력에 따른 혈류량 변화 오차를 보정하여 접촉력에 무관한 혈류량 측정이 가능한 소자 및 방법을 제안한다. 제작된 혈류량 측정기의 성능 분석 결과, 접촉력에 따른 혈류량 변화는 31.7%/N 의 선형적 감소경향임을 확인하였고, 이를 이용하여 접촉력에 따른 혈류량 오차를 보정한 결과, 접촉력 1~3N에서 최대 편차가 9.8%로 나타나 다른 접촉력 조건에서도 일정한 혈류량 측정이 가능함을 보였다. 제안한 소자는 접촉력에 무관하게 정확한 혈류량을 측정할 수 있어, 접촉 가능한 전자기기에의 적용이 용이하다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2010년도 추계학술대회 초록집
• /
• pp.53.2-53.2
• /
• 2010

In this study, we focused on our specialized electrode process for Si back-contact crystalline solar cell. It is different from other well-known back-contact cell process for thermal aspect and specialized process. In general, aluminum makes ohmic contact to the Si wafer and acts as a back surface reflector. And, silver is used for low series resistance metal grid lines. Aluminum was sputtered onto back side of wafer. Next, silver is directly patterned on the wafer by screen printing. The sputtered aluminum was removed by wet etching process after rear silver electrode was formed. In this process, the silver paste must have good printability, electrical property and adhesion strength, before and after the aluminum etching process. Silver paste also needs low temperature firing characteristics to reduce the thermal budget. So it was seriously collected by the products of several company of regarding low temperature firing (below $250^{\circ}C$) and aluminum etching endurance. First of all, silver pastes for etching selectivity were selected to evaluate as low temperature firing condition, electrical properties and adhesive strength. Using the nano- and micron-sized silver paste, so called hybrid type, made low temperature firing. So we could minimize the thermal budget in metallization process. Also the adhesion property greatly depended on the composition of paste, especially added resin and inorganic additives. In this paper, we will show that the metallization process of back-contact solar cell was realized as optimized nano-paste characteristics.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2010년도 춘계학술회의 초록집
• /
• pp.18-20
• /
• 2010

수조구조의 InGaN LED 소자에 적용이 가능하며 높은 열적안정성을 갖는 저저항 고반사율 p형 오믹 전극을 개발하였다. Ag에 Mg을 첨가하여 p형 전극을 이용하여 $400^{\circ}C$, 공기중에서 1분간 열처리 후 $2.2\;{\times}\;10^{-5}\;{\Omega}cm^2$의 낮은 접촉 저항을 얻을 수 있었고, 460 nm 파장에서 82.6%의 높은 반사율을 획득할 수 있었다. 이는 Mg가 첨가됨에 따라 Ag가 고온에서 집괴되는 원인인 산소-공공 결합을 줄여줌으로써 높은 열적 안정성을 얻게 되었다. Ag를 열처리 할 경우, 외부에 존재하는 산소가 공공 자리에 들어간 후, 산소와 공공의 강한 인력에 의해 산소가 침입형 자리에 들어가서면서 두개의 공공과 강하게 bonding을 갖는 diffusion center가 많이 존재하게 된다. 하지만 Mg가 첨가되었을 경우, Oxygen affinity가 강한 Mg에 산소가 먼저 결합을 이루면서 산소-공공결합을 줄여주게 되어 높은 온도에서도 diffusion이 이루어지지 않고 높은 열적 안정성을 갖게 된다.

• 소성∙가공
• /
• 제12권1호
• /
• pp.18-25
• /
• 2003

This paper explains the process design for improving tool life in the conventional hot forging process. The thermal load and the thermal softening are happened by contact between the hotter billet and the cooler tools in hot forging process. Tool life decreases considerably due to the softening of the surface layer of a tool was caused by a high thermal load and long contact time between the tools and the billet. Also, tool life is to a large extent limited by wear, heat crack and plastic deformation in hot forging process. Above all, the main factors which affect die accuracy and tool life we wear and the plastic deformation of a tool. The newly developed techniques for predicting tool life are applied to estimate the production quantity for a spindle component and these techniques can be applied to improve the tool life in hot forging process.