• Journal of the Korea Concrete Institute
• /
• v.19 no.4
• /
• pp.483-490
• /
• 2007

Traditional external post-tensioning method using either steel bars or tendons is commonly used as a retrofitting method for concrete bridges. However, the external post-tensioning method has some disadvantages such as stress concentration at anchorages and inefficient load carrying capability regarding live loads. Thermal prestressing method is a newly proposed method for strengthening and rehabilitation of concrete girder bridges. Founded on a simple concept of thermal expansion and contraction of steel, the method is a hybrid method of external post-tensioning and steel plate bonding, combining the merits of two methods. In this paper, basic concepts of the method are presented and an illustrative experiment is introduced. From actual experimental data, the thermal prestressing effect is substantiated and the FEM approach for its analysis is verified.

• Proceedings of the KWS Conference
• /
• 2010.05a
• /
• pp.74-74
• /
• 2010

모바일 정보통신기기를 중심으로 전자패키지의 초소형화, 고집적화를 위해 플립칩 공법의 적용이 증가되고 있는 추세이다. 플립칩 패키징 접합소재로는 솔더, ICA(Isotropic Conductive Adhesive), ACA(Anisotropic Conductive Adhesive), NCA(Non Conductive Adhesive) 등과 같은 다양한 접합소재가 사용되고 있다. 최근에는 언더필을 사용하는 플립칩 공법보다 미세피치 대응성을 위해 NCP를 이용한 플립칩 공법에 대한 요구가 증가되고 있는데, NCP의 상용화를 위해서는 공정성과 함께 신뢰성 확보가 필요하다. 본 연구에서는 LDI(LCD drive IC) 모듈을 위한 COF(Chip-on-Film) 플립칩 패키징용 NCP 포뮬레이션을 개발하고 이를 적용한 COF 패키지의 신뢰성을 조사하였다. 테스트베드는 면적 $1.2{\times}0.9mm$, 두께 $470{\mu}m$, 접속피치 $25{\mu}m$의 Au범프가 형성된 플리칩 실리콘다이와 접속패드가 Sn으로 finish된 폴리이미드 재질의 flexible 기판을 사용하였다. NCP는 에폭시 레진과 산무수물계 경화제, 이미다졸계 촉매제를 사용하여 다양하게 포뮬레이션을 하였다. DSC(Differential Scanning Calorimeter), TGA(Thermogravimetric Analysis), DEA(Dielectric Analysis) 등의 열분석장비를 이용하여 NCP의 물성과 경화거동을 확인하였으며, 본딩 후에는 보이드를 평가하고 Peel 강도를 측정하였다. 최적의 공정으로 제작된 COF 패키지에 대한 HTS (High Temperature Stress), TC (Thermal Cycling), PCT (Pressure Cooker Test)등의 신뢰성 시험을 수행한 결과 양산 적용 가능 수준의 신뢰성을 갖는 것을 확인할 수 있었다.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.57-57
• /
• 2009

산업의 고도화에 따른 구조물의 사용 환경이 열악해지고 최근 에너지저감과 환경문제 개선을 위한 경화의 요구에 따라 뛰어난 내식성 및 우수한 고비강도 특성을 갖고 있는 타이타늄 및 타이타늄합금의 활용에 대한 연구가 많은 주목을 받고 있다. 이에 따라 타이타늄 신합금의 개발뿐만 아니라 기존에 개발되어 비교적 보편적으로 적용되고 있는 타이타늄 부품의 제조 및 성형기술에 대한 수요도 급증하고 있다. 특히, 기기 및 부품 제조를 위한 용접/접합기술도 매우 중요한 요소기술로 자리메김하고 있다. 타이타늄은 산소, 수소 등의 침입형 원소와의 친화력이 강한 활성이 큰 금속으로 용접시 고온에 노출되면 급격히 산화 및 취화 등의 문제를 발생한다. 따라서 타이타늄의 용접시에는 $426^{\circ}C$이상의 온도에서는 대기로부터 용접부가 차단되도록 하는 쉴딩기술이 매우 중요하다. 타이타늄의 용접은 일반적으로 아크용접, 전자빔 용접, 레이저 용접 및 확산접합 등이 적용되고 있으나 용접입열 조정이 용이하고 아크 안정성이 높고 용접부의 기계적 특성이 우수한 GTA 용접이 작업성을 고려하여 가장 많이 적용되고 있다. 본 연구에서는 미국용접학회(AWS)의 타이타늄 용접가이드를 분석 및 소개하였고, 1t 이하의 박판 CP Ti를 대상으로 GTAW 용접부 미세조직 및 기계적 특성을 분석하였다. 이때, 용접 비드폭 제어 및 펄스 용접기술을 통하여 박판 타이타늄의 최적 GTAW 공정변수 제어기술을 분석하였다.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.6
• /
• pp.119-128
• /
• 2008

In this study, new moment-resisting precast concrete beam-column joint is proposed for moderate seismic regions. It has the connection reinforcing bars, penetrated the joint and lap-spliced with the bottom bars of precast U-shaped PC beam. To evaluate the performance for noncontact lapped splice, experimental and analytical works were conducted. Major variables for tests are the length of lap, the diameter of connection reinforcing bars, and the distance between lapped bars. Analytic research was performed nonlinear finite element method. Analytic research focused on crack pattern, load-deflection curve, comparison of internal force, evaluation of ductility strains of reinforcement bar. Results of experimental and analytical works show that the these variables has much influence on flexural strength and ductility, and joint behavior.

• Journal of Welding and Joining
• /
• v.25 no.5
• /
• pp.45-50
• /
• 2007

The Ni-base superalloy GTD111 DS is used in the first stage blade of high power land-based gas turbines. Advanced repair technologies of the blade have been introduced to the gas turbine industry over recent years. The effect of the filler metal powder on Transient Liquid Phase bonding phenomenon and tensile mechanical properties was investigated on the GTD111 DS superalloy. At the filler metal powder N series, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid filler metal powder was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The bond strength of N series filler metal powder was over 1000 MPa. and ${\gamma}'$ phase size of N series TLP bonded region was similar with base metal by influence of Ti, Al elements. At the insert metal powder M series, the Si element fluidity of the filler metal was good but microstructure irregularity on bonded region because of excessive Si element. Nuclear of solids formed not only from the base metal near the bonded interlayer but also from the remained filler metal powder in the bonded interlayer. When the isothermal solidification was finished, the content of the elements in the boned interlayer was approximately equal to that of the base metal. But boride and silicide formed in the base metal near the bonded interlayer. And these boride decreased with the increasing of holding time. The bond strength of M series filler metal powder was about 400 MPa.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.16 no.5
• /
• pp.13-21
• /
• 2012

In this study, the response modification factor for a RC IMRF is evaluated via pushover analysis, where 5-story structures were designed in accordance with KBC2009. The bending moment-curvature relationship for beams and columns was identified with a fiber model, and the bending moment-rotation relationship for beam-column joints was calculated using a simple and unified joint shear behavior model and the moment equilibrium relationship for the joint. The results of the pushover analysis showed that the strength of the structure was overestimated with negligence of the inelastic shear behavior of the beam-column joint, and that the average response modification factor for category C was 7.78 and the factor for category D was 3.64.

• Journal of the Korea Concrete Institute
• /
• v.28 no.3
• /
• pp.365-373
• /
• 2016

Ultra-High-Performance Steel Fiber-Reinforced Concrete (SUPER Concrete) exhibits improved compressive and tensile strengths far superior to those of conventional concrete. These characteristics can significantly reduce the cross sectional area of the member and the anchorage strength of a headed bar is expected to be improved. In this study, the anchorage strengths of headed bars with $4d_b$ or $6d_b$ embedment length were evaluated by simulated exterior beam-column joint tests where the headed bars were used as beam bars and the joints were cast of 120 or 180 MPa SUPER Concrete. In all specimens, the actual yield strengths of the headed bars over 600 MPa were developed. Some headed bars were fractured due to the high anchorage capacity in SUPER Concrete. Therefore, the headed bar with only $4d_b$ embedment length in 120 MPa SUPER Concrete can develop a yield strength of 600 MPa which is the highest design yield strength permitted by the KCI design code. The previous model derived from tests with normal concrete and the current design code underestimate the anchorage capacity of the headed bar anchored in SUPER Concrete. Because the previous model and the current design code do not consider the effects of the high tensile strength of SUPER Concrete. From a regression analysis assuming that the anchorage strength is proportional to $(f_{ck})^{\alpha}$, the model for predicting anchorage strength of headed bars in SUPER Concrete is developed. The average and coefficient of variation of the test-to-prediction values are 1.01 and 5%, respectively.

• Journal of the Korean Wood Science and Technology
• /
• v.41 no.1
• /
• pp.51-57
• /
• 2013

In order to know the shear performances of a bolted connection in reinforced glulam depending upon the combination of textile glass fiber, a tensile-type shear test was conducted. Textile glass fiber was used as a reinforcement, whose glass fiber arrangement was a plain weaving type or a diagonal cloth type. Reinforced glulam was made up of 5 plies and it was produced by inserting and laminating the plies between laminas depending upon a changed insert position and combination form of textile glass fiber. Tensile-type shear test specimens were a steel plate insert-type and joined at end-distance 7D with bolts whose diameter 12 or 16 mm. In textile glass fiber reinforced glulam, whose volume ratio was 1%, the yield shear strength of a 12 mm bolted connection increased by 10% when a test specimen had reinforced internal layers than when external layers were reinforced. As for textile glass fiber reinforced glulam, whose volume ratio was 2%, the yield shear strength of a 12 mm bolted connection increased significantly by about 22% compared to the bolted connection of non-reinforced glulam, and the yield shear strength of a 16 mm bolted connection was improved by about 20% compared to the bolted connection of non-reinforced glulam.

• Journal of the Korean Society of Radiology
• /
• v.8 no.7
• /
• pp.371-376
• /
• 2014

The process of flip-chip bump bonding, Au wire bonding and encapsulation were sucessfully developed and modularized. The CdTe sensor and ROIC were optimally jointed together at $150^{\circ}C$ and $270^{\circ}C$ respectively under24.5 N for 30s. To make SnAg bump on ROIC easy to be bonded, the higher bonding temperature was established than CdTe sensor's. In addition, the bonding pressure was lowered minimally because CdTe Sensor is easier to break than Si Sensor. CdTe multi-energy sensor module observed were no electrical failures in the joints using developed flip chip bump bonding and Au wire bonding process. As a result of measurement, shearing force was $2.45kgf/mm^2$ and, it is enough bonding force against threshold force, $2kgf/mm^2s$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.143-144
• /
• 2010

3-5족 화합물 반도체를 이용한 집광형 삼중 접합 태양전지는 40% 이상의 광변환 효율로 많은 주목을 받고 있다[1]. 삼중 접합 태양전지의 하부 셀은 기계적 강도가 높고 장파장을 흡수할 수 있는 Ge이 사용된다. Ge위에 성장될 III-V족 단결정막으로서 Ge과 격자상수가 일치하는 GaInP나 GaAs가 적합하고, 성장 중 V족 원소의 열확산으로 인해 Ge과 pn접합을 형성하게 된다. 이때 GaInP의 P의 경우 GaAs의 As보다 확산계수가 낮아 태양전지 변환효율향상에 유리한 얇은 접합 형성이 가능하고, 표면 에칭효과가 적기 때문에 GaInP를 단결정막으로 선택하여 p-type Ge기판 위 성장으로 단일접합 Ge구조 제작이 가능하다. 하지만 이종접합 구조 성장으로 인해 발생한 계면사이의 전위나 미세결함들이 결정막내부에 존재하게 되며 이러한 결함들은 광학소자 응용 시 비발광 센터로 작용할 뿐 아니라 소자의 누설전류를 증가시키는 원인으로 작용하여 태양전지 변환효율을 감소시키게 된다. 이에 결함감소를 통해 소자의 전기적 특성을 향상시키고자 수소 열처리나 플라즈마 공정을 통해 수소 원자를 박막내부로 확산시키고, 계면이나 박막 내 결함들과 결합시킴으로서 결함들의 비활성화를 유도하는 연구가 많이 진행되어 왔다 [2][3]. 하지만, 격자불일치를 갖는 GaInP/Ge 구조에 대한 수소 열처리 및 불순물 준위의 거동에 대한 연구는 많이 진행되어 있지 않다. 따라서 본 연구에서는 Ga0.45In0.55P/Ge구조에 수소 열처리 공정을 적용을 통하여 단결정막 내부 및 계면에서의 결함밀도를 제어하고 이를 통해 태양 전지의 변환효율을 향상시키고자 한다. <111> 방향으로 $6^{\circ}C$기울어진 p-type Ge(100) 기판 위에 유기금속화학증착법 (MOCVD)을 통해 Si이 도핑된 200 nm의 n-type GaInP층을 성장하여 Ge과 단일접합 n-p 구조를 제작하였다. 제작된 GaInP/Ge구조를 furnace에서 250도에서 90~150분간 시간변화를 주어 수소열처리 공정을 진행하였다. 저온 photoluminescence를 통해 GaInP층의 광학적 특성 변화를 관찰한 결과, 1.872 eV에서 free-exciton peak과 1.761 eV에서 Si 도펀트 saturation에 의해 발생된 D-A (Donor to Acceptor)천이로 판단되는 peak을 검출할 수 있었다. 수소 열처리 시간이 증가함에 따라 free-exciton peak 세기 증가와 반가폭 감소를 확인하였고, D-A peak이 사라지는 것을 관찰할 수 있었다. 이러한 결과는 수소 열처리에 따른 단결정막 내부의 수소원자들이 얕은 불순물(shallow impurity) 들로 작용하는 도펀트들이나, 깊은 준위결함(deep level defect)으로 작용하는 계면근처의 전위, 미세결함들과의 결합으로 결함 비활성화를 야기해 발광세기와 결정질 향상효과를 보인 것으로 판단된다. 본 발표에서는 상술한 결과를 바탕으로 한 수소 열처리를 통한 박막 및 계면에서의 결함준위의 거동에 대한 광분석 결과가 논의될 것이다.