• 토지주택연구
• /
• 제12권3호
• /
• pp.97-108
• /
• 2021

교대구조물에서는 교대 배면의 성토체 축조로 인한 수평방향응력의 증가로 인한 측방유동문제 및 구조물에 작용하는 온도하중 등의 영향으로 인해 접속슬래브, 거더, 베어링등의 파손이 빈번히 발생되고 있는 실정이다. 이에 대한 대책공법으로 보강토 일체형 교대(GRS (Geosynthetic-Reinforced Soil) integral bridge)가 제안되었다. 보강토 일체형 교대는 GRS 보강토 옹벽과 일체형 교대의 구조형식을 혼합한 형태의 구조물이다. 본 연구에서는 기존 PSC 거더교, 기존 보강토 일체형 교대 및 브라켓형 보강토 일체형 교대(새롭게 개발된 LH형 GRS 보강토 교대)의 시공순서와 지진하중조건을 고려하여 수치해석을 실시하였다. 그 결과 브라켓형 보강토 일체형 교대가 다른 구조물에 비해 응력집중과 교대·뒷채움간 부등침하 영향에 의한 기초지반의 변형에 대해 가장 유리한 것으로 파악되었다. 더 나아가 GRS 보강토 일체형 교대(브라켓형 포함) 구조물은 내진안정성에서도 가장 안정한 것으로 파악되었다.

• Wind and Structures
• /
• 제37권4호
• /
• pp.289-302
• /
• 2023

Insulating glass units (IGUs) have been widely used in buildings in recent years due to their superior thermal insulation performance. However, because of the panel reciprocating motion and fatigue deterioration of sealants under long-term wind loads, many IGUs have the problem of early failure of watertight properties in real usage. This study aimed to propose a statistical method for wind-induced deflection of IGU panels during the whole life service period, for further precise analysis of the accumulated fatigue damage at the sealed part of the edge bond. By the estimation of the wind occurrence regularity based on wind pressure return period, the events of each wind speed interval during the whole life were obtained for the IGUs at 50m height in Beijing, which are in good agreement with the measured data. Also, the wind-induced deflection analysis method of IGUs based on the formula of airspace coefficient was proposed and verified as an improvement of the original stiffness distribution method with the average relative error compared to the test being about 3% or less. Combining the two methods above, the deformation of the outer and inner panes under wind loads during 30 years was precisely calculated, and the deflection and stress state at selected locations were obtained finally. The results show that the compression displacement at the secondary sealant under the maximum wind pressure is close to 0.3mm (strain 2.5%), and the IGUs are in tens of thousands of times the low amplitude tensile-compression cycle and several times to dozens of times the relatively high amplitude tensile-compression cycle environment. The approach proposed in this paper provides a basis for subsequent studies on the durability of IGUs and the wind-resistant behaviors of curtain wall structures.

• 한국강구조학회 논문집
• /
• 제26권4호
• /
• pp.323-334
• /
• 2014

본 연구에서는 표준화재에 노출된 무피복 콘크리트충전강관(CFT)기둥의 내화성능 및 거동 특성을 파악하고자 화재실험 및 수치해석 연구를 수행하였다. 실험변수로는 기둥높이, 하중비, 단면크기를 고려하였고, 이들이 CFT 기둥의 내화성능에 미치는 영향을 알아보고자 단면내 온도변화 및 축변형을 분석하였다. 실험결과 모든 실험체의 강관에서 국부좌굴이 발생, 콘크리트로 하중전이가 일어났고, 이후 콘크리트 압괴로 이어졌다. 이는 CFT 기둥의 전체 휨좌굴과 함께 국부좌굴이 내화설계의 주요 변수로 고려되어야 함을 시사한다. 하중비가 증가할수록 콘크리트저항구간이 줄어들면서 전체적인 내화시간이 감소하였다. 강재한계온도에 근거한 합성부재의 내화성능평가는 실제 하중지지력에 의한 내화시간에 비해 다소 보수적임을 확인하였고, 기존 연구자들의 제안식에 의한 성능예측결과도 실제 내화성능과 비교해볼때 개선의 여지가 있었다. 화재시 CFT 기둥의 내화성능을 예측하기 위하여 유한요소해석을 수행하였고, 실험결과와 비교할 때 신뢰성 있는 예측값을 나타냄을 확인하였다.

• 마이크로전자및패키징학회지
• /
• 제17권3호
• /
• pp.17-26
• /
• 2010

반도체 패키지에 사용되고 있는 유연 솔더는 환경 보호 필요성 대문에 무연 솔더로 빠르게 대체되고 있다. 이와 같은 무연 솔더에 대한 여구는 주로 재료의 발견과 공정 적응성의 관점에서 이루어졌을 뿐, 기계적인 성질이나 신뢰성의 관점에서의 연구는 많이 이루어지지 않았다. 본 논문에서는 무아레 간섭계를 이용하여 유연 솔더와 무연 솔더 실장 WB-PBGA 패키지 결합체의 온도변화에 대한 열-기게적 거동을 해석하였다. 실시간 무아레 간섭계를 이용하여 각 온도 단계에서 변위 분포를 나타내는 간섭무늬를 얻고, 그로부터 유연과 무연의 솔더 조인트를 갖는 WB-PBGA 패키지의 굽힘 변형 거동 및 솔더 볼의 변형률을 비교 분석하였다. 분석결과를 보면 유연 솔더 실장 패키지 결합체의 솔더 볼은 칩경계 부근인 #3 솔더 볼에서 발생하는 전단변형률이 파손에 큰 영향을 미치며, 무연 솔더가 실장된 패키지 결합체의 솔더 볼은 가장 바깥 부근인 #7 솔더 볼에서 발행하는 수직 변형률이 파손에 큰 영향을 미칠 것으로 예측된다, 또한 무연 솔더 실장 패키지 결합체는 같은 온도 조건에서 유연 솔더 실장된 패키지에 비해 굽힘 변형이 휠씬 크게 발생될 뿐 아니라 솔더 볼의 유효변형률도 10% 정도 크게 발생하는 것으로 나타나서 열변형에 의한 파손에 취약할 것으로 예측된다.

• 한국초전도ㆍ저온공학회논문지
• /
• 제25권4호
• /
• pp.19-23
• /
• 2023

The Second-generation high-temperature superconducting (HTS) Rare-Earth Barium Copper Oxide (REBCO) wire is a composite laminate having a multi-layer structure (8 or more layers). HTS wires will undergo multiple loads including the bending-tension loads during winding, high current density, and high magnetic fields. In particular, the wires are subjected to bending stress and magnetic field stress because HTS wires are wound around a circular bobbin when making a high-field magnetic. Each of the different laminated wires inevitably exhibits damage and fracture behavior of wire due to stress deformation, mismatches in thermal, physical, electrical, and magnetic properties. Therefore, when manufacturing high-field magnets and other applications, it is necessary to calculate the stress-strain experienced by high-temperature superconducting wire to present stable operating conditions in the product's use environment. In this study, the finite element model (FEM) was used to simulate the strain-stress characteristics of the HTS wire under high current density and magnetic field, and bending loads. In addition, the result of obtaining the neutral axis of the wire and the simulation result was compared with the theoretical calculation value and reviewed. As a result of the simulation using COMSOL Multiphysics, when a current of 100 A was applied to the wire, the current value showed the difference of 10^-9. The stress received by the wire was 501.9 MPa, which showed a theoretically calculated value of 500 MPa and difference of 0.38% between simulation and theoretical method. In addition, the displacement resulted is 30.0012 ㎛, which is very similar to the theoretically calculated value of 30 ㎛. Later, the amount of bending stress by the circular mandrel was received for each layer and the difference with the theoretically obtained the neutral axis result was compared and reviewed. This result will be used as basic data for manufacturing high-field magnets because it can be expanded and analyzed even in the case of wire with magnetic flux pinning.

• Corrosion Science and Technology
• /
• 제14권2호
• /
• pp.47-53
• /
• 2015

Recently, the bending process is greatly applied to fabricate the pipe line. Bending process can reduce welding joints and then decrease the number of inspection. Thus, the maintenance cost will be reduced. Induction heat bending process is composed of bending deformation by repeated local heat and cooling. By this thermal process, corrosion properties and microstructure can be affected. This work focused on the effect of induction heating bending process on the properties of ASME SA106 Gr. C low carbon steel pipes. Microstructure analysis, hardness measurements, and immersion corrosion test were performed for base metal and bended area including extrados, intrados, crown up, and down parts. Microstructure was analyzed using an optical microscope and SEM. Hardness was measured using a Rockwell B scale. Induction heat bending process has influenced upon the size and distribution of ferrite and pearlite phases which were transformed into finer structure than those of base metal. Even though the fine microstructure, every bent area showed a little lower hardness than that of base metal. It is considered that softening by the bending process may be arisen. Except of I2, intrados area, the others showed a similar corrosion rate to that of base metal. But even relatively high rate of intrados area was very low and acceptable. Therefore, it is judged that induction heat bending process didn't affect boric acid corrosion behaviour of carbon steel.

• 한국강구조학회 논문집
• /
• 제25권1호
• /
• pp.71-80
• /
• 2013

구조, 시공 및 내화측면에서 우수한 콘크리트충전강관(CFT)부재에 대해서 구성재료의 강도가 높은 경우 즉, 콘크리트 압축강도가 100MPa 이상이면서 강관의 항복강도가 650MPa 이상인 경우에 대한 내화성능 평가실험 및 해석적 연구는 미비한 실정이다. 본 연구에서는 이러한 부재에 대해서 내화성능 거동을 파악하고자 ${\Box}-400{\times}400{\times}15$, 부재길이 3,000mm인 실물대 중심재하 내화실험을 행하였다. 실험변수는 중심축력을 5,000kN과 2,500kN로 하였다. 실험결과, 고강도 콘크리트의 폭렬 및 콘크리트 내부 균열에 의하여 축하중이 클수록 조기에 내력을 상실하였다. 또한, 유한차분법과 변형률적합조건을 이용한 비정상온도해석 및 응력해석을 수행하였으며, 고강도 재료모델은 Eurocode모델을 이용하였다. 해석모델은 시간-축변위 관계를 합리적으로 예측할 수 있었다.

• 농업과학연구
• /
• 제43권4호
• /
• pp.656-664
• /
• 2016

Gear reducers are widely used for various agricultural machinery applications such as greenhouses, tractors, and agricultural vehicles. However, thermal deformation and surface pitting at gear tooth flank frequently occur in gear reducers due to high torque. Thus, surface heat treatment of gears is required to improve wear and fatigue resistance. The objective of this study was to simulate the load capacity of the agricultural gear reducer. The simulation was performed for the following three surface heat treatment methods: untreated gears, nitriding heat treatment, and induction hardening method, those mostly used for agricultural gear reducers. The load capacity of the gear reducer was simulated using the safety factor, limit bending stress, and limit contact stress of the gear. The simulation of the load capacity was conducted using KISSsoft commercial software for gear analysis. The main results of simulation test were as follows: first, the nitriding heat treatment resulted in the highest safety factor for bending stress, which was increased about 77% from those of the untreated gears. Second, the induction hardening was the highest safety factor for contact stress, which was increased about 150% from those of the untreated gears. The safety factor for contact stress of the induction hardening was increased about 64% from those of the nitriding heat treatment. The study result suggested that the surface heat treatments could enhance load capacity and that the method of surface heat treatment should be determined based on simulation results for appropriate use scenarios.

• 한국항공우주학회지
• /
• 제36권5호
• /
• pp.472-482
• /
• 2008

본 논문에서는 관측위성의 영상성능을 예측하고 해석하기 위하여 영상 성능의 주요 인자인 전체 시스템의 MTF를 산출하기 위한 시스템 MTF 구조도를 제안하였다. MTF 구조도의 각 요소에 해당하는 기본 모델은 우주 환경에서 광-구조, 열 변형, 자세 및 동역학 특성과 MTF간의 수학적인 관계식으로 표현된다. MTF 기본 모델은 중앙차폐가 있는 광학계의 회절한계, 수차, 비촛점, LOS 지터, 선형운동, 검출기 Integration MTF 등으로 구성된다. 가상의 지구관측위성모델에 대해 영상성능 예측모델링 기법을 적용하여 적절한 결과를 얻을 수 있음을 보였다. 각 기본 모델을 바탕으로 관측위성의 전체 영상성능을 해석하고 개념설계 단계에서 영상성능에 영향을 주는 주요한 설계 매개변수를 도출할 수 있다.

• Journal of Advanced Research in Ocean Engineering
• /
• 제1권2호
• /
• pp.106-114
• /
• 2015

In the fabrication of offshore oil and gas facilities, the significance of dimension control is growing continuously. But, it is difficult to determine the deformation of the structure during fabrication by simple lab tests due to the large size and the complicated shape. Strain-boundary method (a kind of shrinkage method) based on the shell element was proposed to predict the welding distortion of a structure effectively. Modeling of weld geometry in shell element is still a difficult task. In this paper, a concept of imaginary temperature pair is introduced to handle the effect of geometric factors such as groove shape, plate thickness and pass number, etc. Single pass imaginary temperature pair formula is derived from the relation between the groove area and the FE mesh size. By considering the contribution of each weld layer to the whole weldment, multi-pass imaginary temperature is also derived. Since the temperature difference represents the distortion increment, cumulative distortion curve can be drawn by integrating the temperature difference. This curve will be a useful solution when engineers meet some problems occurred in the shipyard. A typical example is shown about utilization of this curve. Several verifications are conducted to examine the validity of the proposed methodology. The applicability of the model is also demonstrated by applying it to the fabrication process of the heavy ship block. It is expected that the imaginary temperature model can effectively solve the modeling problem in shell element. It is also expected that the cumulative distortion curve derived from the imaginary temperature can offer useful qualitative information about angular distortion without FE analysis.