• Journal of Welding and Joining
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• 제26권4호
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• pp.79-84
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• 2008

Use of sheet metal structure is increased in various fields such as automobile, aerospace and communication equipment industry. When this structure is welded, welding distortion is generated due to the non-uniformity of temperature distribution. Recently welding distortion becomes a matter of great importance in the structure manufacture industry because it deteriorates the product's quality by bringing about shape error. Accordingly many studies for solving the problems by controlling the welding distortion are being performed. However, it is difficult to remove all kinds of distortion by welding process, though various kinds of methods for reducing distortion are applied to production. Consequently, straightening process is operated if the high precision quality is requested after welding. The local heating method induces compression plastic deformation by thermal expansion in the heating stage and then leaves constriction of length direction in the cooling stage. Accordingly, in the case of sheet metal structure, straightening effect is expected by heating for the part of distortion. This study includes numerical analysis of straightening effect by the local heating method in distortion comes from production of welded sheet metal structure. Particularly straightening effect followed by dimensions of heating area is analyzed according to the numerical analysis. The numerical analysis is performed by constructing 3-dimensional finite element model for 0.4mm stainless steel-sheet metal. Results of this study confirm that straightening effect changes as heating area increases and the optimum value of heating area that proves the maximum straightening effect exists.

• 한국지반환경공학회 논문집
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• 제18권11호
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• pp.35-40
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• 2017

한랭지역에 건설된 터널은 낮은 기온으로 인하여 콘크리트 라이닝 배면의 동결이 발생하게 되며, 콘크리트 라이닝의 손상을 발생시켜 터널구조물의 내구성을 감소시킨다. 터널 라이닝 배면 지반의 동결을 억제시키기 위하여 터널 라이닝 표면에 발열체를 부착하고 일정시간 동안 발열시켜 콘크리트 라이닝 내부의 온도변화를 측정하였다. 냉동챔버를 제작하여 현장현황을 모사하고 발열체는 탄소나노튜브(CNT, Carbon Nano Tube) 재료를 플레이트로 제작하여 표면에 부착하고 전기공급을 통해 발열시켰다. 발열체를 발열시킴에 따라 콘크리트 라이닝의 내부 위치별 온도변화 분포를 측정하였으며, 외기온도 및 발열온도의 유지시간에 따른 영향을 분석하였다.

• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1837-1848
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• 2004

Interaction behaviors of high-speed compressible viscous flow and thermal-structural response of structure are presented. The compressible viscous laminar flow behavior based on the Navier-Stokes equations is predicted by using an adaptive cell-centered finite-element method. The energy equation and the quasi-static structural equations for aerodynamically heated structures are solved by applying the Galerkin finite-element method. The finite-element formulation and computational procedure are described. The performance of the combined method is evaluated by solving Mach 4 flow past a flat plate and comparing with the solution from the finite different method. To demonstrate their interaction, the high-speed flow, structural heat transfer, and deformation phenomena are studied by applying the present method to Mach 10 flow past a flat plate.

• 마이크로전자및패키징학회지
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• 제31권1호
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• pp.29-34
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• 2024

전류가 전도체를 통과할 때 발생하는 줄 열을 이용한 발열체는 자동차 창유리, 고속열차 창유리 및 태양전지와 같은 다양한 산업 분야에서 수분 제거 등을 위해 널리 연구되고 개발되고 있고, 최근에는 기계적 변형 조건 하에서도 안정적인 가열을 유지할 수 있는 유연 발열체를 개발하기 위하여 여러 나노 구조의 발열체를 이용한 연구가 활발하게 진행중이다. 본 연구에서는 유연성이 우수한 폴리우레탄을 기판으로 선정하고 마그네트론 스퍼터링을 이용하여 낮은 전기비저항(1.6 μΩ-cm)을 가지는 은 (Ag) 박막을 형성하여 발열층으로 이용한 연구를 진행하였다. 2D 박막구조에서의 전면발열에 의하여 열응답속도가 매우 높아 목표 온도의 95%까지 20초 이내에 도달하였으며 우수한 발열재현성을 보여주었다. 또한 기계적 변형이 가해지는 환경에서도 우수한 발열특성이 유지되었으며 반복적인 굽힘 테스트 (10,000회, 곡률반경 5 mm 기준)에서도 3% 이내의 전기저항 증가만이 발생할 정도로 우수한 유연성을 보유하여, 폴리우레탄/은 구조의 면상발열체는 굴곡진 형태를 가진 다양한 기기에서부터 인체분위와 같이 다양한 응력이 가해지는 환경에서 사용할 수 있는 플렉서블/웨어러블 면상발열체로의 적용이 매우 유망하다는 것을 보여준다. 또한 증착된 은 박막 발열 층 구조는 다양한 목적을 위한 기능을 추가하여 다양한 분야에서 사용할 수 있는 플렉서블/웨어러블 발열체로서의 적용 가능성을 보여줍니다.

• Steel and Composite Structures
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• 제9권3호
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• pp.209-221
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• 2009

Heating correction, through heating and flattening a structure with a pressing machine, is the in-situ method used to repair buckled steel structures. The primary purpose of this investigation is to develop an FEM model which can predict the mechanical response of heat-corrected plates accurately. Our model clarifies several unsolved problems. In previous research, the location of the imperfection was limited to the center of the specimen although the mechanical behavior is strongly affected by the location of the imperfection. Our research clarifies the relationship between the location of the imperfection and the mechanical behavior. In addition, we propose further reinforcement methods and validate their effectiveness. Our research concludes that the strength of a buckled specimen can be recovered by heating correction and the use of an adequate stiffener.

• 동력기계공학회지
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• 제9권3호
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• pp.66-70
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• 2005

Structural components for aerospace, electronics and automobile industry are the main applications for magnesium alloys due to their lightweight and high specific strength. The adoption of magnesium alloys in sheet forming processes is still limited, due to their low formability at room temperature caused by the hexagonal crystal structure. In this paper, the authors aim to improve the formability of AZ31 magnesium alloy. For this, experiment and finite element analysis on used warm deep drawing process with a local heating and cooling technique were done. Both die and blank holder were heated at various warm temperature while the punch was kept at room temperature by cooling water.

• Composites Research
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• 제33권6호
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• pp.395-400
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• 2020

본 연구에서는 카본나노튜브(CNT) 면상발열체에 preceramic polymer 중 하나인 실세스퀴아잔을 코팅하여 고온에서 안정적인 발열이 가능한 CNT/SiCN 복합체 시트를 제조하였다. 제조된 복합체 필름은 FE-SEM을 통해 실세스퀴아잔이 CNT 면상발열체의 표면을 모두 코팅한 것을 확인하였다. 또한 800℃의 열처리를 통해 실세 스퀴아잔이 SiCN 세라믹으로 전환되어도 표면의 결함이 발견되지 않고 온전한 구조를 유지하는 것을 확인하였다. CNT/SiCN 복합체 시트는 질소와 공기 분위기 모두에서 기존의 CNT 시트보다도 높은 열적 안정성을 확보할 수 있었다. 마지막으로 제조된 CNT/SiCN 복합체 필름은 대기 중에서 700℃ 이상의 온도로 발열이 가능하였고 발열 후 온도를 식히고 재발열 또한 성공적으로 이루어졌다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.157-159
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• 1996

For the optimal design of the induction heating cooker, precise and accurate analysis of the magnetic field inside the jar must be achieved first. Until now, design methods based on experience has been used in industry field. But this takes a lot of trial and error, high cost and also long development time. So the analysis of the magnetic field distribution is very important. In this paper the magnetic field inside the induction heating cooker is analyzed by using axisymmetrical FEM(finite element method). And the method of the coil location design for the optimal heat source distribution using sensitivity analysis is developed. In addition, the shielding effect of the non-axisymmetrical 3-D ferrite structure used in induction heating cooker is also analyzed by the integral method.

• 한국재료학회지
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• 제25권11호
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• pp.607-611
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• 2015

The microstructural evolution of Grade 91 tempered martensite ferritic steels heat treated at $760{\sim}1000^{\circ}C$ for two hours was investigated using scanning electron microscopy(SEM), energy disperse spectroscopy(EDS), electron backscattered diffraction (EBSD), and transmission electron microscopy(TEM); a microhardness tester was also employed, with a focus on the grain and precipitate evolution process as well as on the main hardening element. It was found that an evolution of tempered martensite to ferrite($760{\sim}850^{\circ}C$), and to fresh martensite($900{\sim}1000^{\circ}C$), occurred with the increase of temperature. Simultaneously, the parabolic evolution characteristics of the low angle grain boundary(LAGB) increased with the increase of the heating temperature(highest fraction of LAGB at $925^{\circ}C$), indicating grain recovery upon intercritical heating. The main precipitate, $M_{23}C_6$, was found to be coarsened slightly at $760{\sim}850^{\circ}C$; it then dissolved at $850{\sim}1000^{\circ}C$. Besides this, $M_3C$ cementite was formed at $900{\sim}1000^{\circ}C$. Finally, the experimental results show that the hardness of the steel depended largely on the matrix structure, rather than on the precipitates, with the fresh martensite showing the highest hardness value.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2454-2465
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• 2023

Film boiling may lead to burnout of the heating element. Even though burnout does not occur, the heating element is subject to deformation because it is not sufficiently strong to withstand external loads. In particular, the ballooning and rupture of a tube under film boiling are important phenomena in the field of nuclear reactor safety. If the tube-type cladding of nuclear fuel ruptures owing to high internal pressure and thermal load, radioactive materials inside the cladding are released to the coolant. Therefore, predicting the ballooning and rupture is important. This study presents numerical simulations to predict the ballooning behavior and rupture time of a horizontal tube at high internal pressure under saturated film boiling. To do so, a multi-step coupled simulation of conjugated film boiling heat transfer and ballooning using creep model is adopted. The numerical methods and models are validated against experimental values. Two different nonuniform heat flux distributions and four different internal pressures are considered. The three-step simulation is enough to obtain a convergent result. However, the single-step simulation also successfully predicts the rupture time. This is because the film boiling heat transfer characteristics are slightly affected by the tube geometry related to creep ballooning.