• 한국초전도ㆍ저온공학회논문지
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• 제24권1호
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• pp.8-12
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• 2022

Recently, research on applying composite materials to various industrial fields is being actively conducted. In particular, composite materials fabricated by Fused Deposition Modeling 3D printers have more advantages than existing materials as they have fewer restrictions on manufacturing shape, reduce the time required, weight. With these advantages, it is possible to consider utilizing composite materials in cryogenic environments such as the application of liquid oxygen and liquid hydrogen, which are mainly used in an aerospace and mobility. However, FDM composite materials are not verified in cryogenic environments less than 150K. This study evaluates the characteristics of composite materials such as tensile strength and strain using a UTM (Universal Testing Machine). The specimen is immersed in liquid nitrogen (77 K) to cool down during the test. The specimen is fabricated using 3D print, and can be manufactured by stacking reinforced fibers such as carbon fiber, fiber glass, and aramid fiber (Kevlar) with base material (Onyx). For the experimental method and specimen shape, international standards ASTM D638 and ASTM D3039 for tensile testing of composite materials were referenced.

• Journal of Electrochemical Science and Technology
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• 제15권2호
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• pp.220-241
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• 2024

Due to its unique advantages, electrochemical machining (ECM) is playing an increasingly significant role in the manufacture of difficult-to-machine materials. Most of the current ECM research is conducted at room temperature, with studies on ECM in a cryogenic environment not having been reported to date. This study is focused on the electrochemical dissolution characteristics of typical iron and nickel base alloys in NaNO₃ solution at low temperature (-10℃). The polarization behaviors and passive film properties were studied by various electrochemical test methods. The results indicated that a higher voltage is required for decomposition and more pronounced pitting of their structures occurs in the passive zone in a cryogenic environment. A more in-depth study of the composition and structure of the passive films by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy showed that the passive films of the alloys are modified at low temperature, and their capacitance characteristics are more prominent, which makes corrosion of the alloys more likely to occur uniformly. These modified passive films have a huge impact on the surface morphologies of the alloys, with non-uniform corrosion suppressed and an improvement in their surface finish, indicating that lowering the temperature improves the localization of ECM. Together with the cryogenic impact of electron energy state compression, the accuracy of ECM can be further improved.

• 한국산업융합학회 논문집
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• 제26권2_2호
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• pp.333-340
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• 2023

Environmental regulations are being strengthened worldwide to solve global warming. For this reason, interest in eco-friendly gas fuels such as LNG and hydrogen is continuously increasing. However, when adopting eco-friendly gas fuel, liquefying at a cryogenic temperature is essential to ensure economic feasibility in storage and transportation. Although austenitic stainless steel is typically applied to store cryogenic liquefied gas, structural steel can experience sudden heat shrinkage in the case of leakage in the loading and unloading process of LNG. In severe cases, the phase of the steel may change, so care is required. This study conducted Charpy impact tests on steel material in nine different temperature ranges, from room to cryogenic temperatures, to analyze the effects of cryogenic liquefied gas leaks. As a result of the study, it was not easy to find variations in ductile to brittle transition temperature (DBTT) due to the leakage of cryogenic liquefied gas. Still, the overall impact toughness tended to decrease, and these results were verified through fracture surface analysis. In summary, brittle fracture of the steel plate may occur when a secondary load is applied to steel for hull structural use exposed to a cryogenic environment of -40 ℃ or lower. Therefore, it needs to be considered in the ship design and operating conditions.

• 한국초전도ㆍ저온공학회논문지
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• 제26권1호
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• pp.20-24
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• 2024

Over the past four years, as the COVID-19 pandemic has struck the world, cold chain of COVID-19 vaccination has become a hot topic. In order to overcome the pandemic situation, it is necessary to establish a cold chain that maintains a low-temperature environment below approximately 203K (-70℃), which is the appropriate storage temperature for vaccines, from vaccine suppliers to local hospitals. Usually, cryocoolers are used to maintain low temperatures, but it is difficult for small-scale local distribution to have cryocooler due to budget and power supply issues. Accordingly, in this paper, a cryogenic TSU (Thermal storage unit) system for vaccination cold chain is designed that can maintain low temperatures below -70℃C for a long time without using a cryocooler. The performance of the TSU system according to the energy storage material for using as TSU is experimentally evaluated. In the experiments, four types of cold storage materials were used: 20% DMSO aqueous solution, 30% DMSO aqueous solution, paraffin wax, and tofu. Prior to the experiment, the specific heat of the cold storage materials at low temperature were measured. Through this, the thermal diffusivity of the materials was calculated, and paraffin wax had the lowest value. As a result of the TSU system's low-temperature maintenance test, paraffin wax showed the best low-temperature maintenance performance. And it recorded a low-temperature maintenance time that was about 24% longer than other materials. As a result of analyzing the temperature trend by location within the TSU system, it was observed that heat intrusion from the outside was not well transmitted to the low temperature area due to the low thermal conductivity of paraffin wax. Therefore, in the TSU system for vaccine storage, it was experimentally verified that the lower the thermal diffusivity of the cold storage material, the better low temperature maintenance performance.

• 대한조선학회논문집
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• 제45권5호
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• pp.538-546
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• 2008

In this paper, the constitutive equation is developed to analyze the characteristics of strain-induced plasticity in the range of low temperature of 316 stainless steel. The practical usefulness of the developed equations is evaluated by the comparison between experimental and numerical results. For 316 stainless steel, constitutive equations, which represent the characteristics of nonlinear material behavior under the cryogenic temperature environment, are developed using the Bodner's plasticity model. In order to predict the material behaviour such as damage accumulation, Bodner-Chan's damage model is implemented to the developed constitutive equations. Based on the developed constitutive equations, 3-D finite element analysis program is developed, and verified using experimental results.

• Journal of Advanced Marine Engineering and Technology
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• 제35권6호
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• pp.802-808
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• 2011

극저온 온도 구조 재료의 중요한 기계적 성질 중 하나는 파괴 인성이다. 파괴 인성 시험 방법의 규격화에 대한 연구는 극저온 구조 요소의 개발과 함께 매우 중요한 문제가 되고 있다. 특히 용접부의 경우 극저온 환경 하에서 사용할 때 불안정파괴를 유발할 수 있기 때문에 용접부의 각 미세조직에 따른 기계적 성질 평가가 중요하다. 본 연구에서는 STS-316L 모재와 용접재를 대상으로 액체질소(77K), 액체헬륨(4K), 293K 온도에서 제하컴플라이언스법과 예민화 열처리한 소형화된 시험편 대상으로 파괴인성평가 실험을 수행하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.850-853
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• 2011

우주발사체에 사용하는 극저온 밸브용 위치지시기는 높은 신뢰성과 정확성을 가져야 한다. 극저온 환경에 노출되는 만큼 습기나 외부오염 등 환경 요인에 영향을 받지 않고 밸브의 상태를 측정하여야 한다. 이러한 요구조건을 만족할 수 있도록 영구자석과 리드스위치를 활용한 위치지시기를 개발하였다. 영구자석과 리드스위치의 특성을 분석하고 극저온 환경에 적용할 수 있는 부품을 선정하였다. 그리고 밸브 개폐 정보를 정확하게 측정할 수 있도록 부품의 형상과 위치를 고려하였다. 최종적으로 밸브 시제품에 적용하여 시험을 통해 설계 변수의 타당성을 검증하였다.

• 한국항공우주학회지
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• 제43권11호
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• pp.1028-1034
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• 2015

발사체에 적용되는 솔레노이드 밸브의 경우 산업용 솔레노이드 밸브에 비해 엄격한 전류 및 무게, 크기 제한 조건을 요구한다. 이러한 제한 조건을 만족하며, 솔레노이드 밸브의 작동을 보장하기 위한 추진제탱크 가압제어용 솔레노이드 밸브 설계를 수행하였다. 극저온 상태에서 솔레노이드 전류 상승을 방지하기 위해 구리와 콘스탄탄 재료를 사용한 새로운 형태의 코일 설계를 적용하였으며, 시제품을 이용한 시험결과 측정된 전류는 설계 규격을 만족하고 있다.

• 반도체디스플레이기술학회지
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• 제20권2호
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• pp.19-24
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• 2021

As the size of semiconductor devices decreases, the etching pattern becomes very narrow and a deep high aspect ratio process becomes important. The cryogenic etching process enables high aspect ratio etching by suppressing the chemical reaction of reactive ions on the sidewall while maintaining the process temperature of -100℃. ESC is an important part for temperature control in cryogenic etching equipment. Through the cooling path inside the ESC, liquid nitrogen is used as cooling water to create a cryogenic environment. And since the ESC directly contacts the wafer, it affects the temperature uniformity of the wafer. The temperature uniformity of the wafer is closely related to the yield. In this study, the cooling path was designed and analyzed so that the wafer could have a uniform temperature distribution. The optimal cooling path conditions were obtained through the analysis of the shape of the cooling path and the change in the speed of the coolant. Through this study, by designing ESC with optimal temperature uniformity, it can be expected to maximize wafer yield in mass production and further contribute to miniaturization and high performance of semiconductor devices.

• 한국산업융합학회 논문집
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• 제24권6_2호
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• pp.787-793
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• 2021

The global demand for Liquefied Natural Gas(LNG) continues to increase and is facing a big cycle. To keep pace with the increase in international demand for LNG, the demand for LNG fueled ships is also increasing. Since LNG fuel tanks are operated in a cryogenic environment, insulation technology is very important, and although there are various types of insulation applied to Type C tanks, multi-layer insulation and vacuum insulation are typically applied. Powder insulation materials are widely used for storage and transportation of cryogenic liquids in tanks with such a complex insulation structure. In this study, compression tests at room and cryogenic temperature were performed on closed perlite, glass bubble, and fumed silica, which are representative powder insulation material candidates. Finally, the applicability to the Type C fuel tank was reviewed by analyzing the experimental results of this study.