• Journal of the Korea Concrete Institute
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• v.26 no.3
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• pp.377-384
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• 2014

Recently, the trend toward larger architectural structures continues and accelerates demand for Ultra High Strength Concrete (UHSC) which satisfies structural performance. However, UHSC has weakness in fire and the performance tests are required. In this paper, the change of mechanical properties of 100 MPa grade UHSC exposed to high temperatures ($20^{\circ}C{\sim}800^{\circ}C$) was observed to develop high temperature material model of UHSC: residual compressive strength, modulus of elasticity, property of stress-strain on monotonous loading and property of stress-strain on cyclic loading. In addition, TG/DTA and SEM Images analyses were performed to investigate chemical and physical characteristics of UHSC, and the results of this research were compared with those of previous studies. As a result, UHSC at the heating temperature of $300^{\circ}C$ showed a sharp decrease of residual compressive strength and modulus of elasticity. And It was shown that UHSC had a plastic behavior at more than $400^{\circ}C$ on the cyclic loading and revealed a same tendency in both monotonous and cyclic loading of all heating temperatures. In addition, through TG/DTA and SEM images analyses compared with those from previous studies, it was shown that the deterioration of concrete inner tissue, water evaporation and chemical reaction caused the decrease of residual compressive strength and modulus of elasticity.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.583-592
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• 2008

Recently, the effects of high temperature on compressive strength, elastic modulus and strain at peak stress of high strength concrete were experimentally investigated. The present study is aimed to study the effect of elevated temperatures ranging from 20 to 700 on the material mechanical properties of high strength concrete of 40, 60, 80 MPa grade. In this study, the types of test were the stressed test and stressed residual test that the specimens are subjected to a 25% of ultimate compressive strength at room temperature and sustained during heating and when target temperature is reached, the specimens are loaded to failure. And another specimens are loaded to failure after 24 hour cooling time. Tests were conducted at various temperatures ($20{\sim}700^{\circ}C$) for concretes made with W/B ratios 46%, 32% and 25%. Test results showed that the relative values of compressive strength and elastic modulus decreased with increasing compressive strength grade of specimen and the axial strain at peak stress were influenced by the load before heating. Thermal strain of concrete at high temperature was affected by the preload level as well as the compressive strength. Finally, model equation for compressive strength and elastic modulus of heated high strength concrete proposed by result of this study.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.04a
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• pp.29-30
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• 2013

폴리머 시멘트 모르타르(Polymer-Modified Cement Mortar, 이하, PCM으로 칭함)는 일반 시멘트 모르타르와 비교해서 접착성, 치밀성, 내약품성, 시공성등이 우수한 재료로, 콘크리트 구조물의 보수 보강에 필수불가결한 재료로 인식되고 있다. 그러나, 혼입된 폴리머는 유기물 재료로, 화재와 같은 고온을 받는 경우에는 무기계 재료인 일반 모르타르 및 콘크리트와는 또 다른 고온역에서의 성상을 보일 것으로 예상된다. 이로 인해, PCM으로 보수 보강된 건축물에 화재가 발생할 경우, 고온에서의 안전성 및 화재 후의 보수 보강 필요성에 대한 평가를 행할 필요가 있다. 이에 본 논문에서는 평가시 기본적인 데이터로 활용될 수 있는 PCM의 고온노출시의 역학적 특성에 대한 검토방안으로, 기존의 실험조건 및 실험방법을 응용한 새로운 실험방법을 적용, 비교검토를 행하고, 고온영역에서의 PCM의 역학적 특성에 대해 고찰했다.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.4
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• pp.68-75
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• 2018

This study presents the performance test results and the analyses of the vitiated air heater with high temperature and high pressure. In the performance test, four test conditions and three rake measurement conditions were implemented. In the results of the performance test, the vitiated air heater met targets of temperature and flow rate, and the performance with maximum temperature of 2000 K and maximum combustion pressure of 40 bar was confirmed. Flow rate of provided methane increased 36% more than what was calculated, and 19.6% difference was displayed between measured temperature and theoretically calculated temperature.

• Korean Journal of Food Science and Technology
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• v.23 no.4
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• pp.420-427
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• 1991

The structure of fresh, salted and heated petiole tissue from Chinese cabbage was examined with optical microscope, and the pectin of the tissues was fractionated by successive extraction. The pectin in Chinese cabbage consisted mainly of high methoxyl pectin(pA) and low methoxyl pectin(pB). The pA content was converted to pB markedly by salting and heating at $60{\sim}70^{\circ}C$ for 30 min while heating the cabbage above 80 decreased pB content. The firmness of heated tissue was highly correlated with pB content(r=0.996). Cytorrhysis test showed that pore size of the tissue became smaller by salting and heating at temperature below $80^{\circ}C$.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.235-238
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• 1998

파이프의 양 끝단에 심한 온도구배가 형성될 때 음향이 발생한다는 사실은 이미 알려진 사실이다. 본 연구는 열구동식 열음향냉동기를 구현하기 위해서 1단계로 열원에 의한 음향발생을 달성하고자 했다. 이를 위해 1/4 파장의 열음향 발생장치를 설계 및 제작하여 실험에 사용하였다. 열음향 발생기는 직경 3cm, 길이 16cm의 공명관에 가열부, 박판집적체, 고온부 및 저온부의 열교환기로 구성되며 발생음의 기본주파수는 520Hz로 설계하였다. 고온부를 38$0^{\circ}C$로 가열한 결과 열음향발생기의 개구부로부터 1m 떨어진 곳에서 최초 음압측정값이 약 112dB, 음향출력으로 약 1와트에 해당하는 값을 얻었다. 박판집적체에 급격한 온도구배가 형성되면서 주변의 기체가 자발적인 진동을 하여 형성된 음향동력중 일부는 공명관 벽에 흡수되고 일부는 열교환기에서 점성에 의해 소산된다. 따라서 실제로 음향으로 변하는 부분은 이들을 감한 부분인데 실험결과 약 53%의 음향 생성효율을 달성했으며 이는 스위프트 등이 얻었던 결과보다 우수하다.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.361-362
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• 2009

In this study, measured properties(which is compressive strength, elastic modulus) of concrete by conditions(which is aggregate type, pre-stressed level) using normal aggregate and lightweight aggregate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.153-161
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• 1993

Heat transfer processes in the combustion chamber of a pebble bed regenerative heat exchanger for MHD power generation has been analyzed numerically for heating, evacuation argon heating periods individually. The calculated result well explain the measured temperature change at the top of the pebble bed. The analytical result point out that the length of evacution period and the geometry optimization both for the combustion chamber and the heat storage bed are very important factors for the improvement of thermal performance in MHD power generation.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.59-60
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• 2015

In this study, stress-strain, thermal expansion strain, total strain and high temperature creep strain of ultra-high-strength concrete with compressive strengths of 80, 130, and 180MPa were experimentally evaluated considering elevated temperature and loading condition. Also, transient creep strain has been calculated by using the results of experiment. Experimental coefficient K was proposed with application of non-steady state creep model. It is considered that the experimental results of this study could be baseline data for deformation behavior analysis of ultra-high-strength concrete.

• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.4
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• pp.355-363
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• 2022

Development of supersonic flying vehicle is one of the most latest issue in modern military technology. Specifically, structural integrity of supersonic flying vehicle can be verified by high temperature structural test. High temperature structural test is required to consider thermal load caused by aerodynamic heating while applying structural load simultaneously. Tubular quartz lamps are generally used to generate thermal load by emitting infrared radiation. In this study, modified heat flux model of tubular quartz lamp is proposed based on existing model. Parameters of the proposed model are optimized upon measured heat flux in three dimensions. Finally, thermal load of plate specimen is designed by the heat flux model. In conclusion, it is possible to predict heat flux applied on plate specimen and desired thermal load of high temperature structural test can be obtained.