• Elastomers and Composites
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• 제45권4호
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• pp.291-297
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• 2010

차량에서 스트러트 인슐레이터는 도로노면으로부터 발생하는 소음과 진동을 방지하는 역할을 한다. 대부분의 점탄성 마운트들은 고무로 되어있으며 천연고무가 주성분이다. 이러한 고무 부품들은 초기에는 제 역할을 하지만 오랜 시간 고온과 반복하중에 노출되면 성능저하가 일어난다. 고무성능 변화는 NVH를 떨어뜨리고 승차감을 저하시킨다. 본 연구에서는 차량실험을 통해 스프링 변위를 측정하였고, 재현실험에서 가속도 센서를 이용하여 운행거리와 차량연식에 따른 인슐레이터 고무성능을 가속도 값, 고무 영구 변형량, 경도를 나타내었다.

• Advances in concrete construction
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• 제11권4호
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• pp.307-314
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• 2021

Activated hwangtoh (ACT) is a natural resource abundant in South Korea, approximately 15.0% of soil. It is an efficient mineral admixture that has activated pozzolanic properties through high-temperature heating and rapid cooling. The purpose of this study is to improve a curb mixture that can reduce NOx outside and investigate durability performance. To this end, mortar curb specimens were manufactured by replacing OPC with ACT. The ACT substitution ratios of 0.0, 10.0, and 25.0% were considered, and mechanical and durability tests on the curb specimens were conducted at 28 and 91 days of age. Steam curing was carried out for three days for the production of curbs, which was very effective to strength development at early ages. The reduction in strength at early ages could be compensated through this process, and no significant performance degradation was evaluated in the tests on chloride attack, carbonation, and freezing and thawing. The mortar curb with an ACT of 10.0~25.0% replacement ratio exhibited clear NOx reduction through photocatalytic (TiO2) treatment. This is due to the increase in physical absorption through surface absorption and the photocatalyst-containing TiO2 coating. In this study, the reasonable range of the ACT replacement ratio for NOx reduction was quantitatively evaluated through a comprehensive analysis of each test.

• Journal of Ceramic Processing Research
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• 제19권5호
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• pp.388-393
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• 2018

Sublimation of $Bi_2O_3$-based materials is an important degradation issue for the long-term applications of many electronic devices. A series of $SnO_2$-doped $Bi_2O_3$ materials (SBO), was synthesized, densified, and then tested in air or strong reducing atmosphere. The $SnO_2$-doping effects and sublimation kinetics of the SBO materials were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and precise mass loss measurement. The results show that formation of $Bi_2Sn_2O_7$ phase greatly retards the mass loss of SBO. The SBO samples show a surface sublimation in an energy of $52.6kJ{\cdot}mol^{-1}$. However, the sublimation is also controlled by surface microstructure as the amount of vaporizing species (the Bi or gaseous Bi-oxides) is more than 0.1 mass%. The evaporation is retarded on the rough surface and the mechanism of surface evaporation is changed to diffusional control.

• Journal of Ceramic Processing Research
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• 제13권spc2호
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• pp.428-432
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• 2012

Polyamidimide (PAI)-colloidal silica (CS) nanohybrid films were synthesized by an advanced sol-gel process. The synthesized PAI-CS hybrid films have a uniform and stable chemical bonding and there is no interfacial defects observed by TEM. The thermal degradation ratio of PAI-CS (10 wt%) hybrid films is delayed by 100 ℃ compared with pure PAI sample determined by on set temperature range in TGA. The dielectric constant of PAI-CS (10 wt%) hybrid films decreases with increasing CS content up to about 5 wt% but increases at higher CS content, which is not explained simply by effective medium therories (EMT). The duration time of PAI-CS (10 wt%) hybrid coil is 38 sec, which is very longer than that of pure PAI coil sample. The PAI-CS (10 wt%) hybrid film has a higher breakdown voltage resistance than the pure PAI film at surge environment and exhibits superior heat resistance. The PAI-CS (10 wt%) sample shows the advanced and stable thermal emission properties in transformer module compared with the pure PAI sample. This result illustrates that the advanced thermal conductivity and expansion properties of PAI-CS sample in the case of appropriate sol-gel processes brings the stable thermal emission in transformer system. Therefore, new PAI-CS hybrid samples with such stable thermal emission properties are expected to be used as a high functional coating application in ET, IT and electric power products.

• Advances in concrete construction
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• 제15권1호
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• pp.41-46
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• 2023

Sport has no age limit and can be done anywhere and in any condition with minimal equipment. The existence of sports spaces in all parts of the world is considered a citizen's right. One of the activities carried out in this field is installing sports equipment and structures in parks and encouraging citizens to use this equipment for physical health with the least cost and facilities. Installing sports structures in open spaces such as parks is a practical step for developing citizens' sports. Although using devices in parks is acceptable, it is more critical to meet scientific and technical standards. The components of these structures must have high strength and endurance against changes in environmental conditions such as humidity, temperature difference, and corrosion. Among the various causes of material degradation, corrosion has always been one of several fundamental causes of metal equipment failure. Sports structures in open spaces are not safe from corrosion. Uniform corrosion is the most common type of corrosion. This corrosion usually occurs uniformly through a chemical or electrochemical reaction across the surface exposed to the corrosive environment. Rust and corrosion of outdoor sports structures are examples of this corrosion. For this reason, in this research, with the green synthesis of silica nanoparticles and its application in outdoor sports structures, the life span of these structures can be increased for the use of physical exercises as well as their quality.

• 한국공간구조학회논문집
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• 제23권4호
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• pp.81-88
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• 2023

Numerous factors contribute to the deterioration of reinforced concrete structures. Elevated temperatures significantly alter the composition of the concrete ingredients, consequently diminishing the concrete's strength properties. With the escalation of global CO2 levels, the carbonation of concrete structures has emerged as a critical challenge, substantially affecting concrete durability research. Assessing and predicting concrete degradation due to thermal effects and carbonation are crucial yet intricate tasks. To address this, multiple prediction models for concrete carbonation and compressive strength under thermal impact have been developed. This study employs seven machine learning algorithms-specifically, multiple linear regression, decision trees, random forest, support vector machines, k-nearest neighbors, artificial neural networks, and extreme gradient boosting algorithms-to formulate predictive models for concrete carbonation and thermal impact. Two distinct datasets, derived from reported experimental studies, were utilized for training these predictive models. Performance evaluation relied on metrics like root mean square error, mean square error, mean absolute error, and coefficient of determination. The optimization of hyperparameters was achieved through k-fold cross-validation and grid search techniques. The analytical outcomes demonstrate that neural networks and extreme gradient boosting algorithms outshine the remaining five machine learning approaches, showcasing outstanding predictive performance for concrete carbonation and thermal effect modeling.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.343-347
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• 1999

YBCO film을 이용한 meander 형태의 저항형 한류기에서 고장이 발생하였을 때 초기의 과도상태에서 볼수 있는 첨두전류를 억제하기 위하여 shunt 저항을 병렬로 취부한 경우의 전기적특성을 살펴보았다. 인가전압을 16.5 V$_{peak}$로 가하고 R$_0$는 1 ${\omega}$,R$_L$을 7.7 ${\omega}$으로 하고 shunt 저항을 5 ${\omega}$으로 하였을 때 약 12.2 A$_{peak}$의 전류값에서 최초quench가 발생하였으며 초전도 한류소자에 quench 발생으로 인한 저항이 발생함과 동시에 I$_1$으로 흐르던 사고전류의 일부가 shunt 저항이있는 I$_2$으로 서서히 분로하여 첨두전류가 거의 발생하지 않았다. 이때 초전도 한류기를 적용하지 않은 경우 최대 사고전류는 약 16.5 A$_{peak}$이었으며 초전도 한류기를 적용한 경우는 최대 한류전류값이 9 A$_{peak}$에서 4주기후에는 5.8 A$_{peak}$이었다. 인가전압 V$_0$=113 V$_{peak}$이고 표준저항 R$_0$는 1${\omega}$, 그리고 R$_L$을 7.7 ${\omega}$으로 하고 shunt 저항을 5 ${\omega}$으로 하였을 때 사고각 0 $^{\circ}$에서 사고전류값이 최고 23.0 A$_{peak}$까지 상승하고 이후 일정한 값을 유지하였다. 일반적으로 사고발생 직후에는 전류변화율에 의하여 전류값의 급격한 상승을 보이지만 shunt 저항이 전류분류의 역할을 수행하여 첨두전류는 거의 발생하지 않았다. 또한 상온의 gold층의 저항을 감안했을 때 사고발생후 약 36msec 후에 상온에 도달하였으며 shunt 저항이 없는 경우의 11 msec에 비하여 약 3배이상 길어졌다. 사고각 45 $^{\circ}$와 90 $^{\circ}$인 경우는 반복실험에 의한 시편의 특성저하(degradation)에 의하여 정상상태에서 초전도체에 흐르는 전류가 약간 발생하였다. 계통의 신뢰성이 중요한 요소로 작용하는 실제운전에서는 시편의 특성저하에 의한 quench전류의 감소를 감안하여 적절한 운전조건을 도출하여야 한다. 이상에서 앞으로는 장기간의 실제운전 조건을 고려하여 시편의 특성저하(degradation)와 가혹조건에 대한 전기적 특성에 대한 연구를 병행하고자 한다.

• Steel and Composite Structures
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• 제50권3호
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• pp.281-298
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• 2024

Stainless steel bolts (SSB) are increasingly utilized in bolted steel connections due to their good mechanical performance and excellent corrosion resistance. Fire accidents, which commonly occur in engineering scenarios, pose a significant threat to the safety of steel frames. The post-fire behavior of SSB has a significant influence on the structural integrity of steel frames, and neglecting the effect of temperature can lead to serious accidents in engineering. Therefore, it is important to evaluate the performance of SSB at elevated temperatures and their residual strength after a fire incident. To investigate the mechanical behavior of SSB after fire, 114 bolts with grades A4-70 and A4-80, manufactured from 316L austenitic stainless steel, were subjected to elevated temperatures ranging from 20℃ to 1200℃. Two different cooling methods commonly employed in engineering, namely cooling at ambient temperatures (air cooling) and cooling in water (water cooling), were used to cool the bolts. Tensile tests were performed to examine the influence of elevated temperatures and cooling methods on the mechanical behavior of SSB. The results indicate that the temperature does not significantly affect the Young's modulus and the ultimate strength of SSB. Up to 500℃, the yield strength increases with temperature, but this trend reverses when the temperature exceeds 500℃. In contrast, the ultimate strain shows the opposite trend. The strain hardening exponent is not significantly influenced by the temperature until it reaches 500℃. The cooling methods employed have an insignificant impact on the performance of SSB. When compared to high-strength bolts, 316L austenitic SSB demonstrate superior fire resistance. Design models for the post-fire mechanical behavior of 316L austenitic SSB, encompassing parameters such as the elasticity modulus, yield strength, ultimate strength, ultimate strain, and strain hardening exponent, are proposed, and a more precise stress-strain model is recommended to predict the mechanical behavior of 316L austenitic SSB after a fire incident.

• Korean Chemical Engineering Research
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• 제53권5호
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• pp.584-589
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• 2015

잠수함 및 수중무인체계 등의 산소희박환경에서 연료전지를 통한 효과적인 전력생산을 위해서는 높은 수소저장밀도를 갖는 수소공급원이 필요하다. 디젤연료는 액체연료로서 저장 및 공급이 용이하며, 연료전지의 연료가 되는 수소의 단위질량 및 단위부피당 저장밀도가 높은 장점을 갖고 있다. 이러한 디젤연료의 장점을 기반으로 본 연구에서는 산소희박환경에서 수소생산을 위해 디젤연료의 개질반응을 이용하였으며, 산화제로 단위부피당 산소 저장밀도가 높고 액상으로 보관이 용이한 과산화수소 수용액을 기존의 산화제인 물과 산소의 대체산화제로 이용하는 방법을 제안하였다. 과산화수소 수용액의 디젤개질 산화제로써의 특성을 파악하기 위해 물, 공기 산화제와의 비교실험을 진행하였으며, 기존의 산화제와 디젤 개질반응 시 동일한 특성을 갖는 것을 실험적으로 확인하였다. 또한 상용디젤을 연료로 온도 및 과산화수소 수용액의 농도에 따른 개질성능을 평가하였으며, 49시간의 가속 열화실험을 통하여 디젤, 과산화수소 수용액을 이용한 수소생산의 가능성을 확인하였다.

• Applied Biological Chemistry
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• 제33권1호
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• pp.79-86
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• 1990

Bacillus stearothermophilus KFCC 21203를 배양하여 cyclodextrin(CD)을 분해하는 효소를 분리, 정제하고 정제효소의 몇 가지 특성을 조사하였다. 배양액에서 얻은 조효소를 염석, DEAE-cellulose column chromatography, Ultro AcA 34 gel filtration등의 방법으로 15배 정제하였으며 회수율은 77.2%이었다. 정제효소의 specific activity는 12.30units/mg protein 이었고 분자량은 약 29,500정도였다. 이 효소의 작용최적 PH는 5.5, 작용최적온도는 $55^{\circ}C$였으며 $40^{\circ}C$이하의 온도와 pH $5.0{\sim}8.0$의 범위에서 안정하였고 ${\gamma}-CD$에 대한 Km치는 $3.78{\times}10^{-3}$ M이었다. 정제효소는 ${\beta}-CD$에 대한 활성이 매우 낮았고 ${\alpha}-CD$에는 거의 활성이 없었으나 ${\gamma}-CD$에는 매우 높은 활성을 나타내었으며, 이의 분해산물로는 주로 glucose 및 maltose 그리고 소량의 maltotriose였다. 또한 amylose, potato starch, corn starch, amylopectin 및 maltooligomer등에는 높은 활성을, 그리고 glycogen, dextrin에도 비교적 높은 활성을 나타내었고 분해산물로는 주로 glucose와 maltose였다.