• 대한기계학회논문집A
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• 제26권8호
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• pp.1461-1471
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• 2002

Linear motor has a lot of advantages in comparison with conventional feed mechanisms: high velocity, high acceleration, good positioning accuracy and a long lifetime. An important disadvantage of linear motor is its high power loss and heating up of motor and neighboring machine components in operation. For the application of the linear motors to precision machine tools an effective cooling method and thermal optimizing measures are required. In this paper Finite-Element-Method for the thermal behavior of synchronous linear motor is introduced, which is useful for the design and manufacturing of linear motors. By modeling the linear motor the orthotropic physical properties of the sheet metal and windings were considered and convective coefficient in the water cooler and to the surroundings was defined by analytical and experimental method. The calculated isothermal lines could analyze the heat flow in the linear motor.

• 한국도로학회논문집
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• 제16권6호
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• pp.79-86
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• 2014

PURPOSES : In this study, wasted vinyl aggregate, which possesses better thermal properties than natural aggregate, was used in cement concrete mixture to develop more economical concrete with thermal insulation and freeze prevention effects. METHODS : Slump and air content of the fresh concrete, which substituted its 0%, 5%, and 10% of coarse aggregate with wasted vinyl aggregate, were measured. Compressive strength, Poisson's ratio, elastic modulus, and splitting tensile strength of hardened concrete were measured by laboratory tests. Thermal properties of concrete such as coefficient of thermal expansion, thermal conductivity, and specific heat were also measured according to replacement ratio of wasted vinyl aggregate. Finally, the thermal insulation and freeze prevention effectiveness of the concrete mixed with wasted vinyl aggregate was confirmed through finite element analysis of road pavement crossing above concrete box culvert made from wasted vinyl aggregate. RESULTS : Even though the physical properties of wasted-vinyl-aggregate concrete such as compressive strength, Poisson°Øs ratio, elastic modulus, and splitting tensile strength were inferior to those of ordinary concrete, they met requirements for structural concrete. The thermal properties of concrete were improved by wasted vinyl aggregate because it decreased thermal conductivity and increased specific heat of the concrete. According to the result of finite element analysis, temperature variation in pavement subgrade was mitigated by box culvert made from wasted-vinyl-aggregate concrete. CONCLUSIONS : Through the laboratory test and finite element analysis of this study, it was concluded that the concrete structures made from wasted vinyl aggregate showed thermal insulation and freeze prevention effects.

• 한국염색가공학회지
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• 제16권6호
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• pp.35-43
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• 2004

This study surveys the physical properties of ATY produced with FDY and POY. ATY is made with 70d Nylon FDY and 80d Nylon POY using AIKI air jet texturing machines, respectively. The processing parameters such as air pressure and yam speed are varied, and air pressure is varied ranging with 8.5bar, l0.5bar and 1l.5bar, and yarn speed is varied ranging with 400m/mim, 450m/mim, and 500m/min. The various physical properties of ATY made by POY and FDY denier, wet shrinkage, dry shrinkage, tensile properties, thermal stress and instability are measured and discussed with air pressure and yam speed. The shrinkage simulation of ATY is performed for analysing the process shrinkage on the dyeing and finishing processes.

• Fibers and Polymers
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• 제7권4호
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• pp.372-379
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• 2006

The surface topography, tensile properties, and thermal properties of ramie fibers were investigated as reinforcement for fully biodegradable and environmental-friendly 'green' composites. SEM micrographs of a longitudinal and cross sectional view of a single ramie fiber showed a fibrillar structure and rough surface with irregular cross-section, which is considered to provide good interfacial adhesion with polymer resin in composites. An average tensile strength, Young's modulus, and fracture strain of ramie fibers were measured to be 627 MPa, 31.8 GPa, and 2.7 %, respectively. The specific tensile properties of the ramie fiber calculated per unit density were found to be comparable to those of E-glass fibers. Ramie fibers exhibited good thermal stability after aging up to $160^{\circ}C$ with no decrease in tensile strength or Young's modulus. However, at temperatures higher than $160^{\circ}C$ the tensile strength decreased significantly and its fracture behavior was also affected. The moisture content of the ramie fiber was 9.9 %. These properties make ramie fibers suitable as reinforcement for 'green' composites. Also, the green composites can be fabricated at temperatures up to $160^{\circ}C$ without reducing the fiber properties.

• 한국토양비료학회지
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• 제25권3호
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• pp.220-230
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• 1992

우리나라에서 토양(土壤) 온도(溫度)를 정규적으로 관측(觀測)하고 있는 기상청(氣象廳) 산하(傘下) 기상대(氣象臺) 및 관측소(觀測所) 관측(觀測) 노장(露長)의 토양시료(土壤試料)를 채취(採取)하여 토양(土壤)의 열전도(熱傳度) 특성(特性)과 관련이 깊은 토양(土壤)의 용적밀도(容積密度), 토성(土性), 유기물(有機物) 함량(含量) 등 물리적(物理的) 특질(特質)을 분석(分析)하였으며, 토양(土壤)의 열확산(熱擴散) 계수(係數)를 산출(算出)하였다. 기상청(氣象廳) 산하(傘下) 기상대(氣象臺) 및 관측소(觀測所) 토양(土壤)의 물리적(物理的) 특성(特性)을 조사한 결과(結果) 0-10cm의 표토(表土)는 52%가 사양토(砂壤土)였으며, 양토(壤土)와 미사질양토(微砂質壤土)가 38%, 그리고 식양토(埴壤土) 및 미사질식토(微砂質埴土)가 10%이었다. 이들 토양(土壤)의 열특성(熱特性)과 관계가 깊은 용적밀도(容積密度)는 사토(砂土)가 $1.41g/cm^3$, 양토(壤土)와 미사질양토(微砂質壤土)가 $1.33g/cm^3$, 그리고 식양토9埴壤土) 및 미사질식토(微砂質埴土)가 $1.21g/cm^3$로 토성(土性)이 미세할수록 낮은 값을 보였다. 열확산(熱擴散) 계수(係數)는 평균(平均) $3.53{\times}10^{-3}cm^3/sec$이었으며, $1.159-8.401{\times}10^{-3}cm^3/sec$의 범위에 있었다. 특히 유기물(有機物) 함량(含量)이 높고 용적밀도(容積密度)가 낮은 제주도(濟州道) 토양(土壤)의 열확산(熱擴散) 계수(係數)는 표토(表土)에서 $2{\times}10^{-3}cm^3/sec$으로 다른 지역의 토양(土壤)보다 현저히 낮았다. 토심(土深) 30cm 이하(以下) 토양(土壤)의 열확산(熱擴散) 계수(係數)는 평균(平均) $6.81{\times}10^{-3}cm^3/sec$로 $1.54-16.12{\times}10^{-3}cm^3/sec$의 범위를 보여 표토(表土)보다 높았다. 열확산(熱擴散) 계수(係數)로부터 계산(計算)된 표토(表土)의 일주간(日週期) 불역심(不易深)(damping depth)은 5.92-13.65cm였으며, 깊이 30cm이하의 연주기(年週期) 불역심(不易深)은 124-342cm이었다. 한편, 실험실내(實驗室內)에서 열선막대법에 의하여 측정(測定)된 열확산9熱擴散) 계수(係數)와 용적밀도(容積密度) 및 토양수분함량(土壤水分含量)과의 관계로부터 열확산(熱擴散) 계수(係數)를 추정(推定)할 수 있는 중회귀(重回歸) 모델을 이용하면 토양온도(土壤溫度)가 부족한 지점(地點)의 열확산(熱擴散) 계수(係數)를 추정(推定)할 수 있게 되었다.

• 한국세라믹학회지
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• 제49권4호
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• pp.385-396
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• 2012

Thermal shock test methods and thermal shock parameters for ceramics were reviewed from the following viewpoints: (1) The test methods should be based on the precise estimation of both temperature and thermal stress distributions in a specimen taking into account the temperature-dependent thermo-mechanical properties; (2) The thermal shock parameters must be defined as a physical property of the materials and described as a function of temperature at the fracture point of the specimen; (3) The relation between the strength and fracture toughness of brittle ceramics under a thermal shock load must be the same as the relation under a mechanical load. In addition, appropriate thermal shock parameters should be defined by the thermal shock strength and thermal shock fracture toughness based on stress and energy criteria, respectively. A constant heat flux method is introduced as a testing technique suitable for estimating these thermal shock parameters directly from the electric power charged.

• 한국세라믹학회지
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• 제29권8호
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• pp.623-629
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• 1992

The possible use of bioglass as implant materials is due to its biocompatibility to human body. Even if many animal studies for the bioglasses have been performed, their compositional dependences of structures and physical properties are not fully understood. In the present work, physical property measurements such as density and thermal expansion coefficient were carried out for the bioglasses, with substitution of CaO for Na2O in bioglass composition (46.1%SiO2, 24.4%Na2O, 26.9%CaO, 2.6%P2O5:mol%). Hydroxyapatite formation on the glass surface was also examined after reacted in Tris-buffer solution. As CaO was substituted for Na2O, the bond strength between nonbridging oxygen and modifier became stronger to make glass structure rigid, and resulted in increase in density and decrease in thermal expansion coefficient. When the bioglasses were reacted in Tris-buffer solution, hydroxyapatite was formed on the bioglass surface for all prepared glasses in 2 hours, independently on CaO content, and the thickness of hydroxyapatite layer was decreased a little, while the thickness of SiO2 rich layer was decreased sharply with CaO content.

• 한국주조공학회지
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• 제43권3호
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• pp.107-136
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• 2023

주강품 사형주조에는 천연규사가 보편적으로 사용되었고, 규사의 열적특성 부족에 의한 소착결함 억제를 위해, 크로마이트사가 사용되기도 하였으나, 반복 사용에 의한 골재 열화, 시스템샌드 혼입 문제, 분리 제거의 어려움, 높은 밀도에 따른 조형 시 하중증가, 크롬 함유 폐기물이 되는 단점이 있다. 최근에는 주조업계의 중요한 과제로써 산업폐기물 저감 및 대기환경 개선이 부각되고 있다. 종래의 주물사 사용 시 발생되는 문제점 해결과 주조공장의 환경개선을 위해서, 천연사를 대체 적용할 수 있는 다양한 인공사가 개발되어 소개되고 있다. 인공사는 용융분사법으로 제조된 인공사와 조립소결법으로 제조된 인공사 및 분쇄법으로 제조된 인공사로 분류할 수 있으며, 원료광물의 종류, 제조공법에 따라 상이한 물리적 특성을 나타낸다. 본 연구에서는 각종 주물사의 물성, 주형강도, 물리적 내구성, 열적 내구성, 소착시험편 주조 등의 비교 평가시험을 하였다. 밀도에 따른 주물사 실사용량, 주물사 형상에 따른 주형강도, 주물사의 물리적 및 열적 내구성, 주물사의 내열특성을 종합적으로 고려하였을 때, 아크용사법으로 제조된 용융인공사 A1 또는 분말식화염용사법으로 제조된 용융인공사 B가 대형주강품 주조에 가장 적합한 구형의 인공사로 판단된다.

• 한국의상디자인학회지
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• 제20권4호
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• pp.163-174
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• 2018

Consumer and property evaluation of wetsuit materials were conducted to obtain useful data for developing competitive products that meet consumer expectations and improving industrial competitiveness. Data were collected through online surveys of 213 domestic consumers who have experienced wearing wetsuit among marine leisure activities. Five types of commercial wet suit materials by brand and four types of commercial wet suit materials with the same quality by thickness were collected. Then, their physical properties, salt water resistance and thermal insulation rate were evaluated and compared. As a result, the most commonly used wetsuit material is 3 to 5 mm thick, and the basic jersey material is bonded on both sides. As a processing for imparting functionality, processing for improving warmth and reducing surface resistance are most frequently used. Consumers often feel uncomfortable when wearing a wetsuit, such as wearing comfort, weight, ease of movement, stretchability, and clothing pressure, which are different from those of casual wear. Also, mechanical strength and warmth were considered to be the most important criteria for selection of wetsuit material for purchase or rental. The mechanical properties of brand A and B were better than those of brand C, D, and E. Resilience and thermal shrinkage were better in brand C, D, and E. On the other hand, there was no significant difference in the physical properties due to the difference in thickness of the material at the same quality. Also, it was found that the thicker the material, the more stable it is in the heat. Brand A and B had superior salt water resistance than brand C, D, and E. In the thermal insulation test, brand A and B showed better insulation characteristics than brand C, D, and E, but the types of bonded fabric and surface finishing of materials were thought to have affected. In comparison of the thickness, the thicker the materials, the better the salt resistance and the thermal insulation.

• 대한금속재료학회지
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• 제46권3호
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• pp.182-188
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• 2008

Carbon nanotubes(CNTs) have outstanding mechanical, thermal, and electrical properties. Thus, by placing nanotubes into appropriate matrix, it is postulated that the resulting composites will have enhanced properties. Cold spray can produce thick metal-based composite coatings with very high density, low oxygen content, and phase purity, which leads to excellent physical properties. In this study, we applied cold spray coating process for the consolidation of Cu/CNT composite powder. The precursor powder mixture, in which CNTs were filled into copper particles, was prepared to improve the distribution of the CNT in copper matrix. Pure copper coating was also conducted by cold spraying as a reference. Annealing heat treatment was applied to the coating to examine its effect on the properties of the composite coating. The hardness of Cu/CNT composite coating represented similar value to that of pure copper coating. It was importantly found that the electrical conductivity of the Cu/CNT composite coating significantly increased from 53% for the standard condition to almost 55% in the optimized condition, taking annealed ($500^{\circ}C/1hr$.) copper coating as a reference (100%). The thermal conductivity of Cu/CNT composite coating layer was higher than that of pure Cu coating. It was also found that the electrical and thermal conductivities of Cu/CNT composite could be improved through annealing heat treatment. The microstructural evolution of Cu/CNT coating was also investigated and related to the macroscopic properties.