• Title/Summary/Keyword: Material coefficient

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Effect of Humidity on Friction Characteristics of Automotive Friction Materials

  • Kim, Seong-Jin;Lee, Jae-Young;Jang, Ho
    • KSTLE International Journal
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    • v.2 no.2
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    • pp.150-153
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    • 2001
  • The effects of humidity on friction performance of automotive brake materials were studied using a pad-on-disk type friction tester. Three different friction materials based on a simple formulation were investigated by changing the solid lubricant graphite, MoS$_2$, and Sb$_2$S$_3$. Friction materials without solid lubricants were also examined to study the effect of other ingredients in the matrix on humidity. The friction material containing graphite was strongly affected by the humidity showing lower friction coefficient at high humidity level than other conditions. On the other hand, the friction material containing MoS$_2$exhibited higher friction coefficient at initial stage under high humidity level. The friction material without solid lubricant or with Sb$_2$S$_3$ was not affected by humidity conditions. However, the friction material containing barite showed strong speed dependence.

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Tribological Characteristics for High Perfomance Metallic Friction Materials (고성능 금속마찰재의 트라이볼로지적 특성)

  • 김석삼;김재호;안효준
    • Tribology and Lubricants
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    • v.14 no.1
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    • pp.45-53
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    • 1998
  • Friction and wear test for two kinds of Cu-based sintered metallic friction material against cast iron disk was carried out by plate-on-disk type friction and wear tester to investigate the friction and wear characteristics of brake system in severe condition. In this experimental study, the counter specimen was cast iron which is being used generally in brakes of heavy duty equipments. Test friction materials were A type which was manufactured by foreign company and B type by domestic company. Friction coefficient and wear volume were measured and compared with each other. The experiment was performed under room temperature. The worn surface of cast iron disk and friction material were observed by scanning electron microscope. The temperature of surface of disk was measured continuously by the non-contacting thermometer. It was found that A type friction material had stable friction coefficient over the wide range of sliding condition, but B type friction material had unstable friction coefficient and lower value of 0.2 under the severe sliding condition.

Estimation of Roughness Coefficient Using a Representative Grain Diameter for Han Stream in Jeju Island (한천의 대표입경을 이용한 조도계수 산정)

  • Lee, Jun-Ho;Yang, Sung-Kee;Kim, Dong-Su
    • Journal of Environmental Science International
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    • v.22 no.5
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    • pp.563-570
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    • 2013
  • Roughness coefficient was computed for review of applicability based on measurement of the representative grain diameter reflecting channel characteristics of Han Stream. After field survey, collection of bed material, and grain analysis on the collected bed material, roughness coefficient was computed using representative grain and existing empirical equation for roughness coefficient. Value of roughness coefficient calculated using equation by Meyer-Peter and Muller (1948) was 0.0417 for upstream, 0.0432 for midstream, and 0.0493 for downstream. As a result of comparing the computed roughness coefficient to other empirical equations for review of applicability, the coefficient was larger in Strickler (1923) equation by 0.006. Smaller coefficient was shown by Planning Report for River Improvement Works. Equation by Garde and Raju (1978) was larger by 0.004, and equations by Lane and Carlson (1953) and by Meyer-Peter and Muller (1948) were larger by 0.001. Such precise roughness coefficient is extremely important when computing the amount of flood in rivers to prevent destruction of downstream embankments and property damages from flooding. Since roughness coefficient is a factor determined by complicated elements and differs according to time and space, continued management of roughness coefficient in rivers and streams is deemed necessary.

The Decision on the Thermal Expansion Coefficient of the Glass Infiltrated in All Ceramic Crown (전부도재관 제작용 침투유리의 열팽창계수의 결정)

  • 김병수;이득용;김학관;장주웅
    • Journal of the Korean Ceramic Society
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    • v.40 no.1
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    • pp.93-97
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    • 2003
  • Using alumina-glass infiltrated material which has been in the spotlight of biomaterials including dental material, appropriate composition of glass infiltrated material mainly depends on the thermal expansion coefficient. To obtain proper compositional glass of suitable thermal expansion coefficient effiiently. a Taguchi analysis was conducted. The influence of alkali oxide and alkali earths oxide, which affect mostly the thermal expansion coefficient of glass infiltrated material, was infiltrated material, the effect having influenced on the thermal expansion coefficient of glass was presented in this order (Na$_2$O≫K$_2$O ≫MgO≒CaO). The effect of Na$_2$O was about eight times as great as the effects of MgO, CaO and $K_2$O was about four times. Among the interaction affects of each variables the interaction affects of $K_2$O-CaO showed most significantly and thermal expansion property of specified composition was predicted by calculating contribution rate on each level of variables and interaction affects.

Effect of Vibrational Amplitude on Friction and Wear Properties of Magnetorheological Elastomer (진폭에 따른 자기유변탄성체의 마찰 특성 연구)

  • Lian, Chenglong;Lee, Kwang-Hee;Lee, Chul-Hee
    • Tribology and Lubricants
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    • v.32 no.2
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    • pp.39-43
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    • 2016
  • Magnetorheological elastomers (MREs) are a type of “smart” material, and their properties can be controlled rapidly and reversibly under the influence of an external stimulus. The application of an external magnetic field can change the shear modulus, hardness, and friction coefficient of MREs. The friction can cause vibration; moreover, the vibration can affect friction. The change of friction depends on the relative motion, normal force, roughness of the rubbing surfaces, material type, temperature, lubrication, relative humidity, and vibration condition. As MREs are a type of “smart material,” their friction coefficient can be reduced by applying an external magnetic field—the applications of this feature in engineering have been widely studied. However, the friction properties of MREs under vibration have not been tested to date. In this study, MRE samples and a reciprocating friction tester were fabricated. The friction coefficient was measured to evaluate the friction properties under various vibration conditions; subsequently, the wear depth and wear surface profile of the MRE were observed in order to evaluate the wear properties. The results show that the friction coefficient of the MREs decreased when a magnetic field was applied. Moreover, the friction coefficient decreased when the vibrational amplitudes increased. The wear depth of the MRE also decreased as the vibrational amplitudes increased.

Correlation Analysis of the Dielectric Breakdown Voltage of Liquid Nitrogen (액체질소 절연파괴전압의 상관 분석)

  • Baek, Seung-Myeong
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.28 no.6
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    • pp.396-399
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    • 2015
  • We analyzed the correlation between breakdown voltage(BDV) of liquid nitrogen(LN2) and factors. The chosen factors affecting the breakdown are the diameter of electrode, gap length, temperature of LN2, and pressure of LN2. The BDV of LN2 was increased with increasing the diameter, the gap length and the pressure. And The BDV of LN2 was increased with decreasing the temperature. However, correlation coefficient was different from each other depending on the situation. The BDV exhibited a very high correlation coefficient of 0.92227 to dependence on the diameter. And a very high correlation coefficient of 0.94980 to dependence on the pressure under sphere(D 7.5 mm)-plane electrode. When the pressure is applied, sphere-plane electrode is the correlation coefficient was higher than that of the needle-plane electrode. It shows the dependence of a temperature coefficient of -0.758290 ~ -0.39946 under needle-plane electrode.

The Accurate design of a Temperature stable Dielectric Stepped-Impedance Resonator (온도 변화에 안정한 유전체 Stepped-Impedance Resonator의 정확한 설계)

  • 임상규;김덕환안철
    • Proceedings of the IEEK Conference
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    • 1998.10a
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    • pp.625-628
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    • 1998
  • This paper presents the design method of a temperature stable stepped-impedance resonator using composite material. In this method temperature coefficient of dielectric constant $(\tau\varepsilon)$ and thermal expansion coefficient $(\alpha1)$ of dielectric material were considered. Ba(Zn1/3Nb2/3)O3 and CaZrO3 as composite material having opposite signs of temperature coefficient of dielectric constant were selected. The length of this resonator for the temperature stability of resonance frequency was calculated at 900MHz, 1.4㎓ and 1.9㎓. It was found that the ratio of the length of positive $\tau\varepsilon$ materal to the length of negative $\tau\varepsilon$ material is constant at various resonance frequencies.

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Measurement of Reflection Coefficient of Sound Absorbent Material with Respect to Angle of Incidence and Its Associated Errors (입사각에 따른 흡음재의 반사 계수 측정 방법론 및 오차에 대한 고찰)

  • 이수열;김상렬;김양한
    • Journal of KSNVE
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    • v.4 no.3
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    • pp.295-305
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    • 1994
  • The reflection coefficient of a material at oblique incidence is measured in a free field. The sound pressure distributions are measured at discrete points on two measurement lines and then decomposed into plane wave components by using spatial Fourier transform. The inciedent and reflected plane wave components are obtained from a set of "decomposition equations" of which uses the plane wave propagation theory. Numerical simulations and experiments have been performed to see the effect of finite size of measurement area. To reduce this effect, a window fuction has been performed to see the effects of finite size of mesurement area. To reduce this effect, a window function has been proposed and its effect on the measurement of sound absorbing material property has been studied as well. The reflection coefficient obtained by this method is compared with those obtained from other methods; 2-microphone method in a duct and an expirical equation of which determines the characteristic impedance .rho.c and propagation constant k of a material from flow resistance information.formation.

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Effect of Humidity on Friction Characteristics of Automotive Friction Material (습도에 따른 자동차용 마찰재의 마찰특성에 관한 연구)

  • Kim, Seong-Jin;Choi, Nak-Cheon;Jang, Ho
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1998.10a
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    • pp.323-329
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    • 1998
  • The effect of humidity on friction characteristics of friction materials were studied using a pad-on-disk type friction tester. Three different friction materials containing simplified ingredients were investigated by changing the solid lubricant, graphite, MoS$_2$, and $Sb_2S_3$. A friction material without solid lubricant was also examined to study the effect of ingredients in the matrix on humidity. Friction material containing graphite showed lower friction coefficient at high humidity level than other conditions, however, friction material containing MoS$_2$ indicated higher friction coefficient at initial stage under high humidity level. Friction materials without solid lubricant and with $Sb_2S_3$ were little affected by humidity conditions.

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A study on the new absorption material for anechoic water tank (무향수조를 위한 흡음재질에 관한 연구)

  • Kim, Sung-Boo;Lee, Jong-Kyu
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.48 no.2
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    • pp.174-179
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    • 2012
  • A new absorption material, cellulose sponge soaked in cement, was made for anechoic water tank and its acoustical properties were investigated by pulse methods. The sound absorption coefficient a (dB/cm) of the material was obtained in the frequency range of 40~120kHz from the echo reduction ER (dB) and insertion loss IL (dB) data. The result was averagely 1.8dB/cm higher than the sound absorption coefficient a (dB/cm) of cork-filled rubber which is one of the most effective absorption materials. The wedge (1.2~5.0cm long) type absorption tiles were made with this new material. The echo reduction ER (dB) of the absorption tile with 5.0cm wedge measured in water tank was higher than 20dB in the experimental frequency range.