• Title/Summary/Keyword: Material coefficient

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A Study of Interface Heat Transfer Coefficient Between Die and Workpiece for Hot Forging (열간단조시 금형과 소재간 계면열전달계수에 관한 연구)

  • Kwon J. W.;Lee J. H.;Lee Y. S.;Kwon Y. N.;Bae W. B.
    • Transactions of Materials Processing
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    • v.14 no.5 s.77
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    • pp.460-465
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    • 2005
  • The temperature difference between die and workpiece has been frequently caused to various surface defects. The distribution and change for the temperature of forged part should be analyzed to prevent the generation of various defects related with the temperature. The surface temperature changes were affected with the interface heat transfer coefficient. Therefore, the coefficient is necessary to predict the temperature changes of die and workpiece. In this study, the experimental and FE analysis were performed to evaluate the coefficient with a function of pressure, temperature, material, and etc. The closed die upsetting was used to measure the coefficient on pressure over the flow stress. AISI1045, A16061, and Cu-OFHC were used to analyze the effect of material. The coefficient was increased with step-up of pressure between die and workpiece. And, A16061 was larger than that of the AISI1045 and Cu-OFHC up to the five times.

A study of interface heat transfer coefficient between die and workpiece for hot forging (열간단조시 금형과 소재간 계면열전달계수에 관한 연구)

  • Kwon J.W.;Lee Y.S.;Kwon Y.N.;Lee J.H.;Bae W.B.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.05a
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    • pp.122-126
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    • 2004
  • The temperature difference between die and workpiece has been frequently caused to various surface defects. The distribution and change fur the temperature of forged part should be analyzed to prevent the generation of various defects related with the temperature. The surface temperature changes were affected with the interface heat transfer coefficient. Therefore, the coefficient is necessary to predict the temperature changes of die and workpiece. In this study, the experimental and FE analysis were performed to evaluate the coefficient with a function of pressure, temperature, material, and etc. The sealed die upsetting was used to measure the coefficient on pressure over the flow stress. AISI1045, Al6XXX, and Pure-Cupper were used to analyze effects according to the material. The coefficient was increased with step-up of pressure between die and workpiece. And, Al6XXX was larger than the AISI1045 and Pure-Cupper up to the five times.

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A Study on the Evaluation of Material Degradation for 2.25Cr-1Mo Steel by Ultrasonic Measurements (초음파 계측에 의한 2.25Cr-1Mo강의 열화도 평가에 관한 연구)

  • 박은수;박익근;김정석
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.10 no.3
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    • pp.61-67
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    • 2001
  • The remaining life estimation for the aged component is very important because mechanical properties of the compo-nents are degraded with time of service exposure in high temperature etc. The destructive method is widely used for the estimation of material degradation, but it has a difficulty in preparing specimens from in-service industrial facilities. In order to evaluate the feasibility of ultrasonic evaluation method for properties of high temperature materials, 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at 63$0^{\circ}C$ were evaluated by ultra-sonic measurements investigating the change of velocities and attenuation coefficient. In this results, attenuation coefficient was found to be sensitive to material degradation mainly attributed to the change of grain size and the precipitation of impurities in grain boundaries, but velocity was not for all specimens.

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Performance Evaluation for Piezoelectric Unimorph Actuator with Stress Distribution (응력 분포에 따른 압전 유니모프 작동기의 성능 평가)

  • Lee, Jong-Won;Kang, Lae-Hyoung;Han, Jae-Hung;Jung, Sang-Jun;Ko, Han-Young
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2008.04a
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    • pp.127-131
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    • 2008
  • This paper deals with the performance evaluation of piezoelectric unimorph actuator. In the unimorph design, the thickness ratio of substrate to piezoelectric material and the elastic modulus ratio of substrate to piezoelectric material are important parameters. There exists only one structural configuration that satisfies the optimal condition among them, and actuators using that configuration exhibit better actuating displacements. Another design parameter is the piezoelectric coefficient which can be improved due to the induced tensile stress and voltages. The application of the tensile stress to the piezoelectric material makes it get higher piezoelectric coefficient and the total displacement performance of the unimorph actuator is improved. Finally, the piezoelectric actuator system with spring elements is fabricated and it shows higher actuating displacement capability.

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Material Properties Characterization Based on Measurements of Reflection Coefficient and Bandwidth

  • Nguyen, Phuong Minh;Chung, Jae-Young
    • Journal of electromagnetic engineering and science
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    • v.14 no.4
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    • pp.382-386
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    • 2014
  • The knowledge of substrate material properties is important in antenna design. We present a technique to accurately characterize the dielectric constant and loss tangent of an antenna substrate based on the measurements of antenna's reflection coefficient and bandwidth. In this technique, an error function is formulated by combinations of the reflection coefficient and bandwidth of measured and simulated data, and then an optimization technique is used to efficiently search for the substrate properties that minimize the error function. The results show that the method is effective in retrieving the dielectric constant and loss tangent of the antenna substrate without the need of additional test fixtures as in conventional substrate characterization methods.

Double bonded Cooper-Naghdi micro sandwich cylindrical shells with porous core and CNTRC face sheets: Wave propagation solution

  • Yazdani, Raziye;Mohammadimehr, Mehdi
    • Computers and Concrete
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    • v.24 no.6
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    • pp.499-511
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    • 2019
  • In this paper, wave propagation of double-bonded Cooper-Naghdi micro sandwich cylindrical shells with porous core and carbon nanotube reinforced composite (CNTRC) face sheets are investigated subjected to multi-physical loadings with temperature dependent material properties. The governing equations of motion are derived by Hamilton's principle. Then, the influences of various parameters such as wave number, CNT volume fraction, temperature change, Skempton coefficient, material length scale parameter, porosity coefficient on the phase velocity of double-bonded micro sandwich shell are taken into account. It is seen that by increasing of Skempton coefficient, the phase velocity decreases for higher wave number and the results become approximately the constant. Also, by increasing of the material length scale parameter, the cut of frequency increases, because the stiffness of micro structure increases. The obtained results for this article can be used to detect, locate and quantify crack.

A study on the forming analysis of double-dome model considering CFRP prepreg laminate condition and coefficient of friction (CFRP Prepreg 적층조건과 금형 마찰계수를 고려한 Double-dome 형상 성형해석 연구)

  • Kim, Young-Ju;Lee, San-Ho;Kim, Heung-Kyu
    • Design & Manufacturing
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    • v.10 no.2
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    • pp.12-17
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    • 2016
  • Recently, lightweight material is attracting attention as a solution to the problem of fuel efficiency and increasing the need for development. CFRP has been attracting attention as lightweight materials for automobile because it has a high specific stiffness and specific strength compared to steel material. CFRP have a wide range of mechanical properties depending on the laminate condition. In this paper, study on the forming analysis of double-dome model was performed considering CFRP prepreg laminate condition and coefficient of friction. After forming analysis, the result has compared with wrinkling area and vertical strain of fiber to the laminated condition. And then compared with inflow of blank to the laminate condition. Through this paper, we propose the forming analysis methods of CFRP material.

The effect of solid lubricant on the frictional characteristics of Cu base sintered friction material. (소결 마찰재의 마찰특성에 미치는 고체 윤활제의 영향)

  • 정진현;이범주;조정환;정동윤;권석진
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1996.04b
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    • pp.45-54
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    • 1996
  • The effect of graphite on the frictional characteristics of Cu-based sintered friction materials was studied by pin-on-disk type wear test. A study has been carried out concerning the optimum concentration of graphite in sintered friction material to obtain the minimum wear rate and low friction coefficient . Friction coefficient and wear rate were increased as increasing the content of graphite in the matrix. In the study the optimum concentration of graphite was 19vol % to get the minimum wear rate and optimal frick'ion coefficient.

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The study on the estimation of diffuse field absorption coefficient by using normal incidence impedance (수직입사 임피던스를 이용한 난입사 흡음율 예측 연구)

  • 유승국;김영찬;김두훈
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1998.04a
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    • pp.643-649
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    • 1998
  • This paper is to compare the absorption coefficient with normal incidence waves and it with diffuse incidence waves of glass wool which the most used absorption material and multi layer fiber. The absorption coefficient with normal incidence waves is calculated by surface impedance that measured by using an acoustic tube. Based on this data, the absorption. coefficient with diffuse incidence waves is predicted and is compared with measured the absorption coefficient in reverberation room.

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The Microstructure and Electrical Characteristics of Pr-Based ZnO Variators with $La_2O_3$Additives ($La_2O_3$가 첨가된 Pr계 ZnO 바리스터의 미세구조와 전기적 특성)

  • 남춘우;박춘현
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.11 no.11
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    • pp.969-974
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    • 1998
  • The effects of $La_2O_3$on the microstructure and electrical characteristics of Pr-based ZnO varistors were investigated. The average grain size increased in the range of 21.9~56.3$\mu$ m with increasing $La_2O_3$additive content(0.0~2.0 mol%). La was, of course grain boundary, largely segregated at the nodal point. As $La_2O_3$additive content increases, threshold voltage and nonlinear coefficient decreased and leakage current increased. In particular, 2.0 mol% $La_2O_3$-added varistor exhibited low threshold voltage 17.0V/mm and nonlinear coefficient of about 6. Based on these results, this varistor can be said to be used as low-voltage varistor, if nonlinear coefficient is somewhat improved forward.

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