• Title/Summary/Keyword: Thermal Hysteresis

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An Analysis Finite Element for Element for Elasto-Plastic Thermal Stresses Considerating Strain Hysteresis at Quenching Process of Carbon Steel (I) - Analysis of temperature distribution - (탄소강의 담금질 처리과정에서 변형율이력을 고려한 탄소성열응력의 유한요소 해석(I) - 온도분포의 해석 -)

  • Kim, Ok-Sam;Cho, Eui-Il;Koo, Bon-Kwon
    • Journal of the Korean Society for Heat Treatment
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    • v.8 no.3
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    • pp.213-221
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    • 1995
  • Temperature distribution, transformation and residual stresses generated during the quenching process of carbon steel. It follows many difficulties in the analytical considerations on those quenching process because of the coupling effects on temperature and metallic structures. In this paper one of the basic study on the quenching stresses was carried out for the case of the round steel bar specimen(SM45C) with 40mm both in its diameter and length. The temperature distributions considering strain hysteresis were numerically calculated by finite element technique. In calculating the transient temperature field, the heat flux between water and rod surface was determined from the heat transfer coefficient. The gradient of temperature is almost same to geometric of specimen. At early stage of the quenching process, the abrupt temperature gradient has been shown in the surface of the specimen.

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The Fabrication of Ferroelectric PZT thin films by Sol-Gel Processing (졸-겔법에 의한 강유전성 PZT 박막의 제작)

  • Lee, B.S.;Chung, M.Y.;You, D.H.;Kim, Y.U.;Lee, S.H.;Lee, N.H.;Ji, S.H.;Park, S.H.;Lee, D.C.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2002.05c
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    • pp.93-96
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    • 2002
  • In this study, PZT thin films were fabricated using sol-gel processing onto Si/$SiO_2$/Ti/Pt substrates. PZT sol with different Zr/Ti ratio(20/80, 30/70, 40/60, 52/48) were prepared, respectively. The films were fabricated by using the spin-coating method on substrates. The films were heat treated at $450^{\circ}C$, $650^{\circ}C$ by rapid thermal annealing(RTA). The preferred orientation of the PZT thin films were observed by X-ray diffraction(XRD), and Scanning electron microscopy(SEM). All of the resulting PZT thin films were crystallized with perovskite phase. The fine crystallinity of the films were fabricated. Also, we found that the ferroelectric properties from the dielectric constant of the PZT thin films were over 600 degrees, P-E hysteresis constant. And the leakage current densities of films were lower than $10^{-8}A/cm^2$. It is concluded that the PZT thin films by sol-gel process to be convinced of application for ferroelectric memory device.

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An Experiment on Thermosyphon Boiling in Uniformly Heated Vertical Tube and Asymmetrically Heated Vertical Channel

  • Kwak, Ho-Young;Jeon, Jin-Seok;Na, Jung-Hee;Park, Hong-Chul
    • Journal of Mechanical Science and Technology
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    • v.15 no.1
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    • pp.98-107
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    • 2001
  • Continuing efforts to achieve increased circuit performance in electronic package have resulted in higher power density at chip and module level. As a result, the thermal management of electronic package has been important in maintaining or improving the reliability of the component. An experimental investigation of thermosyphonic boiling in vertical tube and channel made by two parallel rectangular plates was carried out in this study for possible application of the direct immersion cooling. Fluorinert FC-72 as a working fluid was used in this experiment. Asymmetric heated channel of open periphery with gap size of 1, 2, 4 and 26mm and uniformly heated vertical tubes with diameter of 9, 15 and 20mm were boiled at saturated condition. The boiling curves from tested surfaces exhibited the boiling hysteresis. It was also found that the gap size is not a significant parameter for the thermosyphonic boiling heat transfer with this Fluorinert. Rather pool boiling characteristics appeared for larger gap size and tube diameter. The heat transfer coefficients measured were also compared with the calculation results by Chens correlation.

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Analysis of Steady Heat Conduction for Rubber Pads of a Tank Track Subjected to Dynamic Loading (동적하중을 받는 궤도차량 고무패드의 정상 열전도 해석)

  • Kim, Hyung-Je;Kim, Byung-Tak
    • Elastomers and Composites
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    • v.36 no.3
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    • pp.153-161
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    • 2001
  • The rubber pads era tank which undergo dynamic deformations with the sufficient amplitudes and frequencies lead to a considerable internal temperature rise due to the heat generation. The heat generation which is dependent on the viscoelastic characteristics or a rubber is due to the conversion of partial mechanical energy into thermal energy identical to the area oi hysteresis loop. Heat generation without adequate heat dissipation leads to heat build-up and the excessive temperature rite exerts a bad influence upon the performance and the life of rubber products. In this paper, temperature distributions of the rubber pads of a tank track subjected to dynamic loads are obtained under the assumption of the steady state. Heat generation rates used in this finite element analysis are acquired through experiments and the computed temperature fields are displayed in isothermal contour regions.

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Performance Loss & Heat Transfer Characteristics of Synchronous Motors under Various Driving Conditions (구동 조건 변화에 따른 동기 전동기의 성능 손실 및 내부 열전달 특성)

  • Choi, Moon Suk;Um, Sukkee
    • Transactions of the Korean Society of Automotive Engineers
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    • v.21 no.3
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    • pp.165-173
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    • 2013
  • Core loss has a major effect on heat generation in synchronous motors with surface-mounted permanent magnets (SPMs). It is essential to perform heat transfer analysis considering core loss in SPM because core loss is seriously affected by torque and speed of motors. In the present study, mechanical loss, core loss and coil loss are evaluated by measuring input and output energies under various driving conditions. For a better understanding heat transfer paths in synchronous motors, we developed a lumped thermal system analysis model. Subsequently, heat transfer analysis has been performed based on acquired energy loss, temperature data and thermal resistance with three types of SPM. It is shown that the torque constants decrease by Max. 10% as speed increase. At the rated torque, the core loss is Max. 10.9 times greater than the coil loss and the hysteresis loss of magnets is dominant in total loss.

Effects of NH3 on the Growth of Oxide Film by Infrared-CVD Method (적외선 CVD 방법을 이용한 산화막 성장에 $NH_3$가 미치는 영향)

  • Lee, Chul-Seung;Chung, Kwan-Soo;Kim, Chul-Ju
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.25 no.11
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    • pp.1329-1334
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    • 1988
  • A new method was developed for growing oxidation film by thermal reaction of $NH_3$ and $O_2$. The growth rate increased with the increase of partial pressure of $NH_3$. Optical transparency of the growth film was 12% at the wave number 1100 $cm^{-1}$ compared with 17% by thermal dry oxidation method, and the quality was much better. In C-V characteristic curve, $Q_{OX}$ was almost equal to $Q_{SS}$ and no hysteresis phenomena was observed. n-MOS transistors fabricated with this new method showed $I_D$-$V_{DS}$ characteristics better than thermal dry oxidation method.

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Effect of interface bonding strength on the recovery force of SMA reinforced polymer matrix smart composites (형상기억합금 선재가 삽입된 폴리머기지 능동복합재료의 회복력에 미치는 계면 접합강도의 영향)

  • 김희연;김경섭;홍순형
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2003.04a
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    • pp.18-21
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    • 2003
  • The effect of interface bonding strength on the recovery force of SMA wire reinforced polymer matrix composites was investigated by pullout test. Firstly, the recovery forces and transformation temperatures of various prestrained SMA wires were measured and 5% prestrained SMA wires were prepared for the reinforcements of composites. EPDM incorporated with 20vol% silicon carbide particles(SiCp) of 6, 12, $60{mutextrm{m}}$ size were used as matrix. Pullout test results showed that the interface bonding strength increased when the SiCp size decreased due to the increase of elastic modulus of matrix. Cyclic test of composites was performed through control of DC current at the constant displacement mode. The abrupt decrease of recovery force during cycle test at high current was occurred by thermal degradation of matrix. This was in good agreement with temperature related in the thermal degradation of matrix. The hysteresis of recovery force with respect to the temperature was compared between wire and composite and the hysterisis of composites was smaller than the wire due to less thermal conduction.

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Effects of Thermal Heat Treatment Process on the Ferroelectric Properties of ReMnO3 (Re:Ho, Er) Thin Films (ReMnO3(Re:Ho, Er) 박막의 강유전성에 미치는 열처리 공정의 영향)

  • Kim, Eung-Soo;Chae, Jung-Hoon
    • Journal of the Korean Ceramic Society
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    • v.42 no.11 s.282
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    • pp.763-769
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    • 2005
  • Ferroelectric $ReMnO_3$(Re:Ho, Er) thin films were deposited on Si(100) substrate by Metal-Organic Chemical Vapor Deposition (MOCVD). Crystallinity and electric properties of $ReMnO_3$(Re:Ho, Er) thin films were investigated as a function of thermal heat treatment process, CHP (Conventional Heat-treatment Process) and RTP (Rapid Thermal Process). $ReMnO_3$(Re:Ho, Er) thin films prepared by RTP showed higher c-axis preferred orientation and homogeneous surface roughness than those prepared by CHP. The remnant polarization of ferroelectric hysteresis loop of $ReMnO_3$(Re:Ho, Er) thin films was strongly dependent on the c­axis preferred orientation of hexagonal single phase, and the leakage current characteristics of thin films were dependent on the homogeneity of grain size as well as surface roughness of thin films.

Thermo-Mechanical Properties of Al2TiO5 Ceramics Stabilized with MgO and ZrO2 Additives (MgO와 ZrO2가 첨가된 Al2TiO5 세라믹의 열·기계적 물성)

  • Kim, Da-Mi;Kim, Hyung-Tae;Kim, Hyeong-Jun;Kim, Ik-Jin;Choi, Seong-Cheol;Kim, Yong-Chan;NamKung, Jung;Ryu, Sung-Soo
    • Journal of Powder Materials
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    • v.19 no.4
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    • pp.253-258
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    • 2012
  • The characteristics of $Al_2TiO_5$ ceramics were influenced by the additives and the heat treatment that controls the microcrack behavior at grain boundaries. The effect of additives on $Al_2TiO_5$ ceramics were investigated in terms of mechanical properties and thermal expansion at high temperature. The $Al_2TiO_5$ were synthesized at $1500^{\circ}C$, $1550^{\circ}C$ and $1600^{\circ}C$ for 2h by reaction sintering. The formation of $Al_2TiO_5$ phase was increased by additives that enhanced the volume of the microcrack that can lead to low thermal expansion. The mechanical properties of the stabilized $Al_2TiO_5$ ceramics were increased remarkably at $1100^{\circ}C$, $1200^{\circ}C$ and $1300^{\circ}C$ due to the oneset of mechanical healing of grain-bondary microcracks at a high temperature. The amount of microcrack was decreased at lower sintering temperature that causes the increase of mechanical properties at high temperature.

Electrical properties of metal-oxide-semiconductor structures containing Si nanocrystals fabricated by rapid thermal oxidation process (급속열처리산화법으로 형성시킨 $SiO_2$/나노결정 Si의 전기적 특성 연구)

  • Kim, Yong;Park, Kyung-Hwa;Jung, Tae-Hoon;Park, Hong-Jun;Lee, Jae-Yeol;Choi, Won-Chul;Kim, Eun-Kyu
    • Journal of the Korean Vacuum Society
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    • v.10 no.1
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    • pp.44-50
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    • 2001
  • Metal oxide semiconductor (MOS) structures containing nanocrystals are fabricated by using rapid thermal oxidations of amorphous silicon films. The amorphous films are deposited either by electron beam deposition method or by electron beam deposition assisted by Ar ion beam during deposition. Post oxidation of e-beam deposited film results in relatively small hysteresis of capacitance-voltage (C-V) and the flat band voltage shift, $\DeltaV_{FB}$ is less than 1V indicative of the formation of low density nanocrystals in $SiO_2$ near $SiO_2$/Si interface. By contrast, we observe very large hysteresis in C-V characteristics for oxidized ion-beam assisted e-beam deposited sample. The flat band voltage shift is larger than 22V and the hysteresis becomes even broader as increasing injection times of holes at accumulation condition and electrons at inversion condition. The result indicates the formation of slow traps in $SiO_2$ near $SiO_2$/Si interface which might be related to large density nanocrystals. Roughly estimated trap density is $1{\times}10^{13}cm^{-2}$. Such a large hysteresis may be explained in terms of the activation of adatom migration by Ar ion during deposition. The activated migration may increase nucleation rate of Si nuclei in amorphous Si matrix. During post oxidation process, nuclei grow into nanocrystals. Therefore, ion beam assistance during deposition may be very feasible for MOS structure containing nanocrystals with large density which is a basic building block for single electron memory device.

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