• Title/Summary/Keyword: expansion behavior

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Fabrication and Mechanical Properties of Cordierite/$ZrO_2$ Composites by Pressureless Sintering

  • Enhai Sun;Choa, Yong-Ho;Tohru Sekino;Koichi Niihara
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 2000.06a
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    • pp.233-242
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    • 2000
  • Cordierite/ZrO$_2$ composites with 5 to 25wt% ZrO$_2$ were fabricated by prssureless sintering, and their densification behavior, fracture strength, fracture toughness, microstructure and thermal expansion behavior were studied. The ZrO$_2$ addition into cordierite matrix affects the densification behavior and mechanical properties of the composites. By dispersing 25wt% ZrO$_2$, densified cordierite/ZrO$_2$ composite with a relative density of 98.5% was obtained at optimum sintering condition of 144$0^{\circ}C$/2H. Both fracture strength and toughness were increased from 140 to 290MPa and from 1.6 to 3.5 MPam$\frac{1}{2}$, respectively, by dispersing 25wt% ZrO$_2$ into the cordierite matrix. ZrO$_2$ particles were homogenously dispersed into cordierite matrix, which intragranular particles were fine(<100nm) and intergranular particles were coarse. The toughening mechanisms in the present composites were mainly attributed to martensitic transformation toughening. Then, the addition of ZrO$_2$ is likely to have little deleterious effect upon thermal expansion coefficient of cordierite.

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Microstructure and High Temperature Deformation Behavior of Heat Resistant Stainless Steel for a Retort (열환원반응관용 내열강의 미세조직과 고온변형거동)

  • Choi, G.S.;Ha, T.K.
    • Transactions of Materials Processing
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    • v.22 no.3
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    • pp.165-170
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    • 2013
  • High temperature deformation behavior of a heat-resistant duplex stainless steel, used as a retort in the Pidgeon process for Mg production, was investigated in this study. 25Cr-8Ni based duplex stainless steels were cast into rectangular ingots, with dimensions of $350mm{\times}350mm{\times}100mm$. Nitrogen and yttrium were added at 0.3wt.% each to enhance the heat-resistance of the steel. Phase equilibrium was calculated using the thermodynamic software FactSage$^{(R)}$ and the database of FSStel. For comparison, cast 310S steel, a widely used heat-resistant austenitic stainless steel, was also examined in this study. Dilatometry was conducted on the as-cast ingots for the temperature range from RT to $1200^{\circ}C$ and the thermal expansion coefficients were evaluated. The nitrogen addition was found to have an effect on the thermal expansion behavior for temperatures between 800 and $1000^{\circ}C$. High temperature tensile and compression tests were conducted on the ingots for temperatures ranging from 900 to $1230^{\circ}C$, which is the operation temperature employed in Mg production by the Silico-thermic reduction process. The steel containing both N and Y showed much higher strength as compared to 310S.

Behavior of Bridge Bearings for Railway Bridges under Running Vehicle

  • Choi, Eun-Soo;Yu, Wan-Dong;Kim, Jin-Ho;Park, Sun-Hee
    • International Journal of Railway
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    • v.5 no.1
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    • pp.10-21
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    • 2012
  • Open steel plate girder (OPSG) bridges are the most prevalent railroad bridge type in Korea, constituting about 40% of all railroad bridges. Solid steel bearings, known as line type bearings, are placed in most OSPG railway bridges. However, the line type rigid bearings generate several problems with the bridge's dynamic behavior and maintenance in service. To compare and investigate the dynamic behaviors of line type, spherical and disk bearings, the vertical displacements of each bearing, including fixed and expansion type, under running vehicles are measured and analyzed. The displacements of disk and spherical bearings are measured after replacing the line type bearings with spherical and disk bearings. This study also analyzed dynamic behaviors of bridges. Furthermore, the deformation of the PTFE (Polytetrafluoroethylene) plate that is placed inside of expansion type spherical and disk bearings is measured and its effect on the dynamic behavior of the bridges is discussed. The up-lift phenomenon at the bearings installed for the steel bridges is estimated. The vertical displacements at mid-span of the bridges are compared according to the bearing types. Finally, the 1st mode natural frequencies are estimated, and the relationship to the vertical displacement is discussed.

A Study of Interpretation of Separation Behavior in Gas Expansion Separation(GES) Bolt (가스팽창분리형 볼트 분리거동 해석 연구)

  • Kim Dong Jin;Lee Yeung Jo;Kang Won Kyu
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2004.10a
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    • pp.95-98
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    • 2004
  • The present work has been developed the study of interpretation of separation behavior in gas expansion separation(GES) bolt which has the separation characteristic without fragmentation and minimum pyre-shock during the operation of the explosive bolt. In order to obtain the performance of minimum pyro-shock, the present work used non-compressive material instead of separation explosives. The use of the interpretation processor could be extensively helped to design the shape and the amount of explosives in the explosive bolt having complex geometry, and to analyse the separation behavior during the operation. It is also proved that the GES bolt is the most suitable the separation system necessary to minimum pyro-shock and non fragmentation compare to others.

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Irradiation Behavior of Reactor Pressure Vessel SA508 class 3 Steel Weld Metals (압력용기강재 SA508 class 3 용착금속의 조사거동)

  • Koh, Jin-Hyun;Park, Hyoung-Keun;Kim, Soo-Sung;Hwang, Yong-Hwa;Seo, Yun-Seok
    • Journal of Welding and Joining
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    • v.28 no.5
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    • pp.69-74
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    • 2010
  • Irradiation behavior of the reactor pressure vessel SA508 class 3 steel weld metals was examined by Charpy V Notch impact specimens. The specimens were exposed to a fluence of $2.8{\times}1019$ neutrons(n)/$cm^2$(E>1 MeV) at $288^{\circ}C$. The irradiation damage of weld metal was evaluated by comparison between unirradiated and irradiated specimens in terms of absorbed energy and lateral expansion. The specimens for neutron irradiation were welded by submerged arc welding process at a heat input of 3.2 kJ/mm which showed good toughness in terms of weld microstructure, absorbed energy and lateral expansion. The post-irradiation Charpy V notch 41J and 68J transition temperature elevation were $65^{\circ}C$ and $70^{\circ}C$, respectively. This elevation was accompanied by a 20% reduction in Charpy V notch upper shelf energy level. The lateral expansion at 0.9mm irradiated Charpy specimens showed temperature elevation of $65^{\circ}C$ and was greatly decreased due to radiation damage.

Experimental Study on Tension-Hardening and Softening Characteristics in Reinforced Mortar with CSA Expansion Agent (CSA 팽창재를 혼입한 철근보강 모르타르의 인장 경화-연화 특성에 관한 실험적 연구)

  • Choi, Se-Jin;Ahn, Jung-Kil;Park, Ki-Tae;Kwon, Seung-Jun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.18 no.1
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    • pp.101-110
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    • 2014
  • Expansion agent is a very effective admixture for prevention of cracking due to autogenous/drying shrinkage and this can induce internal chemical prestress to embedded reinforcement. In this paper, tension-softening and hardening in cement mortar with steel and CSA expansion agent are experimentally evaluated. Cement mortar with steel reinforcement is prepared and tensile strength test is performed for evaluation of cracking and tensile behavior. In spite of slightly reduced strength and elasticity in CSA mortar, significantly increased tension-hardening behavior is evaluated in CSA mortar with induced chemical prestress. Furthermore previous tension softening models are compared with the test results and improvement are proposed.

A Study on the Influence of its Constituents on the Creep Behavior of High Temperature Composite Materials (고온용 복합재료의 크립 거동에 있어서 구성요소의 영향에 대한 연구)

  • 박용환
    • Journal of the Korean Society of Safety
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    • v.13 no.2
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    • pp.45-53
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    • 1998
  • A method to predict the creep behavior of fiber-reinforced ceramic composites at high temperatures was suggested based on finite element modeling using constituent creep equations of fiber and matrix and showed good agreement with the experimental results. The effects of matrix creep behavior, fiber volume fraction, and residual stresses on the composite creep behavior were also investigated. The results showed that the primary behavior of composites was greatly affected by that of matrix but post-primary behavior was governed by fiber creep characteristics. The increase of fiber volume fraction from 15 vol% to 30 vol% caused the 50% and 40% decrease of steady-state creep rates and total creep strains at $1200^{\circ}C$, 180MPa, respectively. Feasible compressive residual stresses in the matrix caused by different thermal expansion coefficients between the fiber and the matrix could significantly reduce total creep strains of the composite. The creep deformation mechanism in the fiber-reinforced ceramic composites could be explained by the stress transfer and redistribution in the fiber and matrix due to different creep characteristics of its constituents.

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Perspectives on the Use of Robots in Etho-experimental Approaches to Animal Behavior (심리학 및 행동생물학적 연구에서 동물 로봇의 활용과 전망)

  • Choi, June-Seek
    • The Journal of Korea Robotics Society
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    • v.17 no.1
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    • pp.86-92
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    • 2022
  • Utilization of small robots in psychology and biology provides a new breakthrough in understanding the neurobiological mechanisms of various animal behavior. The expansion of robot use in animal research is partly due to increased availability of economically plausible mobile robots and also due to the current shift in animal research toward more ecologically valid experiments. Ground-breaking experimental findings are expected when the behavioral variables are manipulated in more natural situations. In addition, the results from laboratory could be generalized more easily with added ecological validity. The current paper attempts to review a wide range of applications of animal robots used to study animal behavior and to highlight major advantages and limitations. In particular, this review focuses more on the psychological impact of animal robots than engineering details about their structure and operation. Finally, this review will provide some practical considerations when employing robots in animal experiments.

Transient Response of Magnetic Field Integral Equation Using Laguerre Polynomials as Temporal Expansion Functions (라겐르 함수를 시간영역 전개함수로 이용한 자장 적분방정식의 과도 응답)

  • 정백호;정용식
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.52 no.4
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    • pp.185-191
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    • 2003
  • In this Paper, we propose an accurate and stable solution of the transient electromagnetic response from three-dimensional arbitrarily shaped conducting objects by using a time domain magnetic field integral equation. This method does not utilize the conventional marching-on in time (MOT) solution. Instead we solve the time domain integral equation by expressing the transient behavior of the induced current in terms of temporal expansion functions with decaying exponential functions and Laguerre·polynomials. Since these temporal expansion functions converge to zero as time progresses, the transient response of the induced current does not have a late time oscillation and converges to zero unconditionally. To show the validity of the proposed method, we solve a time domain magnetic field integral equation for three closed conducting objects and compare the results of Mie solution and the inverse discrete Fourier transform (IDFT) of the solution obtained in the frequency domain.

Analysis of Temperature dependent Thermal Expansion Behavior in MMCs for Electronic packaging (전자 패키징용 금속복합재료의 온도에 따른 열팽창 특성)

  • 정성욱;남현욱;정창규;한경섭
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2002.05a
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    • pp.73-76
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    • 2002
  • This study developed SiC/Al composites for electronic packaging to which reinforcements were added with the volume fractions of 49%, 56% and 63% by the squeeze casting method. 0.8 wt.% of the inorganic binder as well as the $Al_2O_3$ fiber and SiC particles with the volume fraction of 1:10 were added to the SiC/Al composites For the produced SiC/Al composites, the CTEs (coefficients of thermal expansion) were measured from 30 to $300^{\circ}C$ and compared with the FEM numerical simulation to analyze the temperature dependent properties. The experiment showed the CTEs of SiC/Al composites that were intermediate values of those of Rule of Mixture and Turner's Model. The CTEs were close to Turner's Model in the room temperature and approached the Rule of Mixture as the temperature increases. These properties analyzed from the difference of the average stress acting between the matrix and the reinforcements proposed in this study

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