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Recent Development of Science and Technology of Hard Materials in Japan

  • Hayashi, Koji
    • Journal of Powder Materials
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    • v.5 no.4
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    • pp.303-311
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    • 1998
  • Hard materials such as hardmetal, coated hardmetal, cermet, ceramics and diamond or c-BN sintered compact are a kind of grain-dispersed alloy with high volume of hard particles. These are used for cutting tools, wear-resistant tools, rock bits, high pressure apparatus, etc. The annual production in Japan is about 1.7 billion dollars (200 billion yen). This is greatly owed to the development in science and technology which has been accomplished by applying new concepts such as fine or uniform grain microstructure, orientation of crystal grains, functionally graded material, artificial lattice and coherent bonding in recent years. In this review, the development in recent years in Japan is briefly summarized.

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The Mechanical Properties of High Strength Concrete in Massive Structures

  • Park, Ki-Bong
    • Architectural research
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    • v.15 no.1
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    • pp.53-58
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    • 2013
  • High strength concrete is being used increasingly in mass structure projects. The purpose of this study is to investigate the influence of temperature during mixing, placing and curing on the strength development, hydration products and pore structures of high strength concrete in mass structures. The experiments were conducted with two different model walls, viz.: 1.5 m and 0.3 m under typical summer and winter weather conditions. The final part of this study deal with the clarification of the relationship between the long-term strength loss and the microstructure of the high strength concrete at high temperatures. Test results indicated that high elevated temperatures in mass concrete structures significantly accelerate the strength development of concrete at the early ages, while the long-term strength development is decreased. The long-term strength loss is caused by the decomposition of ettringite and increased the total porosity and amount of small pores.

Prediction of compressive strength of slag concrete using a blended cement hydration model

  • Wang, Xiao-Yong;Lee, Han-Seung
    • Computers and Concrete
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    • v.14 no.3
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    • pp.247-262
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    • 2014
  • Partial replacement of Portland cement by slag can reduce the energy consumption and CO2 emission therefore is beneficial to circular economy and sustainable development. Compressive strength is the most important engineering property of concrete. This paper presents a numerical procedure to predict the development of compressive strength of slag blended concrete. This numerical procedure starts with a kinetic hydration model for cement-slag blends by considering the production of calcium hydroxide in cement hydration and its consumption in slag reactions. Reaction degrees of cement slag are obtained as accompanied results from the hydration model. Gel-space ratio of hardening slag blended concrete is determined using reaction degrees of cement and slag, mixing proportions of concrete, and volume stoichiometries of cement hydration and slag reaction. Furthermore, the development of compressive strength is evaluated through Powers' gel-space ratio theory considering the contributions of cement hydration and slag reaction. The proposed model is verified through experimental data on concrete with different water-to-binder ratios and slag substitution ratios.

Friction and Wear Behaviors of WC-Co/WC-Co Pairs in Air

  • Hosokawa, H.;Nakajima, T.;Shimojima, K.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.629-630
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    • 2006
  • To investigate sliding friction and wear behaviors of WC-Co/WC-Co pairs containing different WC grain sizes, the ball-on-disc test in air were carried out, where WC grain sizes a 0.5μm (F.G.) and 1.5μm (C.G.). The wear volume of F.G. pin for F.G. pin/C.G. disc is larger than that of F.G. pin for F.G. pin/F.G. disc due to higher friction coefficient, and the surfaces after wear test are richer in oxygen compared to those before test. Furthermore, the wear debris, which is composed of nona-scale grain, after the wear test are remarkably richer in oxygen than to those before test.

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A study on the improvement of thickness accuracy in a plate mill

  • Lee, Duk-Man
    • 제어로봇시스템학회:학술대회논문집
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    • 2003.10a
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    • pp.723-727
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    • 2003
  • In this paper, two methods are discussed for good rolling force prediction in a plate mill. One is about the development of a long and a short learning scheme using a Neural Network for normal rolling and the other is about a mathematical model improvement by considering microstructural changes for controlled rolling. The research results are implemented in a on-line system of Pohang Works in POSCO and the field tests have showed that the prediction accuracies of rolling force are highly improved.

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Development of Centrifugal Forming Process for HTS Tube Fabrication (고온초전도체 튜브 제조를 위한 원섬 성형 공정 개발)

  • 정승호;장건익
    • Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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    • 2002.02a
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    • pp.98-100
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    • 2002
  • We developed the Centrifugal Forming Process(CFP) for HTS tube fabrication. The self-designed equipment for CFP is devided into 3 main parts depending on its role and functions. the melting part by heating of high inductive frequency, centrifugal forming part for the tube and efficient microstructure control of Bi2212 phase and molding part for tube detachment after heat treatment. In this paper we will introduce self designed Centrifugal Forming Process for HTS tube fabrication and discuss about the results related mold materials in terms of high Tc superconductor.

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Filler-Polymer Interactions in Filled Styrene-Butadiene Rubber Compounds

  • Park, Sung-Seen
    • Macromolecular Research
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    • v.9 no.1
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    • pp.45-50
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    • 2001
  • Formation of bound rubber depends on the filler-polymer interactions including physical adsorption, chemisorption, and mechanical interaction. Bound rubbers consist of tightly and loosely bound ones. Styrene-butadiene rubber (SBR) is composed of styrene, 1,2-, cis-1,4-, and trans-1,4-units. Filler-polymer interactions of each components of SBR with fillers, carbon black and silica, were studied by analysis of microstructure of the bound rubber. Filler-polymer interaction of the 1,2-unit with the fillers was found to be stronger than those of the other components and this phenomenon was shown more clearly in the tightly bound rubber.

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Development of Bevel Gear by Powder Forging Process (분말단조에 의한 베벨기어의 성형 기술 연구)

  • 이정만
    • Journal of Powder Materials
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    • v.4 no.4
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    • pp.258-267
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    • 1997
  • The powder forging process is an attractive manufacturing route for bevel gears. It offers beneficial material utilization and the minimization of finishing operations over that of conventional hot forging. The paper describes the process conditions for the powder forging of bevel gear, for example, powder alloy design, preform design, deformation of sintered preform, forging processes. The characteristics of prototype gear are investigated with microstructure, the density distribution, surface roughness of tooth, bending strength test of tooth, etc. The results of the bending strength test may prove the mechanical properties of powder forged gear.

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