• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.824-825
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• 2006

Homogeneous microstructures of the PM compacts are difficult to attain when mixed elemental powders are used. This study examined the microstructures of pressed-and-sintered and MIM products that contain Ni and Mo.Ni-rich areas, which were lean in carbon and were soft and were found easily in regular specimens. Gaps or cracks near the Ni-rich or Mo-rich areas were also frequently observed. This problem worsened when Ni and Mo particles were large and were irregular in shape. By using ball milling treatment and ferroalloy powders, the microstructure homogeneity and mechanical properties were improved. The addition of 0.5wt%Cr further improved the distribution of Ni because Cr reduced the repulsion effect between nickel and carbon. With the elimination of Ni-rich areas, more bainites and martensites were formed and mechanical properties were significantly improved.

• Smart Media Journal
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• v.5 no.2
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• pp.24-32
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• 2016

Recently, the development of electronic teaching materials and the demand of digital learners have led the needs on the education contents that replace learning from character information and the change of an information design method for this. Chinese character education in the traditional schooling mainly focuses on writing and memorization (semantic memory). This way that the stories do not exist has brought the learners' recognition that Chinese character is difficult to learn. Meanwhile, for a language study such as English, cross-media development between printed materials and audio-visual materials has been actively introduced. The method that extends episode memories along with memorization through a story is widely used. Therefore, this content suggests a prototype, which is broken away from an existing way of learning Chinese character that mainly focuses on writing, one sided instruction and information cramming. This makes learners learn through a story from printed materials and animation. Furthermore, it suggests a method that extends episode memories through Chinese education contents based on IoT explaining the principle of Chinese character by combining IT technology (information and communications, IoT) and education contents on block toys.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.75-80
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• 2012

Helmholtz resonator is widely used acoustic instrument which has high absorption characteristics at its resonance frequency. Particularly it maintains good performance even in the low frequency region that is difficult to control by general porous absorptive materials. However, under severely high sound pressure level, the absorption characteristics are changed by increase of resistance due to nonlinear behavior of neck impedance. Because of this nonlinear behavior, it is difficult to obtain the expected absorption performance under high sound pressure environment. Thus, in order to prevent excessive rise of resistance, the resonator with neck having cross section dimension decrease away from the entry of the resonator cavity could be suggested. This paper introduces the experiment method and results about nonlinear characteristics of Helmholtz resonator with tapered neck and proposes the approximate nonlinear impedance model.

• Journal of Welding and Joining
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• v.33 no.5
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• pp.20-25
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• 2015

Clad steel has good corrosion resistance and mechanical properties arising from the hot rolling of dissimilar metals, such as carbon steel and stainless steel. However both good corrosion resistance from the cladding plate material(stainless steel) and mechanical properties from the base plate material (carbon steel) are difficult to obtain because the different steels display opposite behaviors during the cladding process. In order to make clad steel for application in the hulls of ships, proper materials selection and heat-treatment conditions are necessary. In this study, mechanical properties of base plate materials with different chemical composition were evaluated according to heat condition of cladding plate material.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.545-550
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• 2002

Concrete is one of the essential structural materials in the construction. But, concrete consists of many materials and is affected by many factors such as properties of materials, site environmental situations, and skill of constructor. Therefore, concrete mixes depend on experiences of experts. However, it is more and more difficult to determine concrete mixes design by empirical means because more ingredients like mineral and chemical admixtures are included. Artificial Neural Networks(ANN) are a mimic models of human brain to solve a complex nonlinear problem. They are powerful pattern recognizers and classifiers, also their computing abilities have been proven in the fields of prediction, estimation and pattern recognition. Here, among them, the back propagation network and radial basis function network are used. Compositions of high-performance concrete mixes are eight components(water, cement, fine aggregate, coarse aggregate, fly ash, silica fume, superplasticizer and air-entrainer). Compressive strength and slump are measured. The results show that neural networks are proper tools to minimize the uncertainties of the design of concrete mixtures.

• Ceramist
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• v.23 no.1
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• pp.4-15
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• 2020

The recent advances and popularity of 3D printing technology have centered around building polymerbased 'plastic' materials, due to their low cost, simple and efficient processing, and mechanical toughness. For this reason, printable polymers are actively recruited to create 'ceramic resins' that allow more facile fabrication of ceramic materials that are difficult to print directly. Herein, a brief history and the current state of ceramic 3D printing technology aided by polymer is summarized. In addition, a new ceramic 3D printing technology using polymer-derived ceramics (PDC) is also introduced.

• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.392-398
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• 1990

To improve free-cutting property, fine Pb, Bi particles is necessary to be distributed evenly in Al-Cu alloy. The control of added element size and distribution are very difficult because of the physical properties of Pb, Bi. The effect of master alloy compositions on microstructure and particle distribution was investigated. The ribbon shape of Pb-50wt% Bi master alloy showed the best results. And Ti addition improved even distribution of Pb, Bi particles. Particles grown from $L_2$ phase were considered to be the Pb, Bi compound.

• Proceedings of the Korean Vacuum Society Conference
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• 1998.02a
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• pp.105-106
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• 1998

Evaluation of def3ects by etch-ppit formation was studied. A NaOH(30 mol%) etchant was found useful for etch-ppit developpment on ZnSe-based eppilayers grown on (001) gaAs. And a H3ppO4(85 mol%) was used in order to developp etch-ppits on GaN-base eppilayers grown on (0001) Al2O3 After etch-ppit formation on the surfsce. Transmission Electron Microscoppy(TEM) was cppmdicted. By etch-ppit developpment and TEM observation we could determine the defect typpes by etch-ppit configurfations and found origin of etch-ppit in the cse of ZnSe-based materials. Based uppon these results we can do defect identification by etch-ppit test simpply. In the case of GaN-based materials we could evaluate nanoppippe density. however high density of threading dislocations in GaN eppilayers were not revealed by etch-ppit developpment. Based uppon these results we can evaluate the nanoppippe density which difficult to evaluate using TEM beacause of its small size(diameter). And at ppresent status direct matching of etch-ppit density to dislocation density would make severe mistake.

• International Journal of Aerospace System Engineering
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• v.3 no.1
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• pp.1-4
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• 2016

Functionally graded materials (FGMs) are becoming very popular in various industries due to their effectiveness of the utilization of their constituent elements. However, the modelling of these materials is difficult due to the complex nature of variation of material properties across the thickness. Many shear deformation theories have been developed and employed for the analysis of such functionally graded plates (FGPs). A recently developed inverse hyperbolic shear deformation theory has been successfully employed by Grover et al. [1] for the analysis of laminated composites and sandwich plates. The objective of the study is to obtain finite element solution for the structural analysis of functionally graded plates using inverse hyperbolic shear deformation theory. Finite element analysis facilitates the analysis of complex problems such as functionally graded plates with different boundary conditions and different loadings.

• Journal of the Korean Society of Safety
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• v.10 no.3
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• pp.3-10
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• 1995

For most engineering materials are influenced by the dominant mechanism resisting crack extention under large scale yielding conditions. Continuum mechanics analysis shows that fracture toughness, in addition to depending on young's modulus, flow stress strain hardening exponent, and yield strain, should be nearly proportoinal to the effective fracture ductility obtained for the stress state characteristic for region ahead of the crack; plane stress or plane strain. It's known that, in most ductile materials, crack propagation of the material strongly governed by the $J_{IC}$ value, which is still difficult to determine for it's complicate and treble-some determinative process. This paper, on the assumption that, initiation of crack tip strain field reaches on the relationships between the critical value of J-integral ($J_{IC}$) and the local fracture strain(${\varepsilon}_c$) in uniaxial tensile test in the region of maximun reduction areas was described.