• Title/Summary/Keyword: grain size trend

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Modelling the Tensile Instability of Nanocrystalline Metallic Materials (나노금속재료의 인장불안정에 대한 모델링)

  • Kim H. S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.10a
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    • pp.251-254
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    • 2001
  • In this paper, the effect of grain refinement on room temperature ductility of copper was addressed. Recent experimental results have shown that this material, as well as a number of other single-phase metals that are ductile when coarse-grained, loose their ductility with decreasing grain size in the sub micrometer range. A recently developed model in which such materials are considered as effectively two-phase ones (with the grain boundaries treated as a linearly viscous second phase) was applied to analyze stability of Cu against ductile necking. As a basis, Hart's stability analysis that accounts for strain rate sensitivity effects was used. The results confirm the observed trend for reduction of ductility with decreasing grain size. The model can be applied to predicting the grain size dependence of ductility of other metallic materials as well.

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Effects of Atmospheric Powder and Grain Size on Electrical Properties of Lanthanum-modified $PbTiO_3$ Ceramics

  • Byung Sung kang;You, Dong-Joo;Park, Si-Kyung
    • The Korean Journal of Ceramics
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    • v.6 no.4
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    • pp.396-400
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    • 2000
  • Dielectric and piezoelectric properties of Pb$_0.9$La$_0.1$TiO$_3$ ceramics were investigated as a function of grain size. Sintering atmosphere was controlled with changing the kind of atmospheric powder and its amount. It was confirmed that dielectric and piezoelectric of Pb$_0.9$La$_0.1$TiO$_3$ were strongly influenced by the sintering atmosphere. Relative dielectric constant of Pb$_0.9$La$_0.1$TiO$_3$ which was sintered in PbO-deficient atmosphere made by Pb$_0.9$La$_0.1$TiO$_3$ powder, increased with the grain size. However, the dielectric constant of the samples sintered in the PbO-sufficient atmosphere made by PbZrO$_3$ powder was slightly decreased with the grain size. Piezoelectric d$_33$ constant of Pb$_0.9$La$_0.1$TiO$_3$ also showed a different trend, depending on the sintering atmosphere. It was almost constant in the range of grain size of 1.3~2.3 $\mu$m when the samples were sintered in the PbO-sufficient atmosphere, while it intensively decreased with the grain size in the case of the PbO-deficient condition.

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Morphological and Textural Characteristics of the Beach-dune System in South Korea, with the Possibility of a Dune Type Scheme Based on Grain-size Trend (국내 해안의 해빈-해안사구 지형 및 퇴적물 특성과 입도기반 사구유형 분석)

  • Rhew, Hosahng;Kang, Jihyun
    • Journal of The Geomorphological Association of Korea
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    • v.27 no.3
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    • pp.53-73
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    • 2020
  • Morphology and grain size distribution of coastal dunes should be well documented because they are critical to dune's buffering capacity and resilience against storm surges. The nationwide coastal dune survey produced the dataset, including beach-dune topographic profiles and grain size parameters for frontal beaches, foredunes, and inland dunes. This research investigated the dataset to describe geomorphic and textural properties of coastal dunes: foredune slopes, dune heights above approximately highest high water, mean size, and sorting, together with associated variables of coastal setting that influence coastal dunes. It also explores the possibility of a dune type scheme based on gran size trends. The results are as follows. First, the coast in which dunes are developed is the primary control on foredune morphology and sediment texture. Coastal dunes on the east coast were developed more alongshore rather than inland, with gentler slopes on the higher ground and out of coarser sand. The shore aspect contributes to this pattern because the east coast cannot benefit from prevailing northwesterly. Second, grain size trends from beaches through foredunes to inland dunes were little identified. Third, 12 dune types were identified from 69 dunes, showing the indicative capability for the status of beaches and dunes. We confirmed that the dataset could increase our understanding of the overall characteristics of coastal dune morphology and texture, though there is something to be improved, for example, establishing the refined and comprehensive field survey protocol.

FE Analysis and Experiments of Milli-fart forming Using Grain and Grain Boundary Element (입자요소를 이용한 미세 성형 부품의 유한요소 해석 및 실험)

  • Ku, Tae-Wan;Kang, Beom-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.1
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    • pp.109-118
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    • 2003
  • The recent trend towards miniaturization causes an increased demand for parts with very small dimensions. Milli-structure components are classified as a component group whose size is between macro- and micro-scale. The manufacturing process of these components of thin sheet metal forming has a microscopic properties in addition to a typical phenomenon of bulk deformation because of the forming size. Also, the material properties and the deformation behavior change with miniaturization, which means that, a coarse grained materials show a higher resistance against deformation, when the grain size is in the range of the sheet thickness. In this study, a new numerical approach is proposed to simulate intergranular milli-structure in forming by the finite element method. The grain element and grain boundary element are introduced to simulate the milli-structure in the bending. The grain element is used to analyze the deformation of individual grain while the grain boundary element is for the investigation on the movement of the grain boundary. Also, the result of the finite element analysis is confirmed by a series of milli-sized forming experiments.

Finite Element Analysis and Experiments of Milli-Part Forming of Strip Bending Using Grain Element (입자요소계를 이용한 유한요소 해석)

  • Ku T.W.;Kim D.J.;Kang B.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2002.02a
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    • pp.266-273
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    • 2002
  • Milli-structure components are classified as a component group whose size is between macro and micro scales, that is, about less than 20mm and larger than 1mm. The bending of these components of thin sheets has a typical phenomenon of bulk deformation because of the forming size. The recent trend towards miniaturization causes an increased demand for parts with very small dimensions. The conceptual miniature bending process enables the production of such parts with high productivity and accuracy. The stress values of the flow curve decrease with miniaturization, which means that coarse grained materials show a higher resistance against deformation, when the grain size is in the range of the sheet thickness. In this paper, a new numerical approach is proposed to simulate intergranular milli-structure in forming by the finite element method. The grain element and grain boundary element are introduced to simulate the milli-structure of strip in the bending. The grain element is used to analyze the deformation of individual grain while the grain boundary element is for the investigation on the movement of the grain boundary. Also, the result of the finite element analysis is confirmed by a series of milli-sized forming experiments.

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Modelling Strength and Ductility of Nanocrystalline Metallic Materials

  • Kim, Hyoung-Seop
    • Journal of Powder Materials
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    • v.8 no.3
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    • pp.168-173
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    • 2001
  • The effect of grain refinement of the strength and ductility of metallic materials is investigated. A model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanism. Deformation of the grain interior phase is assumed to be carried by two concurrent mechanisms: dislocation glide and mass transfer by diffusion. The model was exemplified by simulating uniaxial tensile deformation of Cu down to the nanometer grain size. The results confirm the observed strain hardening behaviour and a trend for reduction of ductility with decreasing grain size at room temperature.

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Exploring the Applicability of Grain Size Trend Analysis to Understanding the Morphological Responses of the Deltaic Barrier Islands in the Nakdong River (낙동강 삼각주연안 사주섬의 지형변화에 대한 입도경향 분석의 활용도 탐색)

  • Kim, Sung-Hwan;Rhew, Ho-Sahng
    • Journal of the Korean association of regional geographers
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    • v.13 no.2
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    • pp.119-128
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    • 2007
  • Grain-size trend analysis is the methodology to obtain the net sediment transport pattern from the spatial trends of grain size parameters. It has the potentials to be an effective tool to address the morphological changes of the deltaic barrier islands in the Nakdoog River once we make sure net transport patterns inferred from grain size trend analysis represent the morphological evolution patterns. This research aims to investigate the applicability of the net transport patterns obtained by 'transport vector', proposed by Gao and Collins(1992), to understanding the morphological changes of the Nakdong River deltaic barrier islands. The results indicate that the net transport directions are overall in concordance with the morphological evolution patterns; however, the level of concordance is low in the island with fast growing rate. The reasons may be match or mismatch of temporal scales involved between processes represented by net transport patterns and morphological change analyzed or the rate of morphological change. Consequently, the application of grain size trend analysis in analyzing the morphological changes of deltaic barrier islands requires the careful consideration of temporal scales involved.

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The Effect of Tensile Hold time on the Fatigue Crack Propagation Property and Grain Size on the Creep Behavior in STS 316L. (STS316L의 고온피로균열에 미치는 인장유지시간의 효과 및 결정립크기에 따른 크리프 거동에 관한 연구)

  • 김수영
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2000.04a
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    • pp.373-378
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    • 2000
  • The heat resistant material, in service, may experience static loading, cyclic loading, or a combination of two. An experimental study of crack growth behavior of STS 316L austenitic stainless steel under fatigue, and creep-fatigue loading conditions were carried out on compact tension specimens at various tensile hold times. In the crack growth experiments under hold times. In the crack growth experiments under hold time loading conditions, tensile hold times were ranged from 5 seconds to 100 seconds and its behavior was characterized using the $\Delta$K parameter. The crack growth rates generally increase with increasing hold times. However in this material, the trend of crack growth rates decreases with increasing hold times for short hold time range relatively. It is attributed to a decline in the cyclic crack growth rate as a result of blunting at the crack tip by creep deformation. The effect of grain size on the creep behavior of STS 316L was investigated. Specimens with grain size of 30, 65 and 125${\mu}{\textrm}{m}$ were prepared through various heat treatments and they were tested under various test conditions. The fracture mode of 316L changed from transgranular to intergranular with increasing grain size.

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The Effects of the Distribution Aspect of Precipitate on the Corrosion Behavior of As-Cast Magnesium Alloys

  • 이충도
    • Transactions of Materials Processing
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    • v.8 no.3
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    • pp.295-295
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    • 1999
  • In the present study, the corrosion behavior of AZ91D as-cast alloy was investigated form the viewpoint of the distribution aspect of precipitate ($Mg_{17}Al_{12}$) and the variation of Al concentration in the Mg-rich matrix. The dendrite arm spacing (DAS) of an as-cast specimen was measured as a function of degree which describes the distribution aspect of the precipitate, and the salt spray test was conducted for various grain-sired specimens fur 20 days. The dendrite arm spacing increased as the grain size increased to about 150㎛, but a constant value is indicated when the grain size exceeds that range. Although the relationship between the corrosion rate and grain size is of a nonlinear type, the linear trend between the corrosion rate and the dendrite arm spacing is maintained for the overall range of dendrite arm spacing. Since the precipitate in the as-cast alloy is discontinuously distributed, this linear relationship means that the variation of Al-solute concentration in the Mg-rich matrix has a more potent effect than the protective action of the precipitate on the corrosion behavior of an as-cast alloy.

Poly-Si TFT Technology

  • Noguchi, Takashi;Kim, D.Y.;Kwon, J.Y.;Park, Y.S.
    • Information Display
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    • v.5 no.1
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    • pp.25-30
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    • 2004
  • Poly-Si TFT(Thin Film Transistor) technology are reviewed and discussed. Poly-Si TFTs fabricated on glass using low-temperature process were studied extensively for the application to LCD (Liquid Crystal Display) as well as to OLED(Organic Light Emitting Diode) Display. Currently, one of the application targets of the poly-Si TFT is emphasized on the highly functional SOG(System on Glass). Improvement of device characteristics such as an enhancement of carrier mobility has been studied intensively by enlarging the grain size. Reduction of the voltage and shrinkage of the device size are the trend of AM FPD(Active Matrix Flat Panel Display) as well as of Si LSI, which will arise a peculiar issue of uniformity for the device performance. Some approaches such as nucleation control of the grain seed or lateral grain growth have been tried, so far.