• Title/Summary/Keyword: Micro-mechanics

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UNIFICATION OF THERMO-PHYSICS OF MATERIALS AND MECHANICS OF STRUCTURES - TOWARD A LIFE SPAN SIMULATOR OF STRUCTURAL CONCRETE -

  • Maekawa, K.;Ishida, T.
    • Proceedings of the Korea Concrete Institute Conference
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    • 1999.10a
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    • pp.29-46
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    • 1999
  • The performance based design obligates quantitative assessment of required performances by means of transparent and objective science. In this design scheme, simulation of both macro and micro-scale structural behaviors is thought to be a powerful tool. This paper proposes a way how to unify the structural safety and serviceability check method and durability assessment of RC structures. Though component chemical-physical processes are crudely assumed, system dynamics of micro-scale pore structure formation and macro-scale defects and deformation of structures was shown as possible and promising approach in future. The authors understand that the unification of structural and durability design has just started. For further progress and development, predictive tool of structural behaviors from birth to death of concrete under any specified environment and load serves as an essential technicality.

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Estimation of Micro-discontinuity Distribution Using Scanline Survey in Granites (조사선을 이용한 화강암의 미세 불연속면 분포성상 평가)

  • 이상은;조상호;양형식;박홍민
    • Tunnel and Underground Space
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    • v.9 no.4
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    • pp.364-372
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    • 1999
  • In this paper, mechanical characteristics of micro-defects in granitic rock was studied. Crack spacing and length were investigated by scanline survey in specimen of granite. To estimate the direction and distribution of potential microcrack in granite, thin sections were made for three direction of Rift, Grain and Hardway axis of the rock specimen. The density and length of microcrack were investigated quantitatively. Three directions of microcracks are comparatively perpendicular. Crack density varies as direction differs, but crack length doesn't show influence of direction.

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A Study on Analysis for Bulk Forming of a Single Crystal Milli-Product (단결정 밀리 부품의 입체성형 해석에 관한 연구)

  • Lee Y. S.;Kim Y. I.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2001.05a
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    • pp.245-249
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    • 2001
  • This paper is concerned with numerical analyses for bulk forming of a single crystal milli-product, whose typical size ranges from a few hundreds ${\mu}m$ to a few mm. The numerical formulation invoked in this paper combines the crystal plasticity theory considering texture development and the ductile damage mechanics for growth of micro voids, since orientation development and growth of micro voids become the primary factors for bulk forming of milli-size products. As applications, milli-extrusion of a single crystal round bar and milli-rolling of a single crystal plate are simulated and the results are discussed in detail.

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A composite crack model for concrete based on meshless method

  • Lu, Xin-Zheng;Jiang, Jian-Jing;Ye, Lie-Ping
    • Structural Engineering and Mechanics
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    • v.23 no.3
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    • pp.217-232
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    • 2006
  • A crack model for the fracture in concrete based on meshless method is proposed in this paper. The cracks in concrete are classified into micro-cracks or macro-cracks respectively according to their widths, and different numerical approaches are adopted for them. The micro-cracks are represented with smeared crack approach whilst the macro-cracks are represented with discrete cracks that are made up with additional nodes and boundaries. The widely used meshless method, Element-free Galerkin method, is adopted instead of finite element method to model the concrete, so that the discrete crack approach is easier to be implemented with the convenience of arranging node distribution in the meshless method. Rotating-Crack-Model is proved to be preferred over Fixed-Crack-Model for the smeared cracks of this composite crack model due to its better performance on mesh bias. Numerical examples show that this composite crack model can take advantage of the positive characteristics in the smeared and discrete approaches, and overcome some of their disadvantages.

Effective mechanical properties of micro/nano-scale porous materials considering surface effects

  • Jeong, Joonho;Cho, Maenghyo;Choi, Jinbok
    • Interaction and multiscale mechanics
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    • v.4 no.2
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    • pp.107-122
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    • 2011
  • Mechanical behavior in nano-sized structures differs from those in macro sized structures due to surface effect. As the ratio of surface to volume increases, surface effect is not negligible and causes size-dependent mechanical behavior. In order to identify this size effect, atomistic simulations are required; however, it has many limitations because too much computational resource and time are needed. To overcome the restrictions of the atomistic simulations and graft the well-established continuum theories, the continuum model considering surface effect, which is based on the bridging technique between atomistic and continuum simulations, is introduced. Because it reflects the size effect, it is possible to carry out a variety of analysis which is intractable in the atomistic simulations. As a part of the application examples, the homogenization method is applied to micro/nano thin films with porosity and the homogenized elastic coefficients of the nano scale thickness porous films are computed in this paper.

Finite Element Analysis for Extrusion/Drawing of Milli-Size Bar (밀리봉의 압출/인발의 유한요소해석)

  • Kim Y. I.;Lee Y. S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2000.10a
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    • pp.70-73
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    • 2000
  • A finite element analysis model is suggested for analysis of forming process of milli structure whose size is from a few hundreds ${\mu}m$ to a few mm. In this paper, finite element formulation which assemble crystal plasticity theory considering texture development with damage mechanics is developed, since orientation development and growth of micro voids became the primary factors for deformation aspects in large deformation of milli structure. Applying to, extremely, extrusion process of single crystal and extrusion/drawing process of polycrystal milli-size bar, extrusion force, preferred orientation, and damage evolution are examined to understand the characteristics of deformation of milii-size bar.

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Tension Properties of Engineered Cementitious Composite(ECC) (고기능성 시멘트계 복합재료의 인장 특성에 대한 연구)

  • 김동완;경민수;배병원;전경숙;임윤묵;김장호
    • Proceedings of the Korea Concrete Institute Conference
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    • 2003.11a
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    • pp.244-247
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    • 2003
  • Recently, construction materials have been quickly advancing. Especially, the rate of development of cement based construction materials is much quicker than steel or composite materials. In order to optimize the ductility and strength of cement based materials, Micro-Mechanics based fiber concrete called Engineered Cement Composite (ECC) has been developed and studied extensively by many researchers in the field due to ECC's remarkable flexural strain and strength capacities, many leading nation (i.e., US, Japan and European countries have reached the point of being able to use ECC in actual constructions. But, due to the belated interest in the field, Korea is lagging behind the leading countries. ECC's ability to use its short fibers to bridge micro-cracks (50-80㎛ in width) allows great ductility and strength. In this study, it is confirmed excellency of ECC through the test of tensile strength.

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A Numerical Prediction of the Forming Limit Diagram Considering Damage Evolution (결함 성장을 고려한 수치해석적 성형한계도 예측)

  • Kim, K.T.;Song, J.H.;Lee, G.A.;Lee, H.W.;Kim, S.H.;Lee, Y.S.
    • Transactions of Materials Processing
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    • v.18 no.8
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    • pp.596-600
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    • 2009
  • Finite element simulation is an alternative method to practically find the forming limit diagram(FLD). In this paper, the novel fracture criterion is utilized to predict the FLD in conjunction with finite element analysis for sheet forming. The principal scheme of the fracture criterion in this paper is that growth of the micro voids leads up to fracture in the viewpoint of micro-mechanics. The numerical FLD is verified by results of the out-of plane stretching test using hemispherical punch. The verification is also conducted about two types of material. These results are in good accord with the experimental results. Especially, the proposed scheme is appropriate to predict FLDs for a restricted material with low ductility after the instability point or ultimate tensile strength.

Behavior of Engineered Cementitious Composite(ECC) Flexural Members Based on Mix Proportions and Curing Conditions (고기능성 시멘트계 복합재료 배합비 및 양생조건에 따른 휨부재의 거동)

  • 경민수;김동완;배병원;전경숙;임윤묵;김장호
    • Proceedings of the Korea Concrete Institute Conference
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    • 2003.05a
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    • pp.361-366
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    • 2003
  • Recently, construction materials have been guickly advancing. Especially, the rate of development of cement based construction materials is much quicker than steel or composite materials. In order to optimize the ductility and strength of cement based materials, Micro-Mechanics based fiber concrete called Engineered Cement Composite (ECC) has been developed and studied extensively by many researchers in the field due to ECC's remarkable flexural strain and strength capacities, many leading nation (i.e., US, Japan and European countries have reached the point of being able to use ECC in actual constructions. But, due to the belated interest in the field, Korea is lagging behind the leading countries. ECC's ability to use its short fibers to bridge micro-cracks (50-80㎛ in width) allows great ductility and strength. ,In this study, ECC with superior material capacities are manufactured using domestic materials such as cement, silica sand, metal cellulose, etc. Using only domestic products, the optimal W/C ratio and mixing procedures are determined.

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Nanohole Fabrication using FIB, EB and AFM for Biomedical Applications

  • Zhou, Jack;Yang, Guoliang
    • International Journal of Precision Engineering and Manufacturing
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    • v.7 no.4
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    • pp.18-22
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    • 2006
  • Although many efforts have been made in making nanometer-sized holes, there is still a major challenge in fabricating individual single-digit nanometer holes in a more controllable way for different materials, size distribution and hole shapes. In this paper we describe our efforts to use a top down approach in nanofabrication method to make single-digit nanoholes. There are three major steps towards the fabrication of a single-digit nanohole. 1) Preparing the freestanding thin film by epitaxial deposition and electrochemical etching. 2) Making sub-micro holes ($0.2{\mu}\;to\;0.02{\mu}$) by focused ion beam (FIB), electron beam (EB), atomic force microscope (AFM), and others methods. 3) Reducing the hole size to less than 10 nm by epitaxial deposition, FIB or EB induced deposition and micro coating. Preliminary work has been done on thin films (30 nm in thickness) preparation, sub-micron hole fabrication, and E-beam induced deposition. The results are very promising.