• 소성∙가공
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• 제10권5호
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• pp.383-388
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• 2001

In describing the plastic deformation behaviour of ultrafine-grained materials, a phase mixture model in which a polycrystalline material is regarded as a mixture of a crystalline phase and a grain boundary phase has been successful. The deformation mechanism for the grain boundary phase, which is necessary for applying the phase mixture model to polycrystalline materials, is modelled as a diffusional flow of matter along the grain boundary. A constitutive equation for the boundary diffusion creep of the boundary phase was proposed, in which the strain rate is proportional to (stress/grain siz $e^{2}$). The upper limit of the stress of the boundary phase was set to equal to the strength to the amorphous phase. The proposed model can explain the strain rate and grain size dependence of the strength of the grain boundary phase. Successful applications of the model compared with published experimental data are described.

• Earthquakes and Structures
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• 제18권3호
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• pp.379-390
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• 2020

Four full-scaled partially confined and unconfined masonry panels were tested with monotonic lateral loads. To study the effects of vertical force and boundary columns, two specimens with no boundary columns were subjected to different vertical forces, while two wing-wall specimens had the column placed eccentrically and in the middle, respectively. The specimens with no boundary columns exhibited ductile rocking behavior, where the lateral strength increased with increasing vertical compression. The wing-wall specimens with columns behaved as strut-and-tie systems. The column-panel interaction resulted in greater strength, lower deformation capacity and differences in failure modes. A comparison with analytical models showed that rocking strength can be accurately estimated using vertical force and the panel aspect ratio for panels with no boundary columns. The estimation for lateral strength on the basis of a panel section area indicated scattered error for wing-wall specimens.

• 한국세라믹학회지
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• 제29권10호
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• pp.806-814
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• 1992

The aim of this study was to investigate the change in compressive strength, freacture behavior and degradation of piezoelectric properties with compressive cyclic loading in Pb(Zr, Ti)O3 of tetragonal, morphotropic phase boundary and rhombohedral composition. The highest compressive strength was found in rhombohedral composition. After poling treatment the strength increased by 8.4% and 6.5% in tetragonal and morphotropic phase boundary compositions respectively while changed little in rhombohedral. The increase of compressive strength after poling treatment is believed to be due to the internal stress around grain boundary by domain alginment toward electric field direction in the microstructures having tetragonality and the occurrence of domain switching to the direction perpendicular to electrical field during fracture. Fracture mode relatively change from transgranular to intergranular was observed in the large grain sized tetragonal and morphotropic phase boundary compositions before and after poling but the transgranular fracture mode always remained in the rhombohedral composition. From the X-ray diffractometer analysis the domains parallel to the electric field direction is known to undergo rearrangement during the cyclic loading into random direction that is responsible for the degradation of piezoelectric property.

• 디지털융복합연구
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• 제11권1호
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• pp.191-198
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• 2013

최근 스마트폰, 태블릿PC, 와이브로(WiBro), LTE 등 정보기술의 발전과 함께 스마트워크에 대한 관심이 증대되고 있다. 본 연구에서는 스마트워크를 도입함으로써 나타나는 업무 비업무 경계 모호성의 근본 문제를 경계 이론에 통해 이해하고자 하였다. 국내 K사의 재택근무와 스마트워크센터근무 이용자를 대상으로 경계 이론에서 제시하는 핵심 개념인 침투가능성, 경계 강도, 간섭 등을 포괄적으로 고려한 실증 연구를 수행하였다. 연구 결과를 통해 스마트워크 이용자는 업무와 비업무 영역 간의 비대칭성을 지각하고 있다는 사실을 확인하였다. 본 연구는 스마트워크와 관련된 향후 연구에서 업무와 비업무 영역 간 양방향성을 전제하여 경계 관리 전략을 고려할 필요성을 제시하고 있다.

• Journal of Pharmaceutical Investigation
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• 제31권1호
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• pp.13-18
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• 2001

This study was to investigate the relationship between the gel layer thickness and swelling boundary via strength measurements using texture analysis. The novel texture analysis approach was used to examine the dynamics of swelling behavior in a ternary polymeric matrix tablet. The method permitted the characterization of the changes occurring at the peripheral as well as within interior boundary of the swelling during water ingress. The increase in gel strength for pectin, HPMC, and a ternary mixture with gelatin was found to depend on polymer concentration. Therefore, this method is further applicable to characterize the swelling behavior and provide opportunity to differentiate the gel-layer from that of swelling boundary.

• 한국세라믹학회지
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• 제33권1호
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• pp.49-55
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• 1996

The aim of this study is to investigate the change of bending strength and fatigue strength in the unpoled and poled Pb(Zr, Ti)O3 ferroelectrics of tetragonal morphotropic phase boundary (MPM) and rhombohedral com-position in terms of internal stress which is measured by XRD method. Before poling treatment the highest bending strength was found in rhombohedral composition. After poling treatment the bending strength decreas-ed in all compositions but it decreased most remarkably in tetragonal composition. The most prominent de-crease of bending strength after poling treatment in tetragonal was attributed to the occurrence of microcracks due to highanisotropic internal stress around grain boundary which was induced of bending strength after poling in MPB and rhombohedral composition was not due to the occurrence of microcracks but to the increase in tensile internal stress perpendicular to the direction of crack propagation by domain alignment. Fatigue strength was higher before poling treatment than after poling treatment for various compositions.

• 열처리공학회지
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• 제16권4호
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• pp.197-204
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• 2003

Honeycomb structure has been fabricated by brazing method using 0.1 wt%C and 1.0wt%C carbon steel core and STS304 stainless steel face sheet. Core shear strength ratio in W and L directions was 1:1.03 in 7 mm cell size, whereas 1:1.45 in 4 mm cell size. Flexural strength on face sheet was 166.4 MPa (0.1 wt%C, W direction), 171.1 MPa (0.1 wt%C, L direction), and 120.2 MPa (1.0 wt%C, W direction) in 7 mm cell size. And in 4mm cell size specimen, it was 169.2 MPa (0.1 wt%C, W direction), 224.2 MPa (0.1 wt%C, L direction). This means that flexural strength of 0.1 wt%C core material was higher than that of 1.0wt%C core material, which was contrary to expectation. SEM and EDS analysis represented that grain boundary diffusion had occurred in0.1 wt%C core, but no grain boundary diffusion in 1.0 wt%C core. And corrugated surface of 0.1 wt%C core was flat, whereas that of 1.0 wt%C core was not flat. As a result, contact area between two 1.0 wt%C cores was much less than that of 0.1 wt% cores, It is thought to be main reason for lower flexural strength of 1.0 wt%C core.

• 한국환경복원기술학회지
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• 제4권3호
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• pp.49-54
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• 2001

It is common that the soil layer is a few meters below the earth's surface and the rock mass is below the soil layer in the view of geological characteristics in Korea. And the boundary between rock and soil is clearly divided. When dealing with the stability of rock masses, as in the case of rock slopes or dam foundations, the majority of the collapses is not within the soil layer, but within the soil-rock boundary. Therefore it is important to identify the shear strength characteristics between soil-rock boundary. And then in the method of reinforcement on landslide this chose a cut slope near Daemo elementary school in Seoul, surveyed shear strength between soil-rock contacts and considered a large scale collapse using a limit equilibrium method.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.192-195
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• 2000

In describing the plastic deformation behaviour of fine grained materials a phase mixture model in which a polycrystalline material is regarded as a mixture of a crystalline phase and a grain boundary phase has been successful. The deformation mechanism for the grain boundary phase which is necessary for applying the phase mixture model is modelled as a diffusional flow of matter though the grain boundary. The proposed model can explain the strain rate and grain size dependence of the strength of the grain boundary phase.

• 대한기계학회논문집B
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• 제24권5호
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• pp.733-743
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• 2000

We solve the integral representation of the Navier-Stokes equations in a lagrangian view by tracking the particles, which have vortex strengths. We simulate the unsteady viscous flow around an impulsively started cylinder using the vortex particle method. Particles are advanced via the Biot-Savart law for a lagrangian evolution of particles. The particle strength is modified based on the scheme of particle strength exchange. The solid boundary satisfies the no-slip boundary condition by the vorticity generation algorithm. We newly modify the diffusion scheme and the boundary condition for simulating an unsteady flow efficiently. To save the computation time, we propose the mixed scheme of particle strength exchange and core expansion. We also use a lot of panels to ignore the curvature of the cylinder, and not to solve the evaluation of the surface density. Results are compared to those from other theoretical and experimental works.