• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.745-751
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• 2011

This study proposes finite element modeling of dislocation punching at cooling after consolidation in order to calculate the strength of particle-reinforced aluminum composites. The Taylor dislocation model combined with strain gradient plasticity around the reinforced particle is adopted to take into account the size-dependency of different volume fractions of the particle. The strain gradients were obtained from the equivalent plastic strain calculated during the cooling of the spherical unit cell, when the dislocation punching due to CTE (Coefficient of Thermal Expansion) mismatch is activated. The enhanced yield stress was observed by including the strain gradients, in an average sense, over the punched zone. The tensile strength of the SiCp/Al 356-T6 composite was predicted through the finite element analysis of an axisymmetric unit cell for various sizes and volume fractions of the particle. The predicted strengths were found to be in good agreement with the experimental data. Further, the particle-size dependency was clearly established.

• Magazine of the Korea Concrete Institute
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• v.16 no.4 s.81
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• pp.70-77
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• 2004

콘크리트 구조물에 대한 많은 기준들의 요건에 따르면, 휨을 받는 철큰 콘크리트(RC) 보의 압축부에서의 응력은 일반적으로 일축의 응력-변형을 관계를 이용하여 계산한다. 이와 같은 접근은 가끔씩 압축력을 받는 콘크리트에서 부서짐이 발성할 때 보의 구조적 거동을 재현하지 못할 수 있다. 결과적으로, RC 구조물의 지지력과 그들의 연성은 근사적으로 평가된다. 본 논문에서는 압축을 받고 있는 콘크리트의 postpeak 거동은 활동면을 이용하여 모델링되었다. 이 활동 면의 모멘트-곡률곡선에서 연화부분에 그 원인이 있다. 제안된 활동현상의 수학적 표현은 압축력을 받는 콘크리트(즉, 연화부분의 거동이 압축영역의 크기와 변형률구배(곡배)에 의존하는)에 있어서 특정한 응력-변형률 관계를 정의하는 것이 얼마나 어려운지를 보여주고 있다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.210-213
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• 2002

The Purpose of this study is to know temperature and thermal stress distribution in specimens during processing of WEDM. If it is constant to the cutting speed and the thickness of material, it is very important to the effect of temperature and the thermal stress distribution after cutting processing. This paper show the analysis result of the distribution of temperature and the residual stress along the direction of thickness before processing of WEDM and after when the cooling temperature is$20^{\circ}C$. The maximum temperature of edge of specimens is $1600^{\circ}C$. It has little temperature gradient in the depth which is 5mm away from edge of specimens. Equivalent residual stress is result in 180.7 MPa at maximum temperature.

• Journal of the Korean Society of Industry Convergence
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• v.9 no.1
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• pp.37-44
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• 2006

Stress and displacement fields of a Mode III crack propagating along the normal to gradient in an orthotropic functionally gradient materials (OFGM), which has (1) an exponential variation of shear modulus and density, and (2) linear variation of shear modulus with a constant density, are derived. The equations of motion in OFGM are developed and solution to the displacement and stress fields for a propagating crack at constant speed though an asymptotic analysis. The first three terms in expansion of stress and displacement are derived to explicitly bring out the influence of nonhomogeneity. When the FGM constant ${\zeta}$ is zero or $r{\rightarrow}0$, the fields for OFGM are almost same as the those for homogeneous orthotropic material. Using the stress components, the effects of nonhomogeneity on stress components are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.9
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• pp.1753-1763
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• 2002

Stress and displacement fields for a propagating crack in a functionally gradient material (FGM) which has shear modulus as $\mu$=$\mu$$\_$0/(1＋ζX) are derived. The equations of motion in FGM which is nonhomogeneous material are different from those of homogeneous material. The stress intensity factors in stress fields have influence on odd terms of γ$\^$n/2-1/(n=1,3,5,...,) but stress at crack tip only retains term of γ$\^$-1/2/, where the γ is a radius of cylindrical coordinates centered at crack tip. When the FGM constant ζ is zero or γ→0, the fields for FGM are almost same as the those for isotropic material.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.104-108
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• 1992

국소가열 가공방법은 종래 사용 되어온 온간,열간 가공의 경우와는 달리 프레스 성형의 응력조건 또는 양긱,열(온도)에 의한 재료 성질의변화 등을 고려하여, 가공하는 박판의 필요 부분을 선택적으로가열, 냉각 또는 두가지를 조합하여 처리하는 것이다. 온도 구배의 영향이 박판 성형의 공정에 많은 영향을 줌에도 불구하고 종래의 박판 성형가공은 주로 열을 고려하지않은 성형해석이 대부분이었고 열을 고려 하였다라도 대 부분이 실험에의존 한 방법이었다. 그러나 실제의 공정 설계에서 실험만을 통한 공정 변수의규명은 많은 노 력과 시간을 필요로 하기 때문에 컴퓨터를 통한 시뮬레이션의 필요성이 대두 되었다. 본 연구는 박판 축대칭 온도 구배와, 변형해석을 유한 요소적 방법을 통해 행하고 이를 실제 공정 설계에 적용할 수있도록 도움을 주고자 하는 데에 있다.

• Journal of Power System Engineering
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• v.1 no.1
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• pp.61-69
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• 1997

본 연구는 동심환형관에서 거칠기가 없이 매끈한 경우, 내측벽에 만, 외측벽에 만, 그리고 양측 모두에 거칠기가 있는 4경우에 대해 직경비가 0.26, 0.39, 그리고 0.56일 때 벽면에 설치된 거칠기 위치들이 난류유동장에 미치는 효과를 실험적으로 조사하고자 한다. 최대속도와 전단응력이 0인 지점들, 시간평균속도의 구배들, 그리고 와확산계수들을 X형 열선풍속계와 이중 피토튜브를 사용하여 측정하였다. 본 연구를 통하여 동심환형관에 설치된 거칠기들이 난류유동에 미치는 효과에 대한 정량적자료를 제시할 수 있었다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.231-238
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• 2015

Sapphire single crystals have been highlighted for epitaxial of gallium nitride films in high-power laser and light emitting diode industries. Among the many crystal growth methods, vertical Bridgman process is an excellent commercial method for growing high quality sapphire crystals with c-axis. In this study, the thermally induced stress in Sapphire during the vertical Bridgman crystal growth process was investigated using a finite element model. A vertical Bridgman process of 2-inch Sapphire was considered for the model. The effects of vertical and transverse temperature gradients on the thermal stress during the process were discussed based on the finite element analysis results.

• Tribology and Lubricants
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• v.31 no.6
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• pp.272-280
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• 2015

Recently, Luu suggested fatigue life equation that uses every term of the Crossland equation with stress gradient effect. Luu’s model, however, has a limit of being unable to coverage small radii that are less than a specified length. Furthermore, rolling model has a very small contact area compared to the rolling element size, and fatigue failure occurs on the small radius such as surface asperity by cyclic loading. Therefore, it is necessary to modify fatigue life equation in order to enable fatigue analysis for a small radius. In this paper, the fatigue life considering a stress gradient effect in rolling contact was obtained using Luu’s modified equation. Fatigue analysis was performed to study the effect of stress gradient on the fatigue life using newly adopted equation and to compare the results with pervious models. In order to do this, a series of simulation such as surface stress analysis, subsurface stress analysis, and fatigue analysis are conducted for two rolling balls of same size that contact each other. Through such a series of processes, the fatigue life can be calculated and equation that is proposed in this paper evaluates the fatigue life in case the contact area is small.

• Journal of Biomedical Engineering Research
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• v.21 no.4
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• pp.363-372
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• 2000

The present study investigated flow dynamics of a straight elastic blood vessel under sinusoidal flow conditions in order to understand influence of wall motion and impedance phase angle(time delay between pressure and flow waveforms) on wall shear stress distribution using computational fluid dynamics. For the straight elastic tube model considered in the our method of computation. The results showed that wall motion induced additional terms in the axial velocity profile and the pressure gradient. These additional terms due to wall motion reduced the amplitude of wall shear stress and also changed the mean wall shear stress. Te trend of the changes was very different depending on the impedance phase angle. As the wall shear stress increased. As the phase angle was reduced from 0$^{\circ}$to -90$^{\circ}$for ${\pm}$4% wall motion case, the mean wall shear stress decreased by 10.5% and the amplitude of wasll shear stress increased by 17.5%. Therefore, for hypertensive patients vulnerable state to atherosclerosis according to low and oscillatory shear stress theory.