• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 전자세라믹스 센서 및 박막재료 반도체재료 일렉트렛트 및 응용기술
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• pp.43-46
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• 2000

In this paper, the stress and transient currents associated with the on and off time of applied voltage were used to measure the density and distribution of high voltage stress induced traps in thin silicon oxide films. The transient currents were due to the discharging of traps generated by high stress voltage in the silicon oxides. The trap distributions were relatively uniform near both cathode and anode interface. The trap densities were dependent on the stress polarity. The stress generated trap distributions were relatively uniform the order of $10^{11}\sim10^{21}$[states/eV/$cm^2$] after a stress. The trap densities at the oxide silicon interface after high stress voltages were in the $10^{10}\sim10^{13}$[states/eV/$cm^2$]. It appear that the stress and transient current that flowed when the stress voltage were applied to the oxide was caused by carriers tunneling through the silicon oxide by the high voltage stress generated traps.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.539-542
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• 2002

The role of disk clamp is to fasten disks to motor and to prevent the slip of disks during operation. This paper examined the effects of the design parameters of disk clamp - thickness, contact radius and cross-sectional shape -on the clamping force and circumferential stress distribution of disk. The large stress variation in circumferential direction results in large disk waveness and will increase repeatable run-out (RRO) finally. The disk clamp-disk-disk spacer system is modeled and the FE analysis is performed by ANSYS. The disk clamp with large contact radius shows more uniform stress distribution than the one with small contact radius and the stiffness variation around circumferential direct ion or the addition of the bending sect ion can make stress distribution uniform.

• Geomechanics and Engineering
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• 제17권2호
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• pp.145-156
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• 2019

Since behaviors of loose, dense, silty sands vary under seismic loading, understanding the liquefaction mechanism of sandy soils continues to be an important challenges of geotechnical earthquake engineering. In this study, 36 deformation controlled cyclic simple shear tests were performed and the liquefaction potential of the sands was investigated using three different relative densities (40, 55, 70%), four different effective stresses (25, 50, 100, 150 kPa) and three different shear strain amplitudes (2, 3.5, 5%) by using energy based approach. Experiments revealed the relationship between per unit volume dissipated energy with effective stress, relative density and shear strain. The dissipate energy per unit volume was much less affected by shear strain than effective stress and relative density. In other words, the dissipated energy is strongly dependent on relative density and effective stress. These results show that the dissipated energy per unit volume is very useful and may contain the non-uniform loading conditions of the earthquake spectrum. When multiple regression analysis is performed on experiment results, a relationship is proposed that gives liquefaction energy of sandy soils depending on relative density and effective stress parameters.

• Structural Engineering and Mechanics
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• 제53권4호
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• pp.703-723
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• 2015

In this paper optimization of volume fraction distribution in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and subjected to steady state thermal and mechanical loadings is considered. The finite element method with graded material properties within each element (graded finite elements) is used to model the structure. Volume fractions of constituent materials on a finite number of design points are taken as design variables and the volume fractions at any arbitrary point in the cylinder are obtained via cubic spline interpolation functions. The objective function selected as having the normalized effective stress equal to one at all points that leads to a uniform stress distribution in the structure. Genetic Algorithm jointed with interior penalty-function method for implementing constraints is effectively employed to find the global solution of the optimization problem. Obtained results indicates that by using the uniform distribution of normalized effective stress as objective function, considerably more efficient usage of materials can be achieved compared with the power law volume fraction distribution. Also considering uniform distribution of safety factor as design criteria instead of minimizing peak effective stress affects remarkably the optimum volume fractions.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.87-90
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• 2001

In particle or short-fiber reinforced composites, cracking of the reinforcements is a significant damage mode because the broken reinforcements lose load carrying capacity. This paper deals with elastic stress distributions and load carrying capacity of intact and cracked ellipsoidal inhomogeneities. Three dimensional finite element analysis has been carried out on intact and broken ellipsoidal inhomogeneities in an infinite body under pure shear. For the intact inhomogeneity, as well known as Eshelby(1957) solution, the stress distribution is uniform in the inhomogeneity and non-uniform in the surrounding matrix. On the other hand, for the broken inhomogeneity, the stress in the region near crack surface is considerably released and the stress distribution becomes more complex. The average stress in the inhomogeneity represents its load carrying capacity, and the difference of average stresses between the intact and broken inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The load carrying capacity of the broken inhomogeneity is expressed in terms of the average stress of the intact inhomogeneity and some coefficients. It is found that the broken inhomogeneity with higher aspect ratio still maintains higher load carrying capacity.

• 대한기계학회논문집
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• 제17권7호
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• pp.1794-1804
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• 1993

The thermal stress intensity factors for interface cracks of Griffith and symmetric lip cusp types under vertical uniform heat flow in a finite body are calculated by boundary element method. The boundary conditions on the crack surfaces are insulated or fixed to constant temperature. The relationship between the stress intensity factors and the displacements on the nodal point of a crack tip element is derived. The numerical values of the thermal stress intensity factors for interface Griffith crack in an infinite body and for symmetric lip cusp crack in a finite and homogeneous body are compared with the previous solutions. The thermal stress intensity factors for symmetric lip cusp interface crack in a finite body are calculated with respect to various effective crack lengths, configuration parameters, material property ratios and the thermal boundary conditions on the crack surfaces. Under the same outer boundary conditions, there are no appreciable differences in the distribution of thermal stress intensity factors with respect to each material properties. But the effect of crack surface thermal boundary conditions on the thermal stress intensity factors is considerable.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.561-564
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• 1999

The uniform state of prestress in a fully prestressed concrete members shows reductions of more than half of the initial prestress in the construction and coupling joint vicinity. Especially, at a zone x/d=0.2 above the construction joint where at the edge of the member, a quite localized reduced stress state of 1/3 of uniform stress is encountered. Five full-scale test specimens were segmentally constructed and post-tensioned and analytic models is used to verify and validate measured test results. The encountered highly nonuniform stress/strain state in the coupling joint vicinity requires special design consideration for the successful application of tendon couplers.

• 대한기계학회논문집A
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• 제23권6호
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• pp.961-967
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• 1999

A model is constructed to evaluate the mode III stress intensity factor(SIF) for orthotropic three-layered material with a center crack subjected to uniform anti-plane shear loading. A mixed boundary value problem is formulated by Fourier integral transform method and a Fredholm integral equation of the second kind is derived. The integral equation is numerically analyzed to evaluate the effects of the ratio of shear modulus, strength of each layer and crack length to layer thickness on the stress intensity factor.

• 대한기계학회논문집
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• 제13권4호
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• pp.625-635
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• 1989

본 논문에서는 이 방법을 사용하여 glass/epoxy와 graphite/epoxy 유한평판이 균일응력과 균일변위 경계조건을 받을 때 평판 종횡비 H/W를 1,2,3, 균열길이와 폭의 비 L/W를 0.1부터 0.7까지, 균열각도를 0, 30, 45, 60으로 변화 시키면서 응력강도수정계수를 구하려고 한다.

• Structural Engineering and Mechanics
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• 제70권3호
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• pp.279-287
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• 2019

This paper intends to introduce a near-tip grid refinement and to explore its usefulness in the crack analysis by the natural element method (NEM). As a sort of local h-refinement in FEM, a NEM grid is locally refined around the crack tip showing the high stress singularity. This local grid refinement is completed in two steps in which grid points are added and Delaunay triangles sharing the crack tip node are divided. A plane-state plate with symmetric edge cracks is simulated to validate the proposed local grid refinement and to examine its usefulness in the crack analysis. The crack analysis is also simulated using a uniform NEM grid for the sake of comparison. The near-tip stress distributions and SIFs that are obtained using a near-tip refined NEM grid are compared with the exact values and those obtained using uniform NEM grid. The convergence rates of global relative error to the total number of grid points between the refined and non-refined NEM grids are also compared.