• 한국생산제조학회지
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• 제6권3호
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• pp.58-64
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• 1997

A micromechanics model to describe the elastic behavior of fiber or whisker reinforced metal matrix composites was developed and the stress concentrations between reinforcements were investigated using the modified shear lag model with the comparison of finite element analysis (FEA). The rationale is based on the replacement of the matrix between fiber ends with the fictitious fiber to maintain the compatibility of displacement and traction. It was found that the new model gives a good agreement with FEA results in the small fiber aspect ratio regime as well as that in the large fiber aspect ratio regime. By the calculation of the present model, stress concentration factor in the matrix and the composite elastic modulus were predicted accurately. Some important factors affecting stress concentrations, such as fiber volume fraction, fiber aspect ratio, end gap size, and modulus ratio, were also discussed.

• 대한기계학회논문집B
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• 제25권1호
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• pp.18-28
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• 2001

The present study investigates flow dynamics between two dimensional compliant plates under sinusoidal flow conditions in order to understand influence of wall motion, impedance phase angle (time delay between pressure and flow waveforms), and non-Newtonian fluid on wall shear stress using computational fluid dynamics. The results showed that wall motion induced additional terms in the streamwise 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. The trend of the changes was very different depending on the impedance phase angle. As the impedance phase angle was changed to more negative values, the mean wall shear stress decreased while the amplitude of wall shear stress increased. As the phase angle was reduced from 0°to -90°under $\pm$4% wall motion, the mean wall shear stress decreased by 12% and the amplitude of wall shear stress increased by 9%. Therefore, for hypertensive patients who have large negative phase angles, the ratio of amplitude and mean of the wall shear stress is raised resulting in a more vulnerable state to atherosclerosis according to the low and oscillatory shear stress theory. We also found that non-Newtonian characteristics of the blood protect atherosclerosis by decreasing the oscillatory shear index.

• 한국방재학회 논문집
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• 제8권2호
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• pp.97-103
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• 2008

Determination of stress-strain relationship in torsional tests is complicated due to nonuniform stress-strain variation occurring linearly with the radius in a soil specimen in torsion. The equivalent radius approach is adequate when calculating strain at low to intermediate strains, however, the approach is less accurate when performing the test at higher strain levels. The modified equivalent radius approach was developed to account for the problem more precisely. This approach was extended to generate the plots of equivalent radius ratio versus strain using modified hyperbolic and Ramberg-Osgood models. Results showed the effects of soil nonlinearity on the equivalent radius ratio curves were observed. Curve fitting was also performed to find the stress-strain relationship by fitting the theoretical torque-rotation relationship to measured torque-rotation relationship.

• 한국농공학회지
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• 제30권4호
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• pp.134-153
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• 1988

This paper was carried out to investigate the existence of a unique stress- strain behavior by obtaining some factors influencing the time dependent stress- strain behavior of clay. The results obtained from this study were summarized as follows ; 1. The relationship between stress ratro and strain in normally consolidated clay was in- dependent on pre-shear consolidation pressure. Therefore, shear strain could be expressed as a function with stress ratio. 2. The constitutive equation of shear strain on Modified Carn Clay Model coincided better with the observed value than Cam Clay Model. 3. The relationships between deviator stress and shear strain, between pore water pressure and shear strain were unified by the mean equivalent pressure. 4. The shear strain contour in norrnally consolidated clay was increased linearly through origin, but that in overconsolidated clay was not in accordance with the result of the former. 5. Because the effective stress path of normally consolidated clay was unified by the mean equivalent pressure, state boundary surface in (e,p,q) space was transformed into two dimensional surface. But it was considered to be suitable that the unified stress- strain in overconsolidated clay be expressed by a function with overconsolidation ratio. 6. The deviator for constant strain was increased linearly with increment of strain rate ($\varepsilon$) on semi-log scale, but pore water pressure was decreased. 7. The behavior of stress relaxation was transformed from linear to curvilinear with inc - rement of strain rate before stress relaxation test, and pore water pressure was increased in total range. 8. The strain of creep was increased linearly with increment of time on semi-log scale. The greater the strain rate before creep test became, the greater the increment of strain of creep became. And the pore water pressure during creep test was increased generally with increment of time on semi-log scale.

• Geomechanics and Engineering
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• 제20권5호
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• pp.371-384
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• 2020

A settlement prediction method based on shear wave velocity measurements and soil nonlinearity was recently developed and verified by means of centrifuge tests. However, the method was only applicable to heavily overconsolidated soil deposits under enlarged yield surfaces. In this study, the settlement evaluation method was refined to consider the stress history of the sublayer, based on an overconsolidation ratio evaluation technique, and thereby incorporate irrecoverable plastic deformation in the settlement calculation. A relationship between the small-strain shear modulus and overconsolidation ratio, which can be determined from laboratory tests, was adopted to describe the stress history of the subsurface. Based on the overconsolidation ratio determined, the value of an empirical coefficient that reflects the effect of plastic deformation over the elastic region is determined by comparing the overconsolidation ratio with the stress increment transmitted by the surface design load. The refined method that incorporate this empirical coefficient was successfully validated by means of centrifuge tests, even under normally consolidated loading conditions.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.127-136
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• 2013

In this study, atomistic simulations are performed to study the effect of Al solute on the behaviour of edge dislocation in Mg alloys. After the dissociation of an Mg basal edge dislocation into two Shockley partials using molecular mechanics, the interaction between the dislocation and Al solute at different temperatures is studied using molecular dynamics. It appears from the simulations that the critical shear stress increases with the Al solute concentration. Comparing with the solute effect at T = 0 K, however, the critical shear stress at a finite temperature is lower since the kinetic energy of the atoms can help the dislocation conquer the energy barriers created by the Al atoms. The velocity of the edge dislocation decreases as the Al concentration increases when the external shear stress is relatively small regardless of temperature. The Al concentration effect on the dislocation velocity is not significant at very high shear stress level when the solute concentration is below 4.0 at%. Drag coefficient B increases with the Al concentration when the stress to temperature ratio is below 0.3 MPa/K, although the effect is more significant at low temperatures.

• 터널과지하공간
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• 제9권3호
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• pp.194-203
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• 1999

본 연구에서는 록볼트의 역학적 거동을 파악하기 위하여 지하공동에 설치된 단일 록볼트에 발생하는 축응력 분포, 록볼트-그라우트 접촉면에서의 전단응력 분포와 중립점의 위치를 분석하였으며, 현장의 다양한 지질조건에 대한 록볼트의 보강효과를 분석하기 위하여 여러가지 지반조건과터널크기에서 록볼트의 설치간격과설치길이를 변화시키며 전산해석을 수행하였다. 전산해석결과, 최대 인장응력 및 전단응력의 분포를 파악할 수 있었으며, 중립점의 위치에 영향을 주는 인자가 공동의 굴착폭임을 알 수 있었다. 또한 패턴볼팅으로 보강된 원형공동에서 록볼트에 의한 암반의 봉압효과는 응력 증가비를 사용하여 분석하였으며, 소성대 감소효과와지반 변위 감소효과는 각각 소성대 감소비와 변위 감소비를 사용하여 분석하여 록볼트의 보강효과 경향을 파악할 수 있었다. 이러한 보강효과의 경향분석 결과는 실제 터널의 안정적 설계에 적용할 수 있을 것으로 판단된다.

• 대한기계학회논문집A
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• 제23권6호
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• pp.1001-1010
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• 1999

Thermo-mechanical behavior of discontinuous shape memory alloy(SMA) reinforced polymeric composite has been studied using modified shear lag theory and finite element(FE) analysis with 2-D multi-fiber model. The aligned and staggered models of short-fiber arrangement are employed. The effects of fiber overlap and aspect ratio on the thermomechanical responses such as the thermal expansion coefficient are investigated. It is found that the increase of both tensile stress(resistance stress) in SMA fiber and compressive stress in polymer matrix with increasing aspect ratio is the main cause of low thermal deformation of the composite.

• 대한의용생체공학회:의공학회지
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• 제23권3호
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• pp.181-187
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• 2002

일정한 주기를 갖는 맥동유동에 대하여 혈관이 확장될 때 나타나는 동맥류 내부에서의 유동 및 벽면전단응력의 특성을 2차원적으로 고찰하였다. 상용 소프트웨어를 이용하여 직경비 1.5. 2.0 및 2.5 그리고 Womersley 수 15.47에 대한 복부대동맥내의 유동 현상을 수치해석하였다. 해석결과 동맥류 상단부에서 형성된 재순환유동은 시간의 흐름에 따라 생성과 소멸을 반복하였고. 시간이 3.19초인 경우, 동맥류 입구부 상단 근처에서 매우 미약한 재순환유동이 발달하고 있음을 예상할 수 있었다. 그리고 직경비가 증가할수록 동맥류 말단부에서 전단응력의 변화의 폭이 증가하였고 최대 전단응력의 값도 증가하는 것을 알 수 있었다. 그러나 최대 벽면전단응력의 발생 위치는 직경비의 변화와 거의 무관하였으며 동맥류 말단부 근처 (z : 35mm)에서 발생하였다

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.311-317
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• 2008

This study was carried out to improve our understanding about the influence of silt content on the stress-strain of sand under cyclic loading. Soil specimens were prepared by wet-tamping method as same void ratio and specimen's silt contents on total weights was changed from 0% to 20%. Also, effects of the silt contents on the stress-strain response were studied at different anisotropic consolidation ratio, Kc=1.0, 1.5, 2.0 condition. As a result, cyclic shear strength decreased as silt contents increased in same stress ratios. In same silt contents, cyclic shear strength increased as Kc increased in lower silt contents, but in higher silt contents, it had reverse results.