• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2001년도 춘계학술대회 논문집
• /
• pp.249-256
• /
• 2001

This study investigated the shear stiffness of level of small strain with time effect. Time effect consists of rest time, loading rate of recent and current stress path. In addition, for the measurement of small strain, overconsolidated state was represented in a triaxial cell, and drained stress path tests were carried out. Test results show that the loading rate of recent stress path has no effects on the stiffness of very small strain, but the shear stiffness of level of small strain increases with it. Finally, the rest time and the loading rate of current stress path have the effects on the shear stiffness of initial and small strain.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1999년도 가을 학술발표회 논문집
• /
• pp.351-356
• /
• 1999

An elasto-plastic constitutive model was Proposed, in which the behavior at small-to-large strain level can be modeled. From a mathematical approach it was proved that the model includes the previous successful models. The experimental results of a series of resonant column tests, torsional shear tests and triaxial tests were verified and as a result the proposed model could predict small-to-large strain behavior more consistently and accurately than the hyperbolic model and the Ramberg-Osgood model for a weathered granitic soil.

• Geomechanics and Engineering
• /
• 제15권3호
• /
• pp.919-925
• /
• 2018

Stress-strain responses of weak-to-strong carbonate rocks used for tunnel construction were studied. The analysis of applicability of exponential stress-strain models based on Haldane's distribution function is presented. It is revealed that these exponential equations presented in transformed forms allow us to predict stress-strain relationships over the whole pre-failure strain range without mechanical testing of rock samples under compression using a press machine and to avoid measurements of axial failure strains for which relatively large values of compressive stress are required. In this study, only one point measurement (small strain at small stress) using indentation test and uniaxial compressive strength determined by a standard Schmidt hammer are considered as input parameters to predict stress-strain response from zero strain/zero stress up to failure. Observations show good predictive capabilities of transformed stress-stress models for weak-to-strong (${\sigma}_c$ <100 MPa) heterogeneous carbonate rocks exhibiting small (< 0.5 %), intermediate (< 1 %) and large (> 1 %) axial strains.

• 항공우주시스템공학회지
• /
• 제14권6호
• /
• pp.91-99
• /
• 2020

This study proposes a finite element (FE) model for predicting the bending strength of small gears used in electro-mechanical actuators for aircraft. First, a strain gauge was attached to the tooth root of test gear, and the strain was measured. Subsequently, the FE model was applied to calculate the strain of the test gear, and the modeled strain was compared with the experimental strain. The results confirmed that the FE strain was very close to the experimental strain and the FE model was valid. This FE model was extended to the bending strength analysis of several small gear tooth models. The bending strengths of all the tooth models were almost identical to the ISO theoretical bending strength. Finally, the FE model was validated and the reliability of the modeled bending strength was evaluated through the strain measurement experiment.

• Geomechanics and Engineering
• /
• 제5권1호
• /
• pp.57-70
• /
• 2013

Constant rate of strain (CRS) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in Saga Plain of Kyushu Island, Japan. The coefficients of consolidation ($c_{\nu}$) were interpreted from the CRS test results by small- and large-strain theory. Large-strain theory was found to interpret smaller $c_{\nu}$ values and less strain rate effect on $c_{\nu}$ than that by small-strain theory. Comparing the theoretical strain distributions within a soil specimen to those obtained by numerical simulation shows that the small-strain theory can be used only for the dimensionless parameter $c_{\nu}/\dot{\varepsilon}H_0^2{\geq}50$ (where $\dot{\varepsilon}$ is strain rate and $H_0$ is the specimen height), and the large-strain theory can be used for a larger range of strain rates. Applying the criterion to undisturbed Ariake clay with a $c_{\nu}$ value of about $1{\times}10^{-7}\;m^2/s$, it is suggested that the large-strain theory should be adopted for calculating the $c_{\nu}$ value when $\dot{\varepsilon}$ > 0.03%/min.

• 한국지반공학회논문집
• /
• 제18권1호
• /
• pp.41-48
• /
• 2002

공중낙하법에 의해 만든 등방압밀 모래공시 체를 미소변형률 측정장치를 사용한 평면변형률압축시험을 실시하여 미소변형률에서 파괴후까지의 응력-다이레이턴시(stress-dilatancy) 관계를 연구하였다. 세계 각국의 주요 연구기관에서 사용되고 있는 7종류의 연구용 표준사 공시체를 멤브레인의 관입에 의한 오차와 변위를 외부에서 측정함으로 하여 생기는 오차(bedding error) 등의 영향을 제거하여 측정한 최대주응력방향의 변형률과 최소주응력방향의 변형률을 각각 0.0001%에서 파괴 시까지의 응력-변형률 관계를 얻었다. 그 결과 미소변형률 수준에서 파괴 시가지의 주응력비-주변헝률증분비 관계는 과압밀비 및 구속압에 거의 영향을 받지 않고 동일하였다. 또한 미소변형률에서는 이방성이 주응력비-주변형률증분비 관계에 미치는 영향은 거의 없지만, 파괴 부근에서의 K값의 크기는 $\delta$에 따라 다른 값을 나타내었다. 한편, K값은 모래의 종류에 따라 다른 값을 나타내었다. 전체적으로 Rowe의 응력-다이레이턴시식은 미소변형를에서 파괴까지 근사적으로 성립한다는 것을 알았다.

• 한국지반공학회지:지반
• /
• 제13권4호
• /
• pp.109-120
• /
• 1997

공용하중 상태에서 지반이 경험하는 변형률 크기는 0.1~1% 미만임이 밝혀지고 있다. 변형특성을 보다 엄밀히 평가하기 위하여는 미소변형률 영역에서의 신뢰성 있는 변형측정이 가능한 현장시험기기의 개발이 필요하다. 본 연구의 목적은 공내째하시험기(PMT)를 사용하여 지반의 미소변형률 전단탄성계수를 측정하는 것이다. 공내재하시험에서 시추공 설치에 따른 주위 지반의 교란효과를 제거하기 위하여 초기 하중재하단계가 아닌 역재하-재재하 단계에서 PMT 주위지 반의 응력상태 및 변형률 크기를 고려하여 미소변형률 잔단탄성계수를 결정하였다. 실내 토조에서 성형한 모래시료와 화강풍화토 현장지반에서 시험을 수행하였으며,시험결과로부터 본 연구 에서 사용한 PMT시험은 변형률 크기 10-2%~0.5% 범위에서 신뢰성 있는 전단탄성계수 측정이 가능하였다. 또한 변형률 크기를 고려하여 다른 실내외시험에서 결정된 전단탄성계수와 비교 하면 서로 잘일치하는 결과를 얻을 수 있었다.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2001년도 봄 학술발표회 논문집
• /
• pp.139-146
• /
• 2001

Undrained triaxial tests were peformed for a weathered soil, which includes local measurement using LVDT The behavior from small In large strain conditions could be evaluated consistently through a triaxial test, The stress-strain relationship of undisturbed samples were compared with the disturbed and the shear moduli in the small strain level had the almost same values. Especially the shear moduli were mostly affected by the initial condition of water contents. An anisotropic hardening model based on the total stress concept could predict the stress-strain relationship accurately, which makes it possible to analyze the geotechnical problem reasonably for the weathered soil.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 춘계 학술발표회
• /
• pp.448-456
• /
• 2010

The mechanical behavior of granular soils is affected by particle bonding including natural cementation. This study addresses a simple model of small strain stiffness and salt concentration based on wave measurements of salt-cemented particulate media. Published models of artificially cemented soils with different curing methods and several types of cementation agents are reviewed. Glass beads with the median diameter of D50 = 0.5mm are prepared in rectangular cells using the water-pluviated method in salt water with different concentrations. Piezo disk elements and bender elements embedded in the cell are used for the measurements of compressional and shear waves. The relationships between elastic wave velocities and salt concentration show an exponential function. The measured small strain stiffness matches well the predicted small strain stiffness based on micromechanics for simple cubic monosized sphere particles. This study demonstrates that the salt concentration in salt-cemented specimen may be evaluated by using elastic wave velocities.

• 한국지반공학회논문집
• /
• 제16권1호
• /
• pp.65-73
• /
• 2000

본 연구에서는 미소변형률에서 대변형률까지의 거동을 모델할 수 있는 탄소성 구성모델을 개발하였다. 제안된 구성모델은 일반 등방경화규칙에 근거한 비등방 경화규칙과 전응력 개념을 토대로 개발하였다. 그리고 제안된 구성관계가 기존의 대표적 구성모델을 포함하고 있음을 수학적으로 입증하였다. 국내 화강풍화토에 대한 공진주시험, 비틂전단시험, 삼축시험 등 일련의 실내시험 결과를 이용하여 검증한 결과, 쌍곡선 모델 및 Ramberg-Osgood모델과 비교하여 제안된 모델은 미소변형률에서 대변형률까지의 거동을 더욱 일관되고 정확하게 모델할 수 있다. 또한 비틂전단시험 결과와의 비교에서는, 미소변형률 조건에서 나타나는 비선형성을 적합하게 예측할 수 있었다.