• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1486-1494
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• 1991

본 연구에서는 분말단조 공정의 유한요소 컴퓨터 시뮬레이션을 위한 기초연구 로 다공질예비성형체의 기지(matrix)인 합금강의 변형률 속도와 온도에 따른 일축 압 축하의 열-점소성 거동을 조사하였다. 변형률 속도와 온도의 영향을 동시에 고려하 기 위하여 변형률 속도 .epsilon.=$10^{-4}$, $10^{-2}$ 및 $10^{-1S-1}$과 온도범위 800~ 1200.deg. C에 대하여 실험하였다.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.335-342
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• 2003

In order to analyze the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at whole strain ranges, needs to be developed. The pressuremeter is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. This paper introduces a new alternative, the cavity strain measuring system in pressuremeter designed for whole strain ranges of $10^{-5}$%∼20%. Not only in the synthetic calibration chamber but also in the field, the pressuremeter tests were performed to determine the compliance of the new developed pressuremeter system. The variation in shear modulus with strain amplitude above $5\times 10^{-2}$% was reliably determined by the developed pressuremeter. It is concluded that the major cause of error in small cavity strain measuring is not from the cavity strain measuring system but from the friction between measuring arm and membrane during unloading-reloading loops.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1027-1035
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• 2016

In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.

• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.137-145
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• 2003

In this study, direct tensile fatigue tests of the PS bar were performed in terms of diameter, minimum stress level, and maximum stress level. In the static test, the stress - strain curve and ultimate streng th of the PS bar were determined. Results of the fatigue test indicate that the diameter of the PS bar was not influenced by fatigue life. Minimum stress also had quite an influence on the fatigue of the PS bar. Thus, the fatigue characteristic equation was proposed in terms of stress range and minimum stress through statistical process. Strains on specimen that loaded direct tension were measured in the fatigue test, with the secant modulus of elasticity calculated from measured strains. The strain development consisted of three different stages, i.e., rapid increases during the initial fatigue life, uniform increases during the middle stage, and rapid increases until failure. The secant modulus of elasticity decreased during the fatigue life with increasing strain. However, stress level seemed to have no influence on the secant modulus of elasticity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.321-329
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• 2009

Laboratory compressive test was conducted on 6 different types of rock in order to investigate the characteristic of critical strain under uniaxial and triaxial stress condition. The results of uniaxial compressive test mostly ranged within 1~100MPa, the critical strain was also located between 0.1~1.0%. Therefore the results distributed within the upper and lower boundary proposed by Sakurai (1982). And the failure/critical strain ratio (${\varepsilon}_f/{\varepsilon}_0$) showed between 1.0~1.8 value depending on the uniaxial compressive strength. The results of critical strain by triaxial compressive test showed below 0.8% value for all test, the M value calculated from uniaxial and triaxial compressive test results ranged 1.0~8.0 for most of rock specimens. It is concluded that failure strain (${\varepsilon}_{f3}$) of rock mass, which is in triaxial stress condition is larger than the results of uniaxial stress condition (${\varepsilon}_{f1}$) by 1.0~8.0 times and value showed 1.0~1.8 larger value than critical strain (${\varepsilon}_{01}$). Therefore it is a conservative way for rock tunnel to use critical strain (${\varepsilon}_{01}$) calculated from a uniaxial compressive strength on tunnel displacement monitoring.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.765-772
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• 2011

The present study summarizes a series of compressive tests on concrete cylinder in order to examine the stressstrain relationship of alkali-activated (AA) slag concrete. The compressive strength and unit weight of concrete tested ranged from 8.6 MPa to 42.2 MPa and from $2,186kg/m^3$ to $2,343kg/m^3$, respectively. A mathematical equation representing the complete stress-strain curve was developed based on test results recorded from 34 concrete specimens. The modulus of elasticity, strain at peak stress, slopes of ascending and descending branches of stress-strain curves were generalized as a function of compressive strength and unit weight of concrete. The mean and standard deviation of the coefficient of variance between measured and predicted curves were 6.9% and 2.6%, respectively. This indicates that the stress-strain relationship of AA slag concrete is represented properly with more accuracy in the proposed model than in some other available models for ordinary portland cement (OPC) concrete.

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.93-105
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• 2000

일정변형률압밀사시험의 효율성 및 적용성을 구체화하기 위해 인공시료 또는 한정된 지역에서 채취한 불교란 점성토 시료가 아닌 광범위한 지역에서 채취한 불교란 점성토 시료에 대해 시험을 실시하였다. 시료채취의 대상지역은 우리나라의 서해안에서 동해안에 이르는 13개 지역이며, 29개의 불교란 자연시료를 채취하여 일정변형률압밀시험을 113회 실시하였다. 또한, 비교하기 위해 표준압밀시험도 병행하였다. 시험결과로부터 얻어진 압밀정수에 대한 공학적 특성을 고찰하였고, 회기분석을 통해 통계식을 제안하였다. 두 시험법에 의해 산출된 압밀정수를 비교 분석한 결과 수압비가 20% 이내인 범위에서는 일정변형률압밀시험의 변형률 속도가 압밀시험의 정수에 미치는 영향은 거의 없는 것으로 나타났다. 압축지수 및 압밀계수는 일정면형률시험의 결과 값이 표준압밀시험의 결과 값보다 크게 산출되었으나 일관성을 보였다. 또한, 선행압밀압력에 있어서는 두 시험법에 Cassagrande의 방법을 적용할 경우 서로 일치하는 것으로 나타났다. 본 연구로부터 일정변형률압밀시험을 사용하여 표준압밀시험에 상용하는 상호관계식 개발의 타당성을 확인할 수 있었다.

• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.129-136
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• 2001

본 논문에서는 석탄회 매립지반의 액상화 가능성을 평가하기 위해 순수 모래시료와 더불어서 모래시료와 석탄회가 혼합된 모래시료에 대한 일련의 진동삼축실험을 변형률제어 방법으로 수행하였다. 실험결과 진동하중에 의해서 시료 내에 발생하는 간극수압의 크기는 작용하는 전단변형률의 크기에 심각하게 영향을 받고, 작용하는 전단변형률이 지반의 한계전단변형률 보다 작은 경우에는 진동수가 높은 조건에서도 간극수압이 발생하지 않음을 알았다. 또한 전단변형률이 약 0.1%보다 작고 한계전단변형률에 가까운 경우에는 순수 모래시료와 비교하여 본 논문에서 조사한 석탄회 함유율 범위 (10%~30%)의 시료에서 간극수압이 더 크게 발생하였다. 반면에, 전단변형률이 큰 경우에는 순수 모래시료에서 간극수압이 크게 발생하는 추세를 보였다. 반복 전단에 따른 간극수압의 발생량은 전반적으로 석탄회 함유율이 증가할수록 커지는 경향을 보였다. 이러한 결과를 근거로 해안이나 하천에 인접한 한계지 개발에 있어서 사질토에 석탄회를 혼합 매립하여 지반을 조성하는 경우에 액상화에 대해서 불안정한 지반이 될 가능성이 있는 것으로 판단되었다.

• Journal of the Korean Geotechnical Society
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• v.28 no.12
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• pp.17-25
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• 2012

FEM requires the stress-strain relationship equations for numerical analyses. However, most formulations for the stress-strain relationship published up to the present are not satisfactory enough to properly express all the levels from the small strain to the peak. Tatsuoka and Shibuya (1991) suggested a new single formulation applicable not only to a wide range of geo-materials from soft clay to soft rock, but also to a wide range of strain levels from $10^{-6}$ to $10^{-2}$. The plain strain compression test is carried out to seven samples of research standard sand specimens and two samples of glass beads, which have been used at world-renowned research institutes. In this study, strains of the maximum principal stress (${\sigma}_1$) and the minimum principal stress (${\sigma}_3$) were thoroughly measured from $10^{-6}$ to $10^{-2}$, and the result, applied to Tatsuoka and Shibuya's new formulation, coincided closely with the measured data of the stress-strain relationship from the small strain to the peak.

• Geotechnical Engineering
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• v.14 no.4
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• pp.33-46
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• 1998

Anisotropy of stiffness, from extremely small strains to post-failure strains, of isotropically consolidated air-pluviated sands in plane strain compression was studied by using the newly developed instrumentation for small strain measurements. Seven types of sand of the world-wide origins were tested, which have been extensively used for research purposes. Stress-strain at the specimen boundaries. It was found that the maximum Young's modulus $E_{max}$ was irrespective of the angle $\delta$ of the $\delta_1$ direction relative to the bedding plane. However, the normalized$ E_{max}$ was varied with the types of sand. Furthermore, the dependency of the strain and stress level on the stiffness was increased as $\delta$ decreased.