• 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.

• Magazine of the Korea Concrete Institute
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• v.9 no.5
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• pp.197-206
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• 1997

본 연구에서는 기존의 초고강도 콘크리트에 대한 실험자료를 근거로 합리적인 통계적 기법을 이용하여 초고강도 콘크리트의 설계 실용화를 위한 응력-변형율 관계 모델과 응력분포 모델을 제안하는 것이 목적이다. 이를 위하여 첫째, 콘크리트의 응력-변형율 특성을 결정하는 재료 변수들(탄성계수, 최대 압축강도시 변형율 등)에 대한 검토를 수행하였다. 둘째, 이를 바탕으로 일반성과 정확성을 동시에 갖춘 초고강도 콘크리트(700~1400kg/$\textrm{cm}^2$)에 적합한 응력-변형율 모델을 제안, 비교, 고찰하엿다. 셋째, 제안된 응력-형율 모델로부터 초고강도 콘크리트 구조의 극한강도를 평가하기에 적합한 응력분포모델을 제안, 일반성과 정확성을 비교 검증하였다.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.108-116
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• 1991

In the non-linear behavior of many materials, there is difference between the monotonic behavior by static load and the cyclic behavior by cyclic load. In particular, the short fatigue cracks to propagate in elasto-plastic stress concentrations(notches), are governed significantly by the cyclic behavior of materials. Accordingly, it is needed to investigate and compare the monotonic and cyclic behavior of materials. In the pressent study, the stress-strain relations of materials by monotonic and cyclic load tests were examined for 2 kinds of steels(SS41, HT80) and 5 kinds of Al-alloys(A5083-O, A6N01-T5, A7N01-T4, A7016-T6, A7178-T6). And the constants for mechanical properties of the materials were determined by experimental results, Moreover, when a notch was subjected to cyclic load, the effect of cyclic hardening property of materials on the variation of stress-strain amplitude in the notch tip was discussed by the application of Neuber's rule and experiments for a center notched plate.

• Korean Journal of Materials Research
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• v.5 no.3
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• pp.371-378
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• 1995

YBCO 산화물 초전도체의 초소성 변형에 대한 최적 변형조건을 파악하고자 80$0^{\circ}C$~93$0^{\circ}C$의 온도범위에서 1.0 $\times$ $10^{-3}$s^{-1}$!1.0 $\times$ $10^{-7}$s^{-1}$의 초기변형속도로 압축시험을 수행하였다. 변형속도 민감지수는 m=0.50 $\pm$ 0.1로 나타났다. 이는 결정립계 미끄러지\ulcornerㄹ 주 변형기구로 하는 초소성임을 의미한다. 결정립크기에 따른 유동응력과의 관계는 $\sigma$\propto$d^{1.8 $\pm$ 0.3}$의 지수함수식을 이루고 있으며 Nabarro-Hering 크\ulcorner과 상응하는 격자확산이 확산경로임을 보였다. 초소성 변형에 대한 활성화에너지는 Q=571 $\pm$ 30 kJ/mole이었다. 본 실험온도 구간에서 압축 변형시 변형속도, 변형응력 및 결정립크기에 따른 고온 변형거동 관계식은 $\varepsilon$=A$\sigma$^{2.00 $\pm$ 0.04 - 1.8 $\pm$ 0.3}$ exp(-571 $\pm$ 30kJ/RT)와 같이 유도 되었다. 본 실험조건에서 최적 초소성 변형조건은 86$0^{\circ}C$ 부금, 초기변형속도 ~1.0 $\times$ $10^{-4}$S^{-1}$이었다.

• Journal of the Korean Society for Precision Engineering
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• v.1 no.1
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• pp.23-29
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• 1984

소성역학에 의해서 소성가공중의 현상을 해석하여 제품의 형상, 강도, 잔유응력, 가공력, 가공한계 및 결함의 발생등을 견적하고 이것에 의해 가공기계의 강도, 강성 및 제어량등이 결정된다. 또 재질에 대한 지침이 얻어진다. 탄성론이나 소성론에서 경계치 문제는 응력젼위방정식, 응력의 경계조건, 변위에 관한 변위 스트레인 관계식과 변위의 경계조건, 그리고 응력과 스트레인을 관계시 키는 구성방정식으로 되어 있는 기초방정식으로 구성된다. 문제의 구성방정식은 재료의 거동이 매우 복잡하기 때문에 실제의 거동을 충실히 표시 할 수 없다. 재료의 이방성, 유한도형, 이방성주축의 회 전, 가공경화, 고온, 고속가공 등에 의해서 재료의 변형거동은 매우 복잡해진다. 이상의 정량적 고찰 과 전위 또는 결정의 슬립모델과 같은 정성적 고찰도 있다.

• Journal of the KSME
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• v.31 no.3
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• pp.293-299
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• 1991

단섬유보강 금속복합재료의 2차가공은 금속복합재료의 넓은 범위 응용을 위해 필히 요구된다. 여러 가공방법 중 하나인 열간압출시 보강섬유파괴 및 계면에서의 접합분리 및 균열발생이 없는 제조공정의 최적화를 위해서 가공시 내부조직의 소성변형 기구 규명보다 압출력에 의한 응력분 포와 기지재료와 보강섬유 사이 계면 변화 및 기계적 특성 관계규명이 정량적으로 요구된다. 본 글에서는 유한요소법을 이용하여 계면에서의 접합상태를 임의로 가정하여 압출조건에 따른 압 출후의 보강섬유 방향 및 계면균열 및 접합분리를 거시적으로 예측하고, advanced shear-lag을 이용하여 균열 전, 후의 응력. 변형관계를 미시적으로 규명할 수 있음을 제시하였다. 그러나 향후 현상적 모델인 shear-lag 모델을 수학적 모델인 균질화법에 도입하면 미시적. 거시적 거 동해석이 함께 요구되는 금속복합재료의 열간압출거동 해석을 일체적으로 행할 수 있어 효율적 이고 정확한 예측이 가능하리라고 사료된다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.454-464
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• 1987

The objective of this research is to analyze and evaluate the dynamic flow curve of metals under impact loading at both high strain rate (.epsilon.=1/h dh/dt > 10$\^$3/m/s/m) and large strain (.epsilon.=In h/h$\_$0/ > 1.0). A test method for dynamic compression of metal disc is described. The velocity of the striker face and the force on the anvil are measured during the impact period. From these primitive data the axial stress, strain, and strain rate of the disc are obtained. The Strain rate is determined by the striker velocity divided by the specimen height. This gives a slightly increasing strain rate over most of the deformation period. Strain rates of 100 to 10,000 per second are achieved. Attainable final strains are 150%. A discussion of several problem areas is presented. The friction on the specimen surfaces, the determination of the frictional coefficient, the influence of the specimen geometry (h$\_$0//d$\_$0/ ratio) on the friction effect, the lock-up condition for a given configuration, the friction correction factor, and the evaluation of several lubricants are given. The flow function(stress verus strain) is dependent on the material condition(e.g., prior cold work), specimen geometry, strain rate, and temperature.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.445-454
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• 2001

This paper is to study elasto-plastic behavior of shear deformed braced frames. Two types of frames are considered , X-type and K-type. The slenderness ratio has been used in the parametric study. The stress-strain curve is assumed tri-linear model, and considered the strain hardening range. The finite difference method is used to solve the load-displacement relationship of the braced frames. For the elastic slope and maximum load, experimental results are compared with theoretical results and its difference remains less than 10%. Therefore suggested method in this paper is reasonable.

• Geotechnical Engineering
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• v.13 no.2
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• pp.29-38
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• 1997

Strain softening is observed for geomaterials such as rocks when they are sheared. The proper computational modelling for strain softening is very important because this behavior is closely related to failure in geotechnical problems. In this paper, we have investigated the proper FEM techniques for modelling strain softening in order to simulate failure behavior numerically. In showing numerical examples, the effects of element shape, mesh pattern and of imperfection and the difference between small and large deformation theories, of displacement control and pressure control after peak have been discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.78-89
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• 1993

A new theory based on the modified momentum and energy conservation has been proposed in order to overcome the drawbacks included in previous theories which are used for the determination of dynamic yield stresses and the investigation of dynamic behavior of metals. Then the improvements suggested by the new theory have been manifested through the analysis of the error included in the measurement of deformed length and through the comparison between the new theory, existing theories, and experimental results performed by previous workers. Meanwhile rod impact test has been performed which uses a compressed- air system for the acceleration of flat-ended cylindrical free-cutting brass rods. From the geomtrical measurements of deformed length, the dynamic yield stress of free-cutting brass has determined.