• 소성∙가공
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• 제16권2호
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• pp.101-106
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• 2007

Uniaxial displacement controlled tests were performed on annealed Type 304 stainless steel at room temperature. A servo-controlled testing machine and strain measurement on the gage length were employed to measure the response to a given input. The test results exhibit that the flow stress increases nonlinearly with the strain rate and the relaxed stress at the end of the relaxation periods depends strongly on the strain rate preceding the relaxation test. The rate-dependent inelastic deformation behavior is simulated using a new unified viscoplasticity model that has the rate-dependent format of nonlinear kinematic hardening rule, which plays a key role in modeling the rate dependence of relaxation behavior. The model does not employ yield or loading/unloading criteria and consists of a flow law and the evolution laws of two tensor and one scalar-valued state variables.

• Computers and Concrete
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• 제1권4호
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• pp.417-432
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• 2004

An analytical model which can simulate the post-cracking nonlinear behavior of reinforced concrete (RC) members such as bars and panels subject to uniaxial and biaxial stresses is presented. The proposed model includes the description of biaxial failure criteria and the average stress-strain relation of reinforcing steel. Based on strain distribution functions of steel and concrete after cracking, a criterion to consider the tension-stiffening effect is proposed using the concept of average stresses and strains. The validity of the introduced model is established by comparing the analytical predictions for reinforced concrete uniaxial tension members with results from experimental studies. In advance, correlation studies between analytical results and experimental data are also extended to RC panels subject to biaxial tensile stresses to verify the efficiency of the proposed model and to identify the significance of various effects on the response of biaxially loaded reinforced concrete panels.

• 소성∙가공
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• 제24권3호
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• pp.194-198
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• 2015

Microstructure based FE simulations were conducted to investigate the micro-mechanical properties of ferrite-martensite dual-phase steels. The FE model was built based on real microstructure images which were characterized by optical microscopy through the thickness direction. Serial sectioned 2D images were converted into semi-2D representative volume elements (RVEs) model. Each RVE model was subjected to a non-proportional loading condition and the mechanical response was analyzed on both the macroscopic and microscopic levels. Macroscopically, stress-strain curves were described under tension-compression and tension-orthogonal tension conditions and the Bauschinger effect was well captured for both loading paths. In addition, micromechanical properties were investigated in the view of stress-strain partitioning and strain localization during monotonic tension.

• Computers and Concrete
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• 제18권2호
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• pp.201-214
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• 2016

In this paper, a multilaminate based model have been developed and presented to predict the strain hardening behavior of rock. In this multilaminate model, the stress-strain behavior of a material is obtained by integrating the mechanical response of an infinite number of predefined oriented planes passing through a material point. Essential features such as the variable deformations hypothesis and multilaminate model are discussed. The methodology to be discussed here is modeling of strains on the 13 laminates passing through a point in each loading step. Upon the presented methodology, more attention has been given to hardening in non-linear behaviour of rock in going from the peak to residual strengths. The predictions of the derived stress-strain model are compared to experimental results for marble, sandstone and dense Cambria sand. The comparisons demonstrate the ability of this model to reproduce accurately the mechanical behavior of rocks.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.477-484
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• 2000

Earthquake response analyses are conducted for the investigation of the ground shaking during the 1995 Hyogoken-nambu earthquake. Port Island a man made island with about 8{{{{ KAPPA m^2 }} area is chosen for this purpose Because earthquake measurement with vertical array was conducted there. Strain dependent characteristics of soil can be modeled well into Hardin-Drnevich Model. Four analyses are conducted : total stress analysis by equivalent linear method non-linear method. and two effective stress analyses. All analyses except equivalent linear analysis show fairy good agreement with observed record mainly because the non-linear behavior of Holocene clay layer has predominant effect on the behavior of fill, However detailed investigation show that effective stress analyses give much better prediction than total stress analyses.

• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 2002년도 제9회 학술 발표회 프로그램과 논문초록
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• pp.55-55
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• 2002

An alternative sigma factor as encoded by the $\sigma$$\^$B/ gene in Streptomyces coelicolor A3(2) was known to be involved in the differentiation and osmotic stress response. Protein expression profiles of wild-type and a $\sigma$$\^$B/ mutant strain of S coelicolor A3(2), which is impaired in defense against osmotic stress, were compared in the absence and presence of osmotic stress, using 2-dimentional gel electrophoresis.(omitted)

• Toxicological Research
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• 제35권1호
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• pp.25-35
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• 2019

The extracts of Plathymenia reticulata and Connarus favosus are widely used in the folk medicine. The potential protective effects of these extracts have been evaluated against cadmium in the yeast Saccharomyces cerevisiae, and against mercurial contamination in zebrafish Danio rerio. In yeast, both extracts efficiently protected the ${\Delta}ycf1$ mutant strain exposed to cadmium chloride restoring the growth, the expression of stress-response genes and decreasing the level of oxidative stress. In zebrafish, the supplementation of methylmercury-contaminated diet with both plant extracts similarly protected fish through the suppression of the methylmercury-induced lipid peroxidation, decrease of acetylcholinesterase activity, and restoring the expression levels of stress-response genes. This study particularly demonstrates the protective potential of both aqueous extracts against methylmercury, and could represent an interesting alternative for the Amazonian fish-eating communities to cope with the impact of chronic exposure to contaminated diets.

• KCI Concrete Journal
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• 제12권2호
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• pp.85-93
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• 2000

Potentially significant mechanical improvements in tension can be achieved by the incorporation of randomly distributed, short discrete fibers in concrete. The improvements due to the incorporation fibers significantly influence the composite stress - strain ($\sigma$-$\varepsilon$) characteristics. In general incorporating fibers in a plain concrete has relatively small effect on its precracking behavior. It, however, alters its post-cracking behavior quite significantly, resulting in greatly improved ductility, crack controls, and energy absorption capacity (or toughness). Therefore, a thorough understanding the complete tensile stress - strain ($\sigma$-$\varepsilon$) response of fiber reinforced concrete is necessary for proper analysis while using structural components made with fiber reinforced concrete. Direct tensile stress applied to a specimen is in principle the simplest configuration for determining the tensile response of concrete. However, problems associated with testing brittle materials in tension include (i) the problem related to gripping of the specimen and (ii) the problem of ensuring centric loading. Routinely, indirect tension tests for plain concrete, flexural and split-cylinder tests, have been used as simpler alternatives to direct uniaxial tension test. They are assumed to suitable for fiber reinforced concrete since typically such composites comprise 98% by volume of plain concrete. Clearly since the post-cracking characteristics are significantly influenced by the reinforcing parameters and interface characteristics, it would be fundamentally incorrect to use indirect tensile tests for determining the tensile properties of fiber reinforced concrete. The present investigation represents a systematic look at the failure and toughening mechanisms and macroscopic stress - strain ($\sigma$-$\varepsilon$) characteristics of fiber reinforced concrete in the uniaxial tension test. Results from an experimental parametric study involving used fiber quantity, type, and mechanical properties in the uniaxial tension test are presented and discussed.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.201-205
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• 2000

Fiber reinforced plastic (FRP) composites and ceramic matrix composites (CMC) which contain electrically conductive phases have been designed and fabricated to introduce the detection capability of damage/fracture detection into these materials. The composites were made electrically conductive by adding carbon and TiN particles into FRP and CMC, respectively. The resistance of the conductive FRP containing carbon particles showed almost linear response to strain and high sensitivity over a wide range of strains. After each load-unload cycle the FRP retained a residual resistance, which increased with applied maximum stress or strain. The FRP with carbon particles embedded in cement (mortar) specimens enabled micro-crack formation and propagation in the mortar to be detected in situ. The CMC materials exhibited not only sensitive response to the applied strain but also an increase in resistance with increasing number of load-unload cycles during cyclic load testing. These results show that it is possible to use these composites to detect and/or fracture in structural materials, which are required to monitor the healthiness or safety in industrial applications and public constructions.

• 대한토목학회논문집
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• 제26권4D호
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• pp.601-608
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• 2006

포장을 설계하고 설계 수명을 산정하거나 현재 공용중인 포장의 유지 관리를 위한 상태 평가를 수행해야하는 경우 포장의 거동 분석은 중요한 입력 변수로 작용하게 된다. 포장의 거동을 예측하기 위해서는 정확한 타이어의 접지면적과 타이어의 압력이 필요하다. 따라서 본 연구에서는 실제 측정된 타이어의 형상을 측정하여 PCA에서 제안한 타이어의 형상과 비교하고, 측정된 타이어의 접지면적과 타이어의 종류에 대한 타이어 압력분포를 사용하여 3차원 유한요소해석을 통하여 포장의 거동을 예측하고 예측된 포장의 거동과 실제 포장의 거동을 비교 분석하였다. 해석 결과 표층의 경우 타이어의 형상과 비선형 압력분포의 영향을 크게 받으며, 이러한 타이어의 특성을 고려함으로써 현장 거동을 보다 잘 설명할 수 있는 것으로 나타났다. 하지만 중간층의 경우 타이어의 영향이 크지 않은 것으로 나타났으며, 실제 현장 거동과 비교했을 때 타이어 하부에서는 큰 차이를 보여주어 실제 포장의 거동을 보다 정확하게 예측하기 위해서는 이 부분을 보다 명확하게 설명을 할 수 있어야 할 것으로 나타났다.