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

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.433-439
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• 2005

This paper describes a reinforced concrete crack model, which utilizes a strain decomposition technique. The strain decomposition technique enables the explicit inclusion of physical behavior across the cracked concrete surface such as aggregate interlock and dowel action rather than intuitively defining the shear retention factor. The proposed concrete crack model is integrated into the commercial finite element software ABAQUS shell elements through a user-supplied material subroutine. The FE results have been compared to experimental results reported by other researchers. The proposed bridge FE model is capable of predicting the initial cracking load level, the ultimate load capacity, and the crack pattern with good accuracy.

• Steel and Composite Structures
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• 재36권6호
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• pp.631-642
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• 2020

This paper studies nonlinear stability behavior of a nanocrystalline silicon curved nanoshell considering strain gradient size-dependency. Nanocrystallines are composite materials with an interface phase and randomly distributed nano-size grains and pores. Imperfectness of the curved nanoshell has been defined based on an initial deflection. The formulation of nanocrystalline nanoshell has been established by thin shell theory and an analytical approach has been used in order to solve the buckling problem. For accurately describing the size effects related to nano-grains or nano-pores, their surface energies have been included. Nonlinear stability curves of the nanoshell are affected by the size of nano-grain, curvature radius and nano-pore volume fraction. It is found that increasing the nano-pore volume fraction results in lower buckling loads.

• 소성∙가공
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• 제8권1호
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• pp.101-107
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• 1999

The upset forging stage is the initial work in the forging process. It is used to remove the segregation and cavities of the ingot. Specially in handling large sized ingot, an improper upset forging can cause serious surface tearing. However, there is no detail reference for stable upset forging work. To resolve this difficulty, we studied several factors such as upset forging time, temperature varation of ingot, damage, load and stain rate etc., by using the rigid-plastic finite element approach available in the DEFORM code. Numerical simulation results indicated that: the load value of upset forging works shows severe decreasing trend at a certain point, same as strain rate. Also defects were found to be concentrated around the upper and lower portions of the ingot. With these results, we can estimate a guideline for stable upset forging work.

• 소성∙가공
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• 제17권7호
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• pp.517-522
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• 2008

A visco-plastic self-consistent (VPSC) polycrystal model has been applied to simulate texture simulation and anisotropic properties of DP steels during deep drawing process. In order to evaluate the strain path during deep drawing, a steady state was assumed in the flange part of deep drawn cup. The final stable orientations were strongly dependent on the initial location in the blank. The evolution of anisotropy of DP steel sheets has been demonstrated through comparison of plastic strain rate vector at the different plastic strain levels.

• KSBB Journal
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• 제13권5호
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• pp.518-523
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• 1998

A large quantity of ethylene glycol(EG) is remained in the effluent after pretreating polyester weight-loss wastewater physicochemically in the fist stage and must be treated biologically in the second stage. Therefore, an excellent EG-utilizing bacteria strain was isolated from the natural system and the optimal culture conditions of the strain were investigated. The optimal culture conditions of temperature, pH, and nitrogen source were found to be 35$^{\circ}C$, 7.5 and ammonium chloride, respectively, when CODCr removal efficiency was more than 90%. The growth of stains and EG removal efficiency was slightly improved by adding elements such as niacin and biotin. With increasing inoculation size in a batch culture, the removal efficiency of EG was conspicuously increased. Growth rate was inhibited when the initial concentration of EG was more then 30g/L. The strain was identified as Pseudomonas sp. based on morphological and biological characteristics and named as Pseudomonas sp. EG1.

• 한국연초학회지
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• 제10권1호
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• pp.57-63
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• 1988

The mutagenic activities of the pyrolysates(300, 600, 750 and 85$0^{\circ}C$) of extracts from four antitussive or expectorant medicinal plants(Daturae Folios, Scopoliae Rhizoma, Acori Rhisoma, and Schigandrae Fructus) were studied in the Ames Salmonella/microsomes test system. The pyrolyzate of Schizandrae Fructus did not show the mutagenicity to tester strain TA98 of Salmonella typhinurium. However, those of other medicinal Plants, Daturae Folium, Scopoliae Rhigoma and Acori Rhizoma, exhibited the mutagenic activity to this strain and the mutagenicity of them were decreased gradually to 70% of the initial activity according to time course after the preparation of the samples with DMSO.

• Journal of Microbiology and Biotechnology
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• 제4권1호
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• pp.56-62
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• 1994

A yeast strain, BT001, which can directly ferment D-xylose to ethanol was isolated from forest soils, and then identified as Candida sp. Cultural conditions for the optimum ethanol production, along with the effects of aeration on cell growth and ethanol production were investigated. Aeration stimulated the cell growth and the volumetric rate of ethanol production, but decreased the ethanol yield. Optimum temperature and initial pH for the ethanol production were $33{\circ}^C$ and 6.0, respectively. In a shake flask culture, this strain produced 52.3 g ethanol per liter from 12%(w/v) D-xylose after incubation for 96 hours. Ethanol yield was 0.436 g per g D-xylose consumed. This corresponds to 85.8% of theoretical yield. Also, this yeast strain produced ethanol from D-galactose, D-glucose and D-mannose, but not from L-arabinose and L-rhamnose. Among these sugars, D-glucose was the fastest in being converted to ethanol sugars.

• 한국자동차공학회논문집
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• 제12권3호
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• pp.139-144
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• 2004

Dynamic crack initiation in ductile steel is investigated by means of impact loaded 3 point bend(PB) specimens. Results from non-viscoplastic and viscoplastic materials are compared. Their materials are applied with various impact velocities and static strain rates. The specimen has the size 320${\times}$750 mm with a thickness of 10 mm. A modified 3PB specimen design with reduced width at the ends has been developed in order to avoid the initial compressive load of the crack tip and also to avoid the uncertain boundary conditions at the impact heads. Numerical simulations are made by using the FEM code ABAQUS. Therefore, their results are plotted by shapes of the von Mises plastic stress and equivalent plastic strain of the specimens applied by various impact velocities.

• Geomechanics and Engineering
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• 제3권4호
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• pp.323-337
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• 2011

Israel's coastal region consists, mainly, of Pleistocene and Holocene sands with varying degrees of calcareous cementation, known locally as "kurkar". Previous studies of these materials emphasized the difficulty in their geotechnical characterization, due to their extreme variability. Consequently, it is difficult to estimate construction stability, displacements and deformations on, or within these soils. It is suggested that SPT and Menard pressuremeter tests may be used to characterize the properties of these materials. Values of elastic modulus obtained from pressuremeter tests may be used for displacement analyses at different strain levels, while accounting for the geometric dimensions (length/diameter ratio) of the test probe. A relationship was obtained between pressuremeter modulus and SPT blow count, consistent with published data for footing settlements on granular soils. Cohesion values, for a known friction angle, are estimated, by comparing field pressuremeter curves to curves from numerical (finite element or finite difference) analyses. The material analyzed in the paper is shown to be strain-softening, with the initial cohesion degrading to zero on development of plastic shear strains.