• 소성∙가공
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• 제9권6호
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• pp.615-623
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• 2000

The industrial application of hydroforming has a great potential in saying cost and achieving dimensional accuracy in automotive industry presently. The aim of the following article is to investigate the effect of process parameters on hydroformed part. Firstly, we have to investigate the change of mechanical properties for sheet and pipe material according to various radius/thickness ratio(r/t). The change of mechanical properties affects the yield stress more than the total elongation. Increase of yield stress for pipe has a bad influence on formability of hydroforming. Among the roll-forming process, the sizing process didn't change mechanical properties. The process parameters such as the initial pressure, mandrel shape and friction have seriously influenced on formability of hydroforming. Therefore we need to check formability of given material through the FE analysis in the beginning stage of process design and the predicted hydroforming process parameters ate generally a good starting point for the prototype tryout stage. The results of pretending, hydroforming analysis using FE model are good agreement with experimental results.

• 대한기계학회논문집
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• 제19권9호
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• pp.2071-2081
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• 1995

In order to examine the effects of yield stress, tensile strength and thickness on the buckling behavior during bending of pipes, the nonlinear finite element analysis of the 3-point bending tests was carried out using the commercial software (ABAQUS) under the condition of L4(2$^{3}$) performed according to the designed condition. Form the analysis of simulation results, it was found that yield stress and thickness were the major factors on buckling load at pipe bending and tensile strength gave little influence because the plastic strain and plastic zone are small. For the punch displacement to the occurrence of buckling, thickness is a major factor and yield stress and tensile strength are the minor factors.

• 한국농공학회지
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• 제27권1호
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• pp.37-45
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• 1985

To define the amount of consumptive use of upland crops, the moisture consumption characters were investigated with different soil moisture content by soil properties(loam, sandy loam, sand) at the experimental farm of Kon-Kuk University from April 20 to July 20 1984. The results obtained are summarized as follows; 1. Total moisture consumption under bare soil condition had an order of loam> sandy loam> sand and showed an order of pF 1.5> pF2. 1> pF 2.7 by re-irrigation point and the average during the experimental period (92days) was 435. 9mm and the daily average moisture consumption was 4. 7mm. 2. The moisture consumption characters of bare soil plot obtained showed that the amount of irrigation water per one time and the days of intermission increased and, on the contrary, the times of irrigation and the total amount of irrigation water decreased by the increment of re-irrigation point in the same soil 3. Total moisture consumption of spring cabbage under open cultivation showed 528.6 rim in maximum and had an order of loam> sandy loam> sand. In the aspect of rc-irrigation point, it had an order of pFl. 5> pF 2.1> pF 2.7. In case the planning basic year was taken into account, the amount of irrigation water needed for open cultivation was 456. 3 mm and its average daily moisture consumption was 6. 2mm. 4. Total moisture consumption of summer cucumber under open cultivation showed 635. 8mm in maximum and had an order of loam> sandy loam> sand. In the aspect of re-irrigation point, it had an order of pF 1.5> pF2. 1> pF2. 7 In case the planning basic year was taken into consideration, the amount of irrigation water was 516. 9mm and its aversge daily moisture consumption was 6. 5mm. 5. The result of cabbage cultivation showed its maximum yield in loam soil when the pF values were maintained from 1,5 to 2.1 and then the evapotranspiration ratio was 1, 76 and also when the amount of irrigation water were similar, it showed effective to reduce the days of intermtission. 6. The result of cucumber cultivation showed its maximum yield in sandy loam soil when the pF value maintained from 1.5 to 1.7 and when the irrigation point maintained at pF 2,7 in sandy soil, its yield was severely decreased.

• 한국농공학회지
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• 제45권5호
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• pp.85-96
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• 2003

The Revised Universal Soil Loss Equation (RUSLE) has been used in over 100 countries to estimate potential long-term soil erosion from the field. However, the RUSLE estimated soil erosion cannot be used to estimate the sediment delivered to the stream networks. For an effective erosion control, it is necessary to compute sediment delivery ratio (SDR) for watershed and sediment yield at watershed outlet. Thus, the Sediment Assessment Tool for Effective Erosion Control (SATEEC) was developed in this study to compute the sediment yield at any point in the watershed. To compute spatially distributed sediment yield map, the RUSLE was first integrated with the ArcView GIS and three area based sediment delivery ratio methods were incorporated in the SATEEC. The SATEEC was applied to the Bangdong watershed, Chuncheon, Gangwon Province to demonstrate how it can be used to estimate soil loss and sediment yield for a watershed. The sediment yield using USDA SDR method is 8,544 ton/year and 4,949 ton/year with the method by Boyce. Thus, use of watershed specific SDR is highly recommended when comparing the estimated sediment yield with the measured sediment data. The SATEEC was applied with hypothetical cropping scenario and it was found that the SATEEC can be used to assess the impacts of different management on the sediment delivered to the stream networks and to find the sediment source areas for a reach of interest. The SATEEC is an efficient tool to find the best erosion control practices with its easy-to-use interface.

• Composites Research
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• 제36권5호
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• pp.369-376
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• 2023

본 연구에서는 복합소재의 기지재로 활용되고 있는 에폭시 고분자의 가교율이 항복표면에 미치는 영향을 분자동역학 해석을 통해 평가하고자 한다. 분자동역학 해석을 활용하여 가교율에 따른 에폭시 모델을 형성한 후, 상온-대기압 조건하에서 단축 변형 해석 및 평면응력 조건을 고려한 다축 변형 해석을 수행하였으며, 해석 데이터를 통하여 가교율에 따른 영률, 항복점, 항복표면, 그리고 경화지수를 도출하였다. 해석 결과, 영률 및 응력은 기존 선행 연구들에서 조사되었듯이, 가교율에 따라 증가하는 경향을 확인하였다. 다축 변형 시에는, 이러한 가교율과 도출된 응력간의 관계가 하중의 방향에 따라 의존적임을 확인하였는데, 가교율이 증가할수록 단축 인장 영역에 비해, 이축 압축 영역의 항복표면은 빠른 속도 팽창하였으며, 이로 인한 항복표면의 상이함을 관측하였다. 이를 통해, 고분자 소재의 항복 표면의 압력의존성은 소재의 가교 정도에 의존적이며, 항복이 진행될수록, 압력의 존성은 동일 소재 하에서도 변할 수 있음을 확인하였다.

• 한국초지조사료학회지
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• 제13권2호
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• pp.132-138
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• 1993

Yield and plant constituent responses of forage sorghum cultivars have usually been compared in uniform defoliation management test. However the influence of harvest time on differential response of cultivars needs more precise definition. Therefore this study with sorghum-sorgo-sudan hybrid cv. NC+Sweet Leaf, and Super Su 22 and Sorghum-Sorghum hybrid cv. Pioneer 931 was carried out under two defoliation regimes, namely defoliation at heading stage of each variety and defoliation on the same calendar date in response to heading stage of early variety. The results are summarized as follows; 1. Three harvests were taken by early variety with 80 days and two harvests by late variety with 94 days from sowing to heading. 2. Dry matter and TDN yield tend to be higher when the plants are cut at ear emergence stage of late variety. 3. Crude protein content was similar for the same growth growth stage of 1st growth and 1st regrowth, and rather big different between varieties. 4. Considering only dry matter and TDN yield, it is recommendable to cut two times at ear emergence stage of late variety and also three times at ear emergence stage of early variety in view point of utilization period extension and distribution of forage products.

• 대한기계학회논문집A
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• 제28권5호
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• pp.554-562
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• 2004

An empirical relationship between parameters from SP curves and tensile properties has been systematically investigated by experimental tests and FEM simulations. A series of SP and tensile tests were performed. SP tests were also simulated by FE analysis with various tensile properties. It was found that the yield loads(Py) and the maximum loads( $P_{MAX}$) in SP curves were linearly related with the yield strength($\sigma$$_{o}$) and the tensile strength($\sigma$$_{UTS}$), respectively. The yield loads defined from the intersection point of two lines tangent to the elastic bending region and plastic bending region showed better relation to the yield strength than those from offset line. The maximum loads in SP curves showing plastic instability region was linearly related with the tensile strengths. The slope of SP curves in simulation results had a close correlation with the hardening coefficient and hardening strength as well.l.l.l.

• Advances in Computational Design
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• 제9권1호
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• pp.39-52
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• 2024

If the governing differential equation arising from engineering problems is treated as an analytic, continuous and derivable function, it can be expanded by one point as a series of finite numbers. For the function to be zero for each value of its domain, the coefficients of each term of the same power must be zero. This results in a recursive relationship which, after applying the natural conditions or the boundary conditions, makes it possible to obtain the values of the derivatives of the function with acceptable accuracy. The elastoplastic analysis of an inhomogeneous thick sphere of metallic materials with linear variation of the modulus of elasticity, yield stress and Poisson's ratio as a function of radius subjected to internal pressure is presented. The Beltrami-Michell equation is established by combining equilibrium, compatibility and constitutive equations. Assuming axisymmetric conditions, the spherical coordinate parameters can be used as principal stress axes. Since there is no analytical solution, the natural boundary conditions are applied and the governing equations are solved using a proposed new method. The maximum effective stress of the von Mises yield criterion occurs at the inner surface; therefore, the negative sign of the linear yield stress gradation parameter should be considered to calculate the optimal yield pressure. The numerical examples are performed and the plots of the numerical results are presented. The validation of the numerical results is observed by modeling the elastoplastic heterogeneous thick sphere as a pressurized multilayer composite reservoir in Abaqus software. The subroutine USDFLD was additionally written to model the continuous gradation of the material.

• 한국구조물진단유지관리공학회 논문집
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• 제26권6호
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• pp.47-53
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• 2022

콘크리트구조물의 한계상태설계법이 적용되면서 구조물의 극한상태까지 고려하는 설계가 이루어지고 있다. 실제 철근콘크리트 부재가 인장력을 부담할 때 부재가 항복한 후에도 극한상태까지 콘크리트가 인장력을 부담한다. 따라서 한계상태 거동에 대한 정확한 평가를 위해서는 휨 부재의 항복 후 인장강화효과에 대한 연구가 필요하다. 본 연구에서는 복철근 직사각형 단면을 가지는 RC 단순보에 대하여 4점 휨 실험을 수행하였고, 영상분석기법을 이용하여 부재의 거동을 상세하게 분석하였다. 분석 결과를 이용하여 휨 인장강화효과 계수를 도입한 항복 후 인장강화효과 추정식을 제안하였고, 이를 기존 연구들의 실험 결과를 통해 적용성을 검증하였다. 부재의 연성거동을 대표하는 극한 변형률과 항복 변형률 차이가 실험 결과와 유사하게 나타나 제안식의 예측이 비교적 정확한 것으로 판단된다.

• 분석과학
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• 제5권4호
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• pp.373-379
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• 1992

피난의 열 이성화반응 생성물에 관한 연구를 위하여 열분해 조건을 가스크로마토그래피와 질량분석기에 장치된 전기로형 및 curie-point 열분해기를 이용하여 실험을 행하였다. 그 결과, 최적 조건하에서 전기로형보다는 curie-point 열분해기에 의해서 피난으로부터 주 이성화 생성물인 citronellen (70%)을 얻었다. 본 연구에서 열분해 최적 조건은 $590^{\circ}C$, 4 Sec이고, 확인된 열분해 주 생성물은 citronellene, m-Menth-6-ene, m-Menth-1-ene, 1-Methyl-4(1-methyl-ethylidene) cyclohexane이었다.