• 대한기계학회논문집A
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• 제32권5호
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• pp.387-395
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• 2008

Stress distribution and interfacial debonding process at the interface between a rubber mold and a powder compact were analyzed during unloading under cold isostatic pressing. The Cap model proposed by Lee and Kim was used for densification behavior of powder based on the parameters involved in the yield function of general Cap model and volumetric strain evolution. Cohesive elements incorporating a bilinear cohesive zone model were also used to simulate interfacial debonding process. The Cap model and the cohesive zone model were implemented into a finite element program (ABAQUS). Densification behavior of powder was investigated under various interface conditions between a rubber mold and a powder compact during loading. The residual tensile stress at the interface was investigated for rubber molds with various elastic moduli under perfect bonding condition. The variations of the elastic energy density of a rubber mold and the maximum principal stress of a powder compact were calculated for several interfacial strengths at the interface during unloading.

• 한국농공학회지
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• 제34권4호
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• pp.69-79
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• 1992

To estimate soil behavior and structural characteristics under the conditions of cyclic loading, freezing & thawing and initial state, several testing was performed and obtained following results. 1.After repeated freezing and thawing processes, original soil structure was destroyed and changed to globular structure from honeycomb or tube in its structure types. Also above processes resulted increasing the soil compression strain while decreasing the failure stress in stress-strain relationship and reached the soil structure into the mode of brittle fracture. Under cyclic loading conditions, soil cluster which was originally dispersed structure colloided with each other, seperated, and finally the soil failed due to the effect of overcompaction. 2.Through the stabilization processes seperated by four steps, the structure of soil skeleton was changed to quite different globular type. The degree of compressibility of soil was decreased in the normally consolidated zone, while the strength against external load increased due to soil particle stabilization. 3.Soil stress-strain chracteristics were largely influenced by repeated up and down processes of temperature. The maximum deformation was obtained in the case of temperature between 0 10˚C by the reseon of particle cluster reformation. 4.Soil compressibility was largely influenced by the optimum moisture content. Under freezing process, swelling could be found and its magnitude was proportional to the density of soil. 5.Density of soil was decreased as increasing the number or repeated freezing and thawing processes and the largest decreasing rate was found at the first turning point from freezing to thawing cycle.

• Design & Manufacturing
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• 제15권2호
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• pp.23-29
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• 2021

The specific strength of magnesium alloy is four times that of iron and 1.5 times that of aluminum. For this reason, its use is increasing in the transportation industry which is promoting weight reduction. At room temperature, magnesium alloy has low formability due to Hexagonal closed packed (HCP) structure with relatively little slip plane. However, as the molding temperature increases, the formability of the magnesium alloy is greatly improved due to the activation of other additional slip systems, and the flow stress and elongation vary greatly depending on the temperature. In addition, magnesium alloys exhibit asymmetrical behavior, which is different from tensile and compression behavior. In this study, a jig was developed that can measure the plane deformation behavior on the surface of a material in tensile and compression tests of magnesium alloys in warm temperature. A jig was designed to prevent buckling occurring in the compression test by applying a certain pressure to apply it to the tensile and compression tests. And the tensile and compressive behavior of magnesium at each temperature was investigated with the developed jig and DIC equipment. In each experiment, the strain rate condition was set to a quasi-static strain rate of 0.01/s. The transformation temperature is room temperature, 100℃. 150℃, 200℃, 250℃. As a result of the experiment, the flow stress tended to decrease as the temperature increased. The maximum stress decreased by 60% at 250 degrees compared to room temperature. Particularly, work softening occurred above 150 degrees, which is the recrystallization temperature of the magnesium alloy. The elongation also tended to increase as the deformation temperature increased and increased by 60% at 250 degrees compared to room temperature. In the compression experiment, it was confirmed that the maximum stress decreased as the temperature increased.

• 대한기계학회논문집A
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• 제40권6호
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• pp.531-537
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• 2016

기계 혹은 구조물의 파손 및 파괴는 소재의 내부에 존재하는 결함에서 발생하는 크랙에 의한 것이다. 이러한 크랙들은 밀집하여 존재하는 경우가 많기 때문에 크랙의 진전 및 성장특성들을 고려하지 않으면 안 된다. 이에 따라 본 연구에서는 표준 CT 시험편 내부의 크랙 및 구멍의 위치에 따른 파괴특성을 고찰하였으며, 표준CT 시험편에 편심된 집중하중을 가하였을 때, 시험편 내 크랙 주변의 구멍의 존재유무 및 위치에 따른 파괴역학적 거동에 대하여 규명하였다. 연구 결과로서 Model 3(크랙 주변에 구멍이 한 개 존재하는 시험편 모델로서 크랙의 끝부분과 구멍 간의 거리 가로방향으로 2mm의 경우)가 최대 변형량, 최대 응력 및 최대 변형 에너지, 모두 가장 크게 나타났으며, 모든 시험편 모델들이 시험편 내부의 크랙과 구멍의 거리가 가까울수록 최대 응력이 커지는 경향을 보였다. 또한 구멍의 개수와는 별개로 시험편 내부의 크랙 가까이에 구멍이 존재할 때 크랙 가까이에서 최대 응력은 커지는 경향이 나타나는 것을 알 수 있었으며, 이러한 본 연구 결과를 토대로 기계 혹은 기계 구조물 내부에 구멍을 뚫는다면, 시험편에 발생하는 파괴 응력의 값을 줄임으로써 파손이나 고장이 일어나는 것을 방지할 수 있을 것으로 사료된다.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.245-256
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• 2019

The experimentally determined mechanical behavior of the material under the prescribed service conditions is the basis of advanced engineering optimum design. To allow experimental data on the behavior of the material considered, uniaxial stress tests were made. The aforementioned tests have enabled the determination of mechanical properties of material at different temperatures, then, the material's resistance to creep at various temperatures and stress levels, and finally, insight into the uniaxial high cyclic fatigue of the material under different applied stresses for prescribed stress ratio. Based on fatigue tests, using modified staircase method, fatigue limit was determined. All these data contributes the reliability of the use of material in mechanical structures. Data representing mechanical properties are shown in the form of engineering stress-strain diagrams; creep behavior is displayed in the form of creep curves while fatigue of the material is presented in the form of S-N (maximum applied stress versus number of the cycles to failure) curve. Material under consideration was 18CrNi8 (1.5920) steel. Ultimate tensile strength and yield strength at room temperature and at temperature of $600^{\circ}C$: [${\sigma}_{m,20/600}=(613/156)MPa$; ${\sigma}_{0.2,20/600}=(458/141)MPa$], as well as endurance (fatigue) limit at room temperature and stress ratio of R = -1 : (${\sigma}_{f,20,R=-1}=285.1MPa$).

• 농업과학연구
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• 제39권1호
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• pp.97-110
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• 2012

This study was carried out for safety evaluation, the practical application and improvement of design method of the agricultural reservoir embankment according to backside extension. Seepage analysis, slope stability analysis and finite element analysis were performed for steady state and transient conditions. Also, the pore water pressure, seepage quantity, safety factor and stress-strain behavior according to high water level and rapid drawdown were compared and analyzed. The pore water pressure at contact region between backside extension and old embankment was kept high after rapid drawdown. Therefore, backside extension is recommended that design method is required to be improved and reinforced more than the others raising embankment. The hydraulic gradients before and after backside extension showed high value at the base of the core, but they showed stable state at the upstream slope and downstream slope. The seepage quantity per 1 day and the leakage per 100 m for the steady state and transient conditions appeared to be safe against the piping. The safety factor of slope stability showed high at the steady state, and transient conditions did not show differences depending on the rapid drawdown. The safety factor was appeared high at the upstream slope before backside extension and downstream slope after extension. The excess pore water pressure for steady state and transient conditions showed negative(-) at the upstream slope, it was small at the downstream slope. The mean effective stress (p') showed high at the base of the core and to be wild distribution after the extension. The displacement after extension showed 0.02-0.06 m in the upstream slope, the maximum shear strain after extension was smaller than that before extension.

• 한국전산구조공학회논문집
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• 제23권2호
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• pp.191-198
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• 2010

이 연구에서는 접착패치보강의 서로 다른 형태 즉, 패치와 접착제의 재료, 크기, 두께 뿐만 아니라 일면보강 또는 양면보강에 따른 일변균열판의 응력감소에 대한 연구가 수행되었다. 수치해석 도구로는 p-수렴 부분층별 모델이 사용되었다. 이 모델의 면내 변위는 구간별 연속인 선형변화로 가정하였고, 두께방향으로의 면외 변위는 일정한 상수로 가정하여 적용하였다. 변위장의 정의는 적분형 르장드르 다항식을 적용하였고, 수치적분은 별도의 외삽법 없이 각 층별의 절점에서 발생하는 적분값을 바로 얻을 수 있는 가우스-로바토 적분법을 사용 하였다. 또, 에너지 방출률법을 사용하여 응력확대계수를 산출하였다. 수치예제를 통해 제안된 모델의 정확도는 물론이고 접착패치 보강형태에 따라 변화되는 무차원 응력확대계수와 처짐의 항으로 응력감소 효과를 분석하였다.

• 한국주조공학회지
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• 제37권6호
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• pp.199-206
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• 2017

In this study, the variations of microstructures and tensile properties of Ti-(44-54)at.%Al binary alloys were investigated. The heat-treated microstructure depended greatly on their solidification structure and annealing temperature. We measured the variations of volume fractions of primary and secondary lamellar structure as a function of the heat treatment temperature in a Ti-47at.%Al alloy. The variation of ductility as a function of Al content was in good agreement with the change of fracture mode in the tensile fracture surface. It can be inferred that the variations of yield stress and hardness of ${\gamma}$ phase in a single ${\gamma}$-phase field region are enhanced by anti-site defects created by deviations from the stoichiometric composition. In a Ti-47at.%Al alloy within the (${\alpha}_2+{\gamma}$) two-phase field, the yield stress tended to be the maximum at a near equal volume fraction of lamellar and ${\gamma}$ grains. The ductility depended sensitively on the overall grain size and Al content. The calculation of fracture strain using Chan's model indicated that the change of ductility as a function of annealing temperature was primarily determined by the variations in the overall grain size and lamellar volume fraction.

• 지질공학
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• 제32권1호
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• pp.13-26
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• 2022

본 연구는 방해석 내 쌍정을 이용하여 조선누층군 풍촌석회암층의 고응력장을 규명하기 위함이다. 이를 위해 조선누층군 두위봉형의 풍촌석회암에서 6개의 시료를 채취하여 방해석 c-축의 방향 및 경사, e 쌍정면의 방향 및 경사, 쌍정의 평균 두께 및 갯수, 방해석 입자의 크기 등을 측정하였다. 측정된 자료들은 Calcite Strain Gauge 프로그램에 입력되어 쌍정의 변형률, 평균 두께, 치밀도 및 고응력장의 상대적 크기 및 방향 등을 계산하였다. 쌍정의 변형률은 1.09~15.36%, 평균 두께는 0.53~3.72 ㎛, 치밀도는 21.0~53.1 twin/mm의 범위를 보인다. 쌍정의 변형률, 치밀도 및 두께에 의한 변성온도 계산결과 대부분의 시료에서 170~200℃ 이하를 보여, 풍촌층의 상부층인 직운산층의 변성온도에 비교할 때 최대 심도의 절반 이상 상승한 후에 쌍정이 생성된 것으로 판단된다. 응력장의 방향은 5개의 시료에서 2방향을 보이는 반면, 단지 1개의 시료에서만 한 방향을 보여 대부분의 시료에서 압축응력이 2번 이상 작용하였음을 보여준다. 압축응력은 WNW-ESE~ENE-WSW의 방향성이 가장 우세하고 NW-SE와 NE-SW의 방향성도 보인다. 본 연구에서 측정된 고응력장과 연구지역 인근에서 지질구조나 다른 방법에 의하여 규명된 고응력장과 비교할 때 E-W 방향의 고응력장은 트라이아스기 말에서 쥬라기 초에 발생한 송림조산운동에 가장 큰 압축응력이 작용하였고 쥬라기에 발생한 대보조산운동과 불국사 변동에 의해서도 쌍정이 생성된 것으로 판단된다.

• 한국농공학회논문집
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• 제64권3호
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• pp.45-52
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• 2022

Prediction of soil behavior should be interpreted based on the level of axial strain in the actual ground. Recently numerical methods have been carried out focus on the state of soil failure. However considered the deformation of soil the prior to failure, mostly the small strain occurring in the elastic range is considered. As a result of calculating the deformation modulus to 50% of the maximum unconfined compression strength, Deformation modulus (E50) showed a tendency to increase according to the degree of compaction by region. The Poisson's ratio during loading-unloading was 0.63, which was higher than the literature value of 0.5. For the unconfined compression test under cyclic loading for the measurement of permanent strain, the maximum compression strength was divided into four step and the test was performed by load step. Changes in permanent strain and deformation modulus were checked by the loading-unloading test for each stage. At 90% compaction, the permanent deformation of the SM sample was 0.21 mm, 0.37 mm, 0.6 mm, and 1.35 mm. The SC samples were 0.1 mm, 0.17 mm, 0.42 mm, and 1.66 mm, and the ML samples were 0.48 mm, 0.95 mm, 1.30 mm, and 1.68 mm.