• 제목/요약/키워드: critical relative density model

검색결과 19건 처리시간 0.022초

임계상대밀도 모델을 이용한 분말 등통로각압축 공정시 분말 치밀화 거동 (Analysis of Densification Behavior during Powder Equal Channel Angular Pressing using Critical Relative Density Model)

  • 복천희;유지훈;윤승채;김택수;천병선;김형섭
    • 한국분말재료학회지
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    • 제15권5호
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    • pp.365-370
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    • 2008
  • In this study, bottom-up powder processing and top-down severe plastic deformation processing approaches were combined in order to achieve both full density and grain refinement with least grain growth. The numerical modeling of the powder process requires the appropriate constitutive model for densification of the powder materials. The present research investigates the effect of representative powder yield function of the Shima-Oyane model and the critical relative density model. It was found that the critical relative density model is better than the Shima-Oyane model for powder densification behavior, especially for initial stage.

임계상대밀도모델을 이용한 마그네슘분말의 압출공정 치밀화 거동 (Analysis of Densification Behavior of Magnesium Powders in Extrusion using the Critical Relative Density Model)

  • 윤승채;채홍준;김택수;김형섭
    • 한국분말재료학회지
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    • 제16권1호
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    • pp.50-55
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    • 2009
  • Numerical simulations of the powder extrusion need an appropriate pressure-dependent constitutive model for densification modeling of the magnesium powders. The present research investigated the effect of representative powder yield function of the critical relative density model. We could obtain reasonable physical properties of pure magnesium powders using cold isostatic pressing. The proposed densification model was implemented into the finite element code. The finite element analysis was applied to simulation of powder extrusion of pure magnesium powder in order to investigate the densification and processing load at room temperature.

금속분말 혼합체의 압력의존 항복모델과 유한요소법을 이용한 금형압분 공정 시 고형화 해석 (Pressure-Dependent Yield Model for Metallic Powder Mixtures and Their Densification Behavior During Die Compaction as Analyzed by the Finite Element Method)

  • 윤승채;김택수;강승구;김형섭
    • 대한금속재료학회지
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    • 제47권9호
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    • pp.567-572
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    • 2009
  • The densification behaviors of mixtures of copper and steel powders during cold die compaction were investigated. We proposed the pressure-dependent yield function based on the rule of the mixtures of each yield function of a critical relative density type. The constitutive equations were implemented into a finite element program (DEFORM2D) to analyze the densification and deformation behavior of powder mixtures, and the simulated results are in good agreement with the experimental results in reference studies.

Numerical modeling of dynamic compaction process in dry sands considering critical distance from adjacent structures

  • Pourjenabia, Majid;Hamidi, Amir
    • Structural Engineering and Mechanics
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    • 제56권1호
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    • pp.49-56
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    • 2015
  • Dynamic compaction (DC) is a useful method for improvement of granular soils. The method is based on falling a tamper (weighting 5 to 40 ton) from the height of 15 to 30 meters on loose soil that results in stress distribution, vibration of soil particles and desirable compaction of the soil. Propagation of the waves during tamping affects adjacent structures and causes structural damage or loss of performance. Therefore, determination of the safe or critical distance from tamping point to prevent structural hazards is necessary. According to FHWA, the critical distance is defined as the limit of a particle velocity of 76 mm/s. In present study, the ABAQUS software was used for numerical modeling of DC process and determination of the safe distance based on particle velocity criterion. Different variables like alluvium depth, relative density, and impact energy were considered in finite element modeling. It was concluded that for alluvium depths less than 10 m, reflection of the body waves from lower boundaries back to the soil and resonance phenomenon increases the critical distance. However, the critical distance decreases for alluvium depths more than 10 m. Moreover, it was observed that relative density of the alluvium does not significantly influence the critical distance value.

실트질 해사의 역학적 특성 및 거동에 관한 연구 (Strength Characteristics and their Behaviours of Marine Silty Sands)

  • 장병욱;송창섭;우철웅
    • 한국농공학회지
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    • 제36권3호
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    • pp.74-83
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    • 1994
  • A series of isotropic consolidation tests, undrained and drained triaxial compression tests was carried out to investigate the physical characteristics and behaviours of marine silty sands collected from the western coast of Korea. This study also included a theoretical development of the constitutive equation to evaluate stress-strain relationship and volume change of silty sands. The results and main conclusions of the study are summarized as follows; 1. Isotropic compression and swelling index are linearly decreased with an increase in relative density. 2. Both undrained shear strengh and elastic modulus are increased with an increase in relative density and confining pressure. 3. Internal friction angles obtained from drained and undrained compression tests of the soils are proportional to relative density. 4. The phenomenon of dilatancy of each sample is less profound when confining stress is increased but more profound when relative density is increased. 5. The slope of critical state lines is 1.78 for Saemangum, 1.70 for Siewha and 1.26 for Sukmoon sands. 6. In this study, Drucker-Praper type criterion is used and hardening function of Cap model is modified by hyperbolic fuction. This will improve a lack of physical meaning of hardening parameters in conventional Cap model. 7. A newly developed constitutive equation to the forementioned silty sands and checked its applicability. This is in good agreement with the measured data.

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유한요소법을 이용한 등통로각압출 공정의 마그네슘 분말 고형화 거동 해석: 피복재 효과 (Finite Element Analysis of Densification of Mg Powders during Equal Channel Angular Pressing: Effect of Sheath)

  • 윤승채;김택수;김형섭
    • 한국분말재료학회지
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    • 제16권2호
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    • pp.85-90
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    • 2009
  • Magnesium and its alloys are attractive as light weight structural/functional materials for high performance application in automobile and electronics industries due to their superior physical properties. In order to obtain high quality products manufactured by the magnesium powders, it is important to control and understand the densification behavior of the powders. The effect of the sheath surrounding the magnesium powders on the plastic deformation and densification behavior during equal channel angular pressing was investigated in the study by experimental and the finite element methods. A modified version of Lee-Kim's plastic yield criterion, notably known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders. In addition, a new approach that extracts the mechanical characteristics of both the powder and the matrix was developed. The model was implemented into the finite element method, with which powder compaction under equal channel angular pressing was simulated.

모래지반에서 모형인장말뚝의 거동 (Behavior of Model Tension Piles in Sand)

  • 송영우
    • 한국지반공학회지:지반
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    • 제7권2호
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    • pp.5-26
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    • 1991
  • 지반의 상대밀도, 응력이력, 말뚝의 표면상태, 매설깊이 및 직경이 상양력을 받는 말뚝의 거동에 미치는 영향에 대한 모형실험결과가 발표되었다. 극한상양지지력은 모래의 상대밀도 뿐만아니라 현위치수평응력에 의존되며, 한계깊이 현상은 깊이에 따른 수평응력의 변화로 설명되고, Ktan 의 값은 말뚝직경의 증가함에 따라 감소하는 경향을 보인다.

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지하공동이 연속기초의 지지력에 미치는 영향 (Effects of the Bearing Capacity of Strip Footing by Underground Cavity)

  • 이준대;이봉직;오세욱;강종범
    • 한국안전학회지
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    • 제15권2호
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    • pp.111-117
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    • 2000
  • In this study, the bearing capacity behavior of strip footing located above a continuous cavity in sand was investigated experimentally. The model footing test was performed in a model box made by using raining method in sand. The model footing test results were compared with those obtained from theoretically proposed equations. The results of the analysis indicate that there is a critical region under the footing. For strip footing, there exists a critical depth below which the presence of the cavity has negligible influence on the footing performance. Only when the cavity is located within this region will the footing performance be significantly affected by the presence of the cavity. The size of the critical region depends on several factors such as footing shape, soil property, cavity size and cavity shape. When the cavity is located within the critical region, the bearing capacity of the footing varies with various factors, such as the size and location of the cavity and the depth of foundation. Based on the experimental study, the following conclusions were induced. 1. The ultimate bearing capacity due to the eccentricity of a underground cavity increases at the rate of the small rather than that due to the depth of a underground cavity. This indicates that the bearing capacity of a strip footing is influenced on the depth rather than the eccentricity of a underground cavity. 2. The critical $depth(D/B)_{cr}$, by underground cavity in sand soil ground that is made by the relative density($D_r$)=55%, 65%, 75%, approaches a range of about 8~10 in case of W/B=1, and about 11~13 in case of W/B=2. 3. In case of the relative density($D_r$) 75%, the most outstanding differential settlement trend is shown in the depth of 4~8cm regardless of the size of cavity, namely, when the value of D/B is 1~2. Therefore, a underground cavity influences on not only the decrease of the bearing capacity but also the differential settlement of a strip footing.

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폐경여성의 골다공증 예방행위 구조모형: 골밀도인지를 중심으로 (Structural Model for Osteoporosis Preventive Behaviors in Postmenopausal Women: Focused on their Own BMD Awareness)

  • 박영주;이숙자;신나미;강현철;김선행;김탁;전송이;조인해
    • 성인간호학회지
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    • 제25권5호
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    • pp.527-538
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    • 2013
  • Purpose: The purpose of this study was to develop a model that explains causal relationships between post-menopausal women's osteoporosis general knowledge and awareness of their own bone mass density(BMD) and their osteoporosis health beliefs and preventive behaviors. Methods: Retrospective design using structural equation model tested seven variables by using questionnaires of osteoporosis knowledge test, osteoporosis health belief scale, osteoporosis self-efficacy scale, and osteoporosis preventive behaviors scale. 162 middle age and post-menopausal women were recruited. Results: Mediating effect of health beliefs was not significant in the relationship between BMD awareness and preventive behaviors. Instead, BMD awareness had a direct influence on the preventive behaviors that is strong and significant. Between the relationship of the BMD awareness and health beliefs, direct pathways of perceived threat, relative benefits, and self-efficacy were not significant. However, relative benefits and self-efficacy showed direct influence on the preventive behaviors. Conclusion: Having middle age women get their BMD test done in order for them to be aware of their own BMD results might be a critical strategy to promote osteoporosis preventive behaviors. There is a need to develop diverse strategies to enhance their self-efficacy which has been shown to be important to osteoporosis preventive behaviors.

교대인접토체의 특성에 따른 강성저하를 고려한 교량시스템의 지진거동분석 (Dynamic Behaviors of a Bridge under Seismic Excitations Considering Stiffness Degradation with Various Abutment-Soil Conditions)

  • 김상효;마호성;경규혁;이상우
    • 한국전산구조공학회:학술대회논문집
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    • 한국전산구조공학회 2000년도 봄 학술발표회논문집
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    • pp.347-354
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    • 2000
  • The seismic behaviors of a bridge system with several simple spans are examined to see the effects of the longitudinal stiffness degradation due to abutment-soil interaction. The abutment-backfill system is modeled as one degree-of-freedom-system with nonlinear spring and linear damper. various soil-conditions surrounding the abutment such as loose sand, medium dense sand, and dense sand are considered in the bridge seismic analysis. The idealized mechanical model for the whole bridge system is modeled by adopting the multiple-degree-of-freedom system, which can consider components such as pounding phenomena, friction at the movable supports, rotational and translational motions of foundations, and the nonlinear pier motions. The stiffness of the abutment is found to be rapidly reduced at the beginning of the earthquakes, and to be converged to constant values shortly after the displacement approaches to the Predefined critical values. It is observed that the maximum relative distanced an maximum relative displacements are generally Increased as the relative density of a soil decreases As the peak ground acceleration increases, the response ratio of the case considering stiffness degradation to the case considering constant stiffness decreases.

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