• Title/Summary/Keyword: 체적변형률

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A Constitutive Model for Rotation of Principal Stress Axes during Direct Simple Shear Deformation (직접단순전단변형에 따른 주응력 방향의 회전을 고려한 구성모델)

  • Park, Sung-Sik;Lee, Jong-Cheon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.1C
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    • pp.53-62
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    • 2008
  • A constitutive model, which can simulate the effect of principal stress rotation associated with direct simple shear test, is proposed in this study. The model is based on two mobilized planes. The plastic strains occur from the two mobilized planes, and depend on stress state, and they are added. The first plane is a plane of maximum shear stress, which rotates about the horizontal axis, and the second plane is a horizontal plane which is spatially fixed. The second plane is used to consider the effect of principal stress rotation on simple shear tests under different stress states. The soil skeleton behavior observed in drained simple shear tests is captured in the model. This constitutive model is incorporated into the dynamic coupled stress-flow finite difference program FLAC. The model is first calibrated with drained simple shear tests on loose Fraser River sand. The measured shear stress and volume change are partially induced by principal stress rotation and compared with model calculations. The model is verified by comparing predicted and measured settlements due to rigid footing resting on loose sands. Settlements predicted by the proposed model were very similar to measured settlements. Mohr-Coulomb model can not consider the effect of principal stress rotation and its prediction was only 20% of measured settlements.

A Study on the Behaviour of Baekma River Sands Using Elasto-Plastic Hyperbolic Model (탄·소성 쌍곡선 모델을 이용한 백마강 모래의 거동특성 연구)

  • Yang, Seung-Jae;Park, Ki-Hyeon;Park, Hyung-Yeol;Yang, Kyung-Jin;Kim, Chan-kee
    • Journal of the Korean Geosynthetics Society
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    • v.19 no.1
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    • pp.93-101
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    • 2020
  • In order to predict the nonlinear behaviour of the soil, the elasto-plastic hyperbolic model was selected, which was considered to be relatively simple and highly predictable. The soil parameter determination and the behavior analysis program were developed by formalizing the functions related to the constitutive model. Each soil parameter was determined from the results of the drained triaxial compression tests of Baekma river sand with the change of relative density. The stress-strain behavior was predicted using the soil parameters determined under each condition. As a result, the deviator stress for the axial strain is verified to have a good match between the measured value and predicted value at each relative density. In the relationship between the volumetric stain and the axial strain, when the relative density is loose, the measured value and predicted value tend to match, and when relative density is dense, the predicted value of the volumetric strain appears somewhat smaller than the measured value due to the limitation of the constitutive model.

Evaluation of Characteristics of Shear Strength and Poisso's Ratio through Triaxial and Bender Element Tests (벤더엘리먼트와 삼축시험을 통한 모래의 전단강도 및 포아송비 특성 규명)

  • Yoo, Jin-Kwon;Park, Du-Hee
    • Journal of the Korean Geotechnical Society
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    • v.30 no.5
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    • pp.67-75
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    • 2014
  • In this paper, isotropically consolidated drained triaxial compression test device installed with bender elements is used to measure stress, stain, and shear wave velocity, from which the characteristics of shear strength and Poisson'ratio are investigated. The results show that there is a unique relationship between maximum shear modulus determined from shear wave velocity and effective vertical stress at failure, which is defined as the sum of vertical and radial stresses at failure. The correlation is very useful since it is possible to predict the shear strength and internal friction angle from shear wave velocity. In addition, Poisson's ratio is determined from measured axial and volumetric strains. It is demonstrated that the range of measured Poisson's ratio is between 0.15 and 0.6, and increases with the axial strain. The ratios at axial strains smaller than 0.2% corresponds to the range recommended in design codes, which are approximately from 0.3~0.35. However, at axial strains exceeding 1%, the measured ratios are between 0.5 and 0.6. It is therefore shown that use of ratios commonly used in practice will result in pronounced underestimation at large strains.

Micro-mechanical Failure Prediction and Verification for Fiber Reinforced Composite Materials by Multi-scale Modeling Method (멀티스케일 모델링 기법을 이용한 섬유강화 복합재료의 미시역학적 파손예측 및 검증)

  • Kim, Myung-Jun;Park, Sung-Ho;Park, Jung-Sun;Lee, Woo-Il;Kim, Min-Sung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.41 no.1
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    • pp.17-24
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    • 2013
  • In this paper, a micro-mechanical failure prediction program is developed based on SIFT (Strain Invariant Failure Theory) by using the multi-scale modeling method for fiber-reinforced composite materials. And the failure analysis are performed for open-hole composite laminate specimen in order to verify the developed program. First of all, the critical strain invariants are obtained through the tensile tests for three types of specimens. Also, the matrices of strain amplification factors are determined through the finite element analysis for micro-mechanical model, RVE (Representative Volume Element). Finally, the microscopic failure analysis is performed for the open-hole composite laminate specimen model by applying a failure load obtained from tensile test, and the predicted failure indices are evaluated for verification of the developed program.

Stress Analysis in Multiple Isotropic Elliptical Fibers of Arbitrary Orientation (다수의 임의로 경사진 등방성 타원형 장섬유를 포함하는 복합재료에서의 응력 해석)

  • Lee, Jung-Ki;Oh, Sang-Min
    • Composites Research
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    • v.26 no.4
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    • pp.235-244
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    • 2013
  • A volume integral equation method (VIEM) is introduced for the solution of elastostatic problems in an unbounded isotropic elastic solid containing multiple isotropic elliptical fibers of arbitrary orientation subject to uniform stress at infinity. The fibers are assumed to be long parallel elliptical cylinders composed of isotropic elastic material perfectly bonded to the isotropic matrix. The solid is assumed to be under plane strain on the plane normal to the cylinders. A detailed analysis of the stress field at the matrix-fiber interface for square and hexagonal packing of the fibers is carried out for different values of the number, orientation angles and concentration of the elliptical fibers. The accuracy and efficiency of the method are examined through comparison with results obtained from analytical and finite element methods.

Analysis of Volumetric Deformation Influence Factor after Liquefaction of Sand using Cyclic Direct Simple Shear Tests (CDSS 실험을 이용한 모래의 액상화 후 체적변형 영향인자 분석)

  • Herrera, Diego;Kim, Jongkwan;Kwak, Tae-Young;Han, Jin-Tae
    • Journal of the Korean Geotechnical Society
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    • v.40 no.3
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    • pp.65-75
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    • 2024
  • This study investigates liquefaction-induced settlement through strain-controlled tests using a cyclic direct simple shear device on clean sand specimens. By focusing on the accumulated shear strain, soil density, sample preparation method, and cyclic waveshape, this study attempts to enhance the understanding of soil behavior under seismic loading and its further deformation. Results from tests conducted on remolded samples reveal insights into excess pore water pressure development and post-liquefaction volumetric strain behavior, with denser samples exhibiting lower volumetric strains than looser samples. Similarly, the correlation between the frequency and amplitude variations of the wave and volumetric strain highlights the importance of wave characteristics in soil response, with shear strain amplitude changes, varying the volumetric strain response after reconsolidation. In addition, samples prepared under moist conditions exhibit less volumetric strain than dry-reconstituted samples. Overall, the findings of this study are expected to contribute to predictive models to evaluate liquefaction-induced settlement.

A Characteristic of Deformation and Strength of Domestic Sands by Triaxial Compression Tests (삼축압축시험에 의한 국내 모래의 변형-강도 특성)

  • Park, Choon Sik;Kim, Jong Hwan;Park, Cheol Soo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.34 no.2
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    • pp.515-527
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    • 2014
  • This study conducted experiment for understanding engineering characteristics of domestic sands by examining standard sand and sand from Yokji Island and Nakdong River in terms of confining pressure, $K_0$, over consolidation and relative density factors through triaxial compression test. The test showed that deviator stress by strain positively changed as confining pressure and relative density grow while $K_0$ and over consolidation factors do not directly correlated with it. Angle of internal friction decreases as confining pressure increases which strengthens contact force between particles, and declines as relative density drops, whereas $K_0$ and over consolidation factors hardly affect the results. When it comes to volumetric strain, volume expansion decreases as confining pressure increase due to crushability and rearrangement of particles while $K_0$ and over consolidation shows same movement unconditionally, and relative density appears compressed as it grows at the beginning however it expands as axial strain increases. Modulus of elasticity ($E_{sec}$) by strain has tendency into convergence resulting in initial secant modulus of elasticity ($E_{ini}$) > secant modulus of elasticity($E_{sec}$) > tangent modulus of elasticity ($E_{tan}$). On the other hand, it grows as confining pressure and relative density increase while indicating similar modulus of elasticity ($E_{sec}$) regarding on $K_0$ and over consolidation. Slope of critical line (M) tended to decrease as confining pressure increases, follow same line according to $K_0$, confining pressure and relative density, and increase as relative density grows.

Constitutive Model for Hardening Materials such as Rock or Concrete (암석이나 콘크리트와 같은 경화재료에 대한 구성모델)

  • Kang, Byung Sun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.1
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    • pp.161-171
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    • 1993
  • The aim of this study is to provide the stress-strain behavior of hardening geological materials such as rock or concrete on three dimensional spaces by using Desai model based on plastic theory. To validate proposed model, truly triaxial tests with high pressure under variety of stress paths in which three principal stresses were controlled independently using concrete materials were performed. The main results are summerized as follows: 1. Various stress paths for hardening materials used are satisfactorily explained by performing the truly triaxial test with high pressure. This is very important to investigate constitutive equations for materials like rock or concrete. 2. Since the proposed yield function is continuous, it avoids the singularity point at the intersection of two function in the previous models, thus, reducing the difficulties for computer implementation. 3. Analytic predictions for yielding behavior on $J_1-{\sqrt{J_{2D}}}$ octahedral and triaxial plane, as well as volumetric strain and stress-strain behavior agree well with experimental results.

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Confinement Effects of High Strength Reinforced Concrete Tied Columns (고강도 철근콘크리트 띠철근 기둥의 구속효과)

  • 신성우;한범석
    • Journal of the Korea Concrete Institute
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    • v.14 no.4
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    • pp.578-588
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    • 2002
  • An experimental study was conducted to investigate the effectiveness of transverse reinforcement in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns(260$\times$260$\times$1200 mm) were tested. Effects of main variables such as the concrete compressive strength, the tie configuration, the transverse reinforcement ratio, the tie spacing, and the spatting of the concrete cover were considered. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse reinforcement that can provide sufficiently high lateral confinement pressure There is a consistent decrease in deformability of column specimen with increasing concrete strength. Test results were compared with the previous confinement model such as modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi model. The comparison indicates that many previous models for confined concrete overestimate or underestimate the ductility of confined concrete.

Effect of various surface roughness of steel sheet on characteristic of surface friction in stamping (판재의 표면 거칠기에 따른 표면 마찰 특성 변화)

  • 조상헌;허보영;아라이히로시;주상응;김상열;이용진;문만빈;이영수;고흥석
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2003.03a
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    • pp.24-24
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    • 2003
  • 최근 자동차 산업이 발달함에 따라 철강업계와 자동차 회사에서는 전에 많이 사용하던 내연 무도금강판 대신 부식에 저항력이 강한 도금강판을 사용한 이후로 냉연강판의 가공 시에 야기되지 않았던 많은 문제점들이 나타났다 자동차용 강판의 경우 판재의 체적에 비하여 금형과 판재의 접촉면적이 큰 프레스 공정에서는 판재의 표면에 작용하는 마찰력의 크기가 판재의 스탬핑 성형성에 큰 영향을 미친다. 이는 마찰특성이 비록 재료고유의 성형한계에서는 영향을 미치지 못하나 스탬핑 공정에 있어서 금형과의 접촉면에서 마찰력의 크기가 패널의 변형률분포를 변화시켜 스탬핑 성형성에 큰 영향을 주는 것이다. 따라서 본 연구는 자동차용 도금강판의 표면 거칠기에 따른 판재의 표면 마찰 특성 변화를 알아보았다. 소재의 기계적 특성 측정은 UTM을 사용하였고, 도금층은 XRD, SEM을 이용하여 상분석 하였으며, 표면 거칠기는 AFM(Atomic Force Microscope), SJ-400(Mitutoyo)을 사용하여 표면 거칠기를 측정하였다. 또 드로잉 하중을 비드부에서의 굽힘-굽힘 풀림 소성변형에 의한 변형력 성분과 마찰력 성분으로 분리하여 강판의 쿠롬 마찰계수를 DBS(Draw bead simulation)로 측정하였다.

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