• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.273-273
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• 2003

나노인덴테이션은 압자를 수 $\mu\textrm{N}$의 힘으로 시편에 압입을 시켜 재료의 경도나 탄성계수와 같은 기계적 특성을 평가하는 압입경도 시험법이다. 압입 변위를 나노미터범위로 조절할 수 있어 기존에 접근할 수 없었던 박막의 기계적 특성을 평가하는데 응용이 넓어지고 있다. 본 연구에서는 나노인덴테이션에서 제공되는 하중-변위곡선과 유한요소해석의 결과를 비교하여 유한요소해석의 신뢰성을 검증하고, 유한요소해석에서 여러 가지 재료의 특성에 따른 파일업과 싱크인 현상을 규명 하고자 한다.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.93-103
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• 2005

Both static pile load test with load transfer measuring system and the pile dynamic load test are performed to estimate the skin friction and behavior characteristics of a large drilled shaft. And the numerical modeling of large drilled shaft is performed by applying the FDM program. Since the magnitude of friction resistance depends on the relative displacement between soil and shaft, load and displacement at the arbitrary depth along the large drilled shaft are estimated to analyze the correlation. According to the measuring results of load transfer, unit skin friction along the large drilled shaft was fully mobilized at gravel layer in the middle of shaft and the frictional resistance transmitted to bedrock was relatively small. Also, even for the same drilled shaft, the results of PDA and static load test are different with each other and the difference is discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.17-28
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• 2012

In this study, we suggest a method for material property evaluation by dual-triangular pyramidal indenters using the reverse analysis. First, we demonstrated that load-displacement curves of conical and triangular pyramidal indenters are different for the same material. For this reason, an independent research on the triangular pyramidal indenter is needed. From FE indentation analyses on various materials, we then investigated the relationships among material properties, indentation parameters and load-displacement curves. From this, we established property evaluation formula using dual-triangular pyramidal indenters having two different half-included-angles. The approach provides the values of elastic modulus, yield strength and strain-hardening exponent within an average error of 3% for various materials.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.157-164
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• 2010

This research was conducted to analyze the behavior of Single-PTAS (Single Post-Tensioned Approach Slab) under tensioning and environmental loads by performing field tests when the demonstration Single-PTAS was being constructed. The temperature measurement sensors were installed at different depths, and the displacements in the approach slab under environmental loads and tensioning were measured using displacement transducers. As an experimental result, an abrupt change in the longitudinal displacement due to tensioning was not observed. The daily temperature change in the approach slab was negligible where the depth is over about 35cm. The temperature gradient in the approach slab adjacent to bridge was smaller than that adjacent to pavement. The patterns and magnitudes of vertical displacements were directly related to the temperature gradient at the measuring location. The behavior of Single-PTAS was very similar to that of concrete pavement. Therefore, a new design methodology for approach slabs is needed to include the pavement concept and to overcome drawback of current design procedures based on the simple beam concept.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.181-189
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• 2009

This study is to evaluate an effect of supports with respect to these supports after comparing the characteristic of support between rock bolt of a widely used type and spiral bolt of a new type. For these purposes, we performed pull-out test in laboratory about rock and spiral bolts in the case of cement-mortar grout curing periods, 7 and 28 days, then calculated pull-out load, displacement, external pressure, inner pressure and shear stress using data obtained from the results of pull-out test, respectively. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. We found that because adhesive force between supports and cement-mortar grout is increasing with compressive strength of grout according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.3
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• pp.123-129
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• 2002

본 논문에서는 다목적실용위성 1호 개발 과정 중에 수행했던 연성 하중 해석에 대하여 소개하였다. 먼저 일반적인 연성 하중 해석 과정과 다목적실용위성 개발시 수행한 실제의 과정을 비교하였다. 그리고, 다목적실용위성 1호의 유한요소모델과 본 해석에 관련된 각 기관들의 역할을 설명하였다. 준비행모델의 진동 시험 결과를 이용한 유한요소모델의 조정에 대하여 설명하고, 또한, 해석에 입력으로 사용되는 외력함수에 해당하는 하중들에 대하여 설명하였다. 대표적인 해석 결과들을 제시하여 위성이 발사하중에 대하여 안전하다는 것이 예측되었음을 보여 주었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.519-525
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• 2009

In this study a cohesive zone model was used to simulate the delamination phenomena which occurs by a successive crack initiation and propagation in composite laminates. The cohesive zone model was incorporated to the classical finite element method via cohesive element formulation and then implemented into the user-subroutine UEL of a commercial finite element program Abaqus. To validate the formulation and implementation of the cohesive element the finite element results were compared with the experimental data of double cantilever beam and end notched flexure tests. The numerical results well agree with the experimental load-displacement curves. Also the effect of the elastic stiffness and the size of the cohesive element on the global load-displacement curves were studied numerically. To minimize the mesh-dependency of the crack propagation path and eliminate the zig-zag patterns in the load-displacement curve, cohesive elements should be refined at the crack-tip.

• Journal of the Korean Geotechnical Society
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• v.33 no.5
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• pp.37-44
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• 2017

In this study, three dimensional numerical analyses were carried out to predict axial (pullout and compressive) and lateral behavior of rock-socketed steel pipe pile varying diameter, wall thickness, and length. As a result of the pile pullout analyses, it was confirmed that the pullout displacement was inversely proportional to the pile diameter for given pile length, thickness, pullout load. Load-settlement relationship of the compressive pile analyses revealed that the effect of pile thickness on pile resistance was more significant than that of pile diameter. In addition, laterally loaded pile analyses showed that pile lateral resistance is influenced above all else by pile diameter. This study showed that it is necessary to conduct numerical analyses to identify the effects of pile diameter, wall thickness, and pile length on the steel pipe pile behavior as a preliminary pile design under specified loading conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1947-1955
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• 2013

The purpose of this paper is to present an photoelasticity technique for measuring the displacement and stress distribution in particle assembly subjected to shallow foundation loading. Photoelastic measurement technique was employed to visualize the force transmission of a particle assembly. A model assembly bounded by a steel frame was built by stacking bi-dimensional circular particles made of polycarbonate elastomer. Each particle was coated by a thin photoelastic sheet so that the force transmission represented by bright light stripes can be visualized. In a contacted particle, both magnitude and orientation of principal stress difference can also be measured via the photoelasticity technique. The different distributions of the contact stresses at the initial loading and near the failure were quantitatively compared. The photoelastic patterns and displacement fields observed in the pre-failure state disappears immediately after the buckling of confined force chains.

• Tunnel and Underground Space
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• v.16 no.2 s.61
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• pp.166-178
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• 2006

Recently, the frequency of occurring dynamic events such as earthquakes, explosives blasting and other types of vibration has been increasing. Besides, the chances of exposure for rock discontinuities to free faces get higher as the scale of rock mass structures become larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, artificially fractured rock joint specimens were prepared in order to examine the dynamic frictional behavior of rough rock joint. Roughness of each specimen was characterized by measuring surface topography using a laser profilometer and a series of shaking table tests was carried out. For mated joints, the static friction angle back-calculated ken the yield acceleration was $2.7^{\circ}$ lower than the tilt angle on average. The averaged dynamic friction angle for unmated joints was $1.8^{\circ}$ lower than the tilt angle. Displacement patterns of sliding block were classified into 4 types and proved to be related to the first order asperity of rock joint. The tilt angle and the static friction angle for mated joints seem to be correlated to micro average inclination angle which represents the second order asperity. The tilt angle and the dynamic friction angle for unmated Joints, however, have no correlation with roughness parameters. Friction angles obtained by shaking table test were lower than those by direct shear test.