• Title/Summary/Keyword: 하중봉

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Elastic and plastic behaviors of materials during the nanoindentation testing (나노인덴테이션 시험시 재료의 탄성.소성 변형거동)

  • 김지수;윤존도;김봉섭;고철호;이홍림;양현윤;조상봉
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2003.03a
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    • pp.244-244
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    • 2003
  • 나노인덴테이션은 시편에 압자를 침투시켜 재료의 기계적 특성을 파악할 수 있는 경도시험법이다. 압입범위를 나노미터범위로 조절할 수 있어 기존에 접근할 수 없었던 극 미소부분에로 응용이 넓어지고 있다. 경도시험시 재료의 탄성 및 소성 작용에 의해 재료는 변형되고, 표면변화 관찰을 통해 표면아래 부분에서 이루어지고 있는 거동을 예측할 수 있다. 이러한 관점에서 나노인덴테이션 시험시에도 발생하는 파일업과 싱크인 현상에서 재료가 나노미터 범위에서 어떠한 양상으로 변형을 하는지를 고찰하는 것은 의미가 있을 것이다. 본 연구에서 파일업과 싱크인의 양상을 파악하고 그 양을 정량화하기 위하여 가공경화양에 따른 표면변화와 압입하중 변화에 따른 표면변화를 관찰하였다. 어닐링한 봉상 알루미늄을 압축변형을 0%, 5%, 20%, 40%, 50% 로 변형시켜 가공경화를 일으켰고, 표면은 전해연마하여 나노압입시험이 가능하도록 하였다. 각각의 시편을 나노인덴테이션 압입하중을 변화시켜 재료에서 하중 변화에 따라 나타나는 표면변화를 관찰하였고, 위의 각 조건에서 파일업양을 정량화 하였다. 연구결과에 대해 ANSYS 유한요소분석 프로그램을 사용하여 재료의 변형양상을 시뮬레이션 하였고, 실제 실험데이터와 비교 분석하였다.

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Deformation Behaviors of Materials under Nanoindentation and Their Simulation by Three Dimensional FEM Analysis (재료의 나노압입변형과 그에 대한 3차원 FEM분석)

  • 김지수;양현윤;김봉섭;윤존도;조상봉
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2003.11a
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    • pp.38-38
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    • 2003
  • 최근 나노기술의 발달과 더불어 나노재료에 대한 특성평가 요구가 높아지고 있고, 따라서 나노스케일로 재료의 기계적 거동을 분석할 수 있는 나노인덴테이션 기법이 심도있게 연구되고 있다. 본 연구에서는 나노인덴테이션을 이용하여 여러 가지 재료의 탄성 소성 변형 거동을 관찰 조사하고 이를 다시 유한요소법(FEM)으로 모사하여 해석하였다. 나노인덴테이션으로 재료 표면에 압입하여 탄소성 변형을 일으켰으며 이때의 가하중과 변형깊이를 측정하여 하중-변형 곡선을 얻었다. 매우 작은 접촉응력 조건하에서는 탄성변형의 비율이 매우 높았는데 하중-변형 곡선으로부터 재료의 나노 경도와 탄성 계수값을 얻을 수 있었다. 실험적으로 얻은 하중-변형 곡선을 3 차원의 유한요소법(FEM)을 이용하여 모사하였는데 상호간에 매우 근접한 결과를 얻을 수 있었다. 이 때 압자의 모양, 압입 깊이, 재료의 종류, 둥을 변수로 하여 여러 가지 조건하에서 압입실험을 하였으며 그 결과를 유한요소법으로 모사하였다.

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The Earth Pressure on the Effect of Surcharge Load at the Narrowly Backfilled Soil (좁은 공간 되메움 지반에서의 상재하 영향에 의한 토압)

  • 문창열;이종규
    • Geotechnical Engineering
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    • v.13 no.6
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    • pp.165-180
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    • 1997
  • The structure such as underground external walls of buildings, conduit and box culvert supports the surcharge loads (point, strip and line loads) . The vertical and horizontal stresses in a soil mass depend on the backfill width and wall friction, etc. The investigations described in this paper is designed to identify the magnitude and the distributions of the lateral and vertical pressure which is occurred by the narrowly backfilled soil in an open cut by the surcharge loads. For these purposes, model tests were performed for various width of backfill in a model test box by considering the wall friction using carbon rods. The results of test were compared with the theories of Weissenbach and VS Army Code and also with the results of the numerical analysis using finite difference method which introduces Mohr-Coulomb failure hypothesis.

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A Study on the Verification Test for a Deformable Rod Sensor (변형봉 센서 검증실험에 관한 연구)

  • 김상일;최용규;이민희
    • Journal of the Korean Geotechnical Society
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    • v.19 no.5
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    • pp.35-47
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    • 2003
  • In the conventional axial load transfer analysis for composite piles (i.e., steel pipe pile filled with concrete), it was assumed that the concrete's strain is same as the measured steel's strain and the elastic modulus of the steel and the concrete calculated by formular as prescribed by specification is used in calculation of pile axial load. But, the pile axial load calculated by conventional method had some difference with the actual pile load. So, the behavior of a composite pile could not be analyzed exactly. Thus, the necessity to measure the strain for each pile components was proposed. In this study, the verification test for DRS (Deformable Rod Sensor) developed to measure the strain of each pile component (i.e., the steel and the concrete) was performed. In the calculation of pile axial load using the DRS, elastic modulus of concrete could be determined by the uniaxial compression test for the concrete cylinder samples made in the test site and an average tangential modulus in the stress range of (0.2∼0.6)f$_ck$ was taken.

Development of an Improved Point Load Apparatus (개량형 점하중강도시험기의 개발)

  • Kim, Yong-Phil;Um, Jeong-Gi
    • Tunnel and Underground Space
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    • v.19 no.6
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    • pp.473-478
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    • 2009
  • The accuracy of point load apparatus is depend on point to point coaxial fitting. Also, the estimation of applied point load using the pressure gauge frequently lead to erroneous results. An improved point load apparatus has been developed in this study by mounting linear bearing on polished support rod, and eccentric error of point to point axis has been sustained less than 0.1 mm even under series of extreme work load conditions. Two digital displacement gauges are attached to measure the distance from point to point with sample specimen. A load cell mounted at the end of upper conical platen measure the applied net load on sample instead of preassure gauge. Total of 107 point load tests has been achieved to assure the quality and performance of developed apparatus. This exercise turned out to be successful.

A study on wear mechanism of tube fretting affected by support shapes (지지부 형상에 따른 튜브 프레팅 마멸기구의 연구)

  • Lee, Yeong-Ho;Kim, Hyeong-Gyu;Ha, Jae-Uk
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2002.05a
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    • pp.73-79
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    • 2002
  • Fretting wear test in room temperature air was performed to evaluate the wear mechanism of fuel rod using a fretting wear tester, which has been developed for experimental study. The main focus was to compare the wear behaviors of fuel rod against support springs at different contact geometries (i.e. concave and convex) and slip directions (axial and transverse). The wear on the tube was examined by the surface roughness tester, which measures the volume. The result indicated that with change of contact geometry from 5N of normal load to 0.1mm gap, wear volume of tube Increased in the condition of concave spring, but slowly decreased in convex spring. From the results of SEM observation, wear mechanism of each test condition was also depend on the above contact parameters. The wear mechanism of each test condition in room temperature air is discussed.

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Mechanical Characterization of the Pedicle Screw System for Thoracolumbar Spine (흉요추용 척추경 나사못시스템의 기계적 특성)

  • 이효재;최화순;안면환;송정일
    • Journal of Biomedical Engineering Research
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    • v.23 no.1
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    • pp.17-26
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    • 2002
  • The purpose of this study was to investigate the important Parameters of the Pedicle screw by estimating the mechanical characteristics of screws under static and dynamic loads. Methodology for estimating Parameters under static load was proposed. It was also shown that the fatigue life of the one-level system could be increased by changing the shape of screws. Load parameters of the single pedicle screw were friction force. bending moment. and holding force. The test results of the one-level system could be inferred from teat results of the sin91e screw under bending force Fatigue life of the one-level system with flexible rod was longer than that of the upper Part test without rod . Considering the drop of flexibility of the rod due to muscles and ligament, fatigue life of the one-level system could be estimated b? that of the single screw.

Analysis of Apparatus Variables for Deformation Strength Test of Asphalt Concrete Based on Correlation with Rutting and Prediction Model for Rutting (소성변형과의 상관성 및 추정모델을 통한 변형강도 시험장치 변수 분석)

  • Kim, Kwang-Woo;Lee, Moon-Sup;Kim, Sung-Tae;Lee, Soon-Jae
    • International Journal of Highway Engineering
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    • v.4 no.4 s.14
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    • pp.41-52
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    • 2002
  • This study dealt with analysis of size effect of testing apparatus for Kim test which measures rut resistance characteristics of asphalt mixture under static loading. Two columns in different diameter with each column having different radios of round cut (Curvature) at the bottom were used for testing asphalt mixture. Deformation load ($P_{max}$) and deformation strength ($K_D$) were found to have relatively high correlation with rut depth and dynamic stability of asphalt concrete. Diameter of specimen was not a significant factor in this test. From the statistical correlation analysis with rutting properties, the radius of curvature and diameter of loading column were found to be important factor affecting the results of the test. Among the radios (r) of curvatures, r=0.5cm and 1.0cm showed much higher correlation than the column without curvature, and r=1.0cm being better between the two. The column with diameter of 4cm showed better correlation than diameter of 3cm. Therefore, the column of 4cm diameter with r=1.0cm was found to be the best among various apparatus sizes. Prediction models for rut depth and dynamic stability were developed for each aggregate mixture based on Kim test variables using SAS STEPWISE procedure. Therefore, if this test method is validated through further study, Kim test can be used for selecting asphalt mixture with the highest resistance against permanent deformation.

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Finite Element Analysis in Finite Length Bar under Constant Amplitude Loading (일정진폭하중을 받는 유한 길이 봉의 유한요소해석)

  • Hwang, Eun-Ha
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.23 no.5
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    • pp.525-533
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    • 2010
  • Direct time integration method such as Newmark method is numerically performed under the assumption that continuous load function such as constant amplitude load can be treated as a discontinuous load fuction. It is due that the load can be treated as a constant value at the given time period regardless of variation of load at the time increment interval. It means the numerical results should be accompanied by the error due to approximation of load fuction. In contrast, the load function is calculated by convolution integral for the given time interval at finite element equation based on Gurtin's variation equation. Therefore. precise numerical results can be obtained by Gurtin's method because of convolution integral for the continuous load fuction curve even at the variation of load function in the given time interval. In this study, we prove that Gurtin's method can be more suitable than Newmark method in the problem of constant amplitude loading, using the numerical results for the free end of the one-dimensional rod. This study also shows that Gurtin's method is more effective in constant amplitude loading than in constant loading. The accuracy and the validity are verified by comparison between the results of in-house FORTRAN code and ADINA, a commercial software supporting Newmark method.

Nonlinear Impact Analysis of CEDM Seismic Cap Plates for Seismic Loading (지진하중에 의한 제어봉구동장치 내진지지판의 비선형 충격해석)

  • Kang, Tae-Kyo;Kim, Tae-Hyung;Lee, Dae-Hee;Choi, Taek-Sang
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.435-440
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    • 2004
  • The nonlinear impacts between the Control Element Drive Mechanisms (CEDMs) seismic cap plates installed on the CEDM top of a pressurized water reactor are studied with the dynamically reduced models of the CEDM and Integrated Head Assembly (IHA). It is important to develope nonlinear models considering the gap effects between the plates. In order to simulate impacts, reduced models for the primary structures, such as CEDM and IHA, are developed through simplifying detailed models, and the nonlinear structural analysis is performed under seismic loading conditions. The responses are examined in various gap sizes depending on the reactor operating conditions.

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