• Title/Summary/Keyword: displacement and strain measurement

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A Study on behavior of Slope Failure Using Field Excavation Experiment (현장 굴착 실험을 통한 사면붕괴 거동 연구)

  • Park, Sung-Yong;Jung, Hee-Don;Kim, Young-Ju;Kim, Yong-Seong
    • Journal of The Korean Society of Agricultural Engineers
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    • v.59 no.5
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    • pp.101-108
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    • 2017
  • Recently, the occurrence of landslides has been increasing over the years due to the extreme weather event. Developments of landslides monitoring technology that reduce damage caused by landslide are urgently needed. Therefore, in this study, a strain ratio sensor was developed to predict the ground behavior during the slope failure, and the change in surface ground displacement was observed as slope failed on the field model experiment. As a result, in the slope failure, the ground displacement process increases the risk of collapse as the inverse displacement approaches zero. It is closely related to the prediction of precursor. In all cases, increase in displacement and reverse speed of inverse displacement with time was observed during the slope failure, and it is very important event for monitoring collapse phenomenon of risky slopes. In the future, it can be used as disaster prevention technology to contribute in reduction of landslide damage and activation of measurement industry.

Comparison of dynamic and static methods in the measurement of the initial stiffness of soil (동적 및 정적 실험 방법으로 평가한 지반의 초기 강성 비교)

  • Choo, Jin-Hyun;Jung, Young-Hoon;Chung, Choong-Ki
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.03a
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    • pp.940-951
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    • 2009
  • A comparative study on dynamic and static measurement of initial stiffness was conducted. Because soil stiffness decreases even at very small strains, the initial stiffness has been measured by dynamic tests using shear wave velocity measurement. On the other hand, due to the advance of local strain measurement, the triaxial testing device is capable of measuring the static initial stiffness. It has been known that initial stiffness measured by static triaxial tests is generally lower than that measured by dynamic tests possibly due to the limitation of static measurement of displacement at very small strains. This study presents experimental results indicating that the elastic shear moduli could be the same both in dynamic and static measurements owing to the soil anisotropy induced by anisotropic stresses.

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Study on the Fiber Bragg Grating Sensors for Smart Structures and Their Applications (스마트 구조물용 광섬유 격자센서 및 그 응용)

  • Kim Ki-Soo;Song Young-Chul;Pang Gi-Sung
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2004.04a
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    • pp.115-118
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    • 2004
  • In this paper, a Fiber Bragg Grating (FBG) sensor system for smart structures is described. FBGs are well-suited for long term and extremely severe experiments, where traditional strain gauges fail. In the system, a reflect wave-length measurement method which employs a tunable light source to find out the center wave-length of FBG sensor is used. We applied the FBG system to composite repairing structures and beam column joint of building structure. We also applied the system to nuclear energy power plant for structural integrity test to measure the displacement of the structure under designed pressure and to check the elasticity of the structure by measuring the residual strain. The system works very well and it is expected that it can be used for a real-time strain, temperature and vibration detectors as parts of smart structures.

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The Rate Dependent Deformation Behavior of AISI Type 304 Stainless Steel at Room Temperature (304 스테인리스강의 점소성 특성에 관한 연구)

  • Ho, Kwang-Soo
    • Transactions of Materials Processing
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    • v.16 no.2 s.92
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    • pp.101-106
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    • 2007
  • Uniaxial displacement controlled tests were performed on annealed Type 304 stainless steel at room temperature. A servo-controlled testing machine and strain measurement on the gage length were employed to measure the response to a given input. The test results exhibit that the flow stress increases nonlinearly with the strain rate and the relaxed stress at the end of the relaxation periods depends strongly on the strain rate preceding the relaxation test. The rate-dependent inelastic deformation behavior is simulated using a new unified viscoplasticity model that has the rate-dependent format of nonlinear kinematic hardening rule, which plays a key role in modeling the rate dependence of relaxation behavior. The model does not employ yield or loading/unloading criteria and consists of a flow law and the evolution laws of two tensor and one scalar-valued state variables.

System Integration Test System Integration Test of Containment Structure of Nuclear Power Plant Using Fiber Optic Sensor (광섬유센서를 이용한 원자력 발전소 격납구조물의)

  • 김기수
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2003.10a
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    • pp.519-526
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    • 2003
  • In this paper, a Fiber Bragg Grating (FRG) sensor system is described and FBGs are well-suited for long term and extremely severe experiments, where traditional strain gauges fail. In the system, a reflect wave-length measurement method which employs a tunable light source to find out the center wave-length of FBG sensor is used. We apply the FBG system to nuclear energy Power Plant for structural integrity test to measure the displacement of the structure under designed pressure and to check the elasticity of the structure by measuring the residual strain. The system works very well and it is expected that it can be used for a real-time strain. temperature and vibration detector of smart structure.

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Fabrication of a Multiplexing Sensor Probe for Measuring the Blade Deflection of a Wind Power Generator (풍력발전기 블레이드 처짐 측정을 위한 다중화 센서 탐촉자 설계 제작)

  • Kim, Ji-Dea;Lee, Dong-Ju
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.23 no.2
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    • pp.178-185
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    • 2014
  • This paper describes a fabrication multiplexing sensor probe that employs a fiber Bragg grating(FBG) based on multiple measurements to determine the blade deflection of a wind power generator the reliability analysis of this probe is also presented. To diminish the temperature sensitivity of the FBG sensor, we form multiple CFRPs onto the upper and lower layers of the FBG and package it with an epoxy resin. As a result, the depth of the CFRP is 1mm, and the temperature sensitivity is $2.39pm/^{\circ}C$. We construct a sensor network utilizing the fabricated sensor with a blade beam model. As the number of pendulums is increased on the fore-end of the beam, the strain value is measured. The strain variation is calculated from the measurement of the load on the blade beam model by monitoring the strain of the FBG sensor. When the linear equation is applied, the strain error is 0.4% and when the finite difference method is used, the tip deflection error is 3.3%. The displacement error derived from the strain value of the FBG sensor is 4.39%. The calculated result between the measured value of the dead-end of the beam and the strain is less than 2.46% tip distortion error. Therefore, our proposed multiplexing sensor probe is a low-cost and high-reliability solution for a commercial wind power generator.

Evaluation of Fatigue Crack Growth Rate on the Surface of Steel Members Using COD(Crack Opening Displacement) Measurement (COD(Crack Opening Displacement) 측정에 의한 강재표면의 피로균열진전속도 평가)

  • Kim, Kwang Jin;Kim, In Tae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.2
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    • pp.179-188
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    • 2011
  • Steel structures have been allowed to have fatigue damage tolerance in fact. If it would be assessed whether fatigue crack is growing or not and How fast fatigue crack is propagating, we should make a rational decision on methods and a period of reinforcement in the maintenance. In this study, fatigue crack growth tests on two kinds of through-thickness cracked steel plates and a out-of-plane gusset welded joint were conducted to evaluate fatigue crack growth rate using the COD(Crack Opening Displacement), and COD measurement using strain gauges was examined to offer a practical method. As a result, we proposed a reasonable assessing method for fatigue crack growth rate using the COD and it was experimentally proved practical to estimate the COD through measuring strains.

Technique for the Measurement of Crack Widths at Notched / Unnotched Regions and Local Strains (콘크리트의 노치 및 비노치 구역에서의 균열폭 및 국부 변형률 정밀 측정기법)

  • Choi, Sok-Hwan;Lim, Bub-Mook;Oh, Chang-Kook;Joh, Chang-Bin
    • Journal of the Korea Concrete Institute
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    • v.24 no.2
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    • pp.205-214
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    • 2012
  • Crack widths play an important role in the serviceability limit state. When crack widths are controlled sufficiently, the reinforcement corrosion can be reduced using only existing concrete cover thickness due to low permeability in the region of finely distributed hair-cracks. Thus, the knowledge about the tensile crack opening is essential in designing more durable concrete structures. Therefore, numerous researches related to the topic have been performed. Nevertheless accurate measurement of a crack width is not a simple task due to several reasons such as unknown potential crack formation location and crack opening damaging strain gages. In order to overcome these difficulties and measure precise crack widths, a displacement measurement system was developed using digital image correlation. Accuracy calibration tests gave an average measurement error of 0.069 pixels and a standard deviation of 0.050 pixels. Direct tensile test was performed using ultra high performance concrete specimens. Crack widths at both notched and unnotched locations were measured and compared with clip-in gages at various loading steps to obtain crack opening profile. Tensile deformation characteristics of concrete were well visualized using displacement vectors and full-field displacement contour maps. The proposed technique made it possible to measure crack widths at arbitrary locations, which is difficult with conventional gages such as clip-in gages or displacement transducers.

Applicability estimation of ESPI on the vibration mode analysis of rectangular plate (직사각형 평판의 진동모드 해석에 관한 ESPI의 적용성 평가)

  • 김경석;정현철;박경주;양승필
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.61-67
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    • 1997
  • The electronic speckle pattern interferometer (ESPI) has been applied to many technical problems such as deformation and displacement measurement, strain visualization and surface roughness monitoring. In this study, we used an ESPI system based on the dual beam speckle interferometer method in order to measure in-plane displacement and vibration mode using the ESIP technique. This research was carried out for the purpose of applying the vibration analysis method employing Electro-Optic holographic interference technique to the vibration analysis of uniform rectangular cantilevers plate(SS400,STS304) with cantilevers span to breadth ratio of 150 by 75. And thickness of 1mm and 0.8mm respectively. We improved the ESPI technique in order to obtain the distribution of displacement component resolved in one direction through a CCD camera combined with an image processing system. To certify and to assess the accuracy in measuring by this ESPI, the results obtained with the speckle method and vibration mode analysis are to be compared with those results by Warbuton's Theoretical expression and vibration made in FEM analysis.

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Advances in measuring linear viscoelastic properties using novel deformation geometries and Fourier transform techniques

  • See, Howard
    • Korea-Australia Rheology Journal
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    • v.13 no.2
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    • pp.67-81
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    • 2001
  • The development of new techniques for the dynamic measurement of linear viscoelastic properties is an active area of rheometry, and this paper surveys some novel deformation geometries which have been recently reported e.g. oscillating probe-type devices which are imbedded in or placed on the surface of the sample. Small amplitude band-limited pseudorandom noise is used for the displacement signal, with Fourier analysis of the complex waveform of the resistance force yielding the frequency dependent viscoelastic material functions (e.g. storage and loss moduli G", G"). Theoretical calculations of the fundamental equations relating force to displacement and instrument geometry, were carried out with the aid of the correspondence principle of linear viscoelasticity. The rapidity of the tests and flexibility in terms of sample preparation and stiffness mean that this basic technique should find many applications in rheometry. Three examples of oscillatory tests are presented in detail squeeze flow, imbedded needle and concentric sliding cylinder geometries.eometries.

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