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Continuous deformation measurement for track based on distributed optical fiber sensor

  • He, Jianping;Li, Peigang;Zhang, Shihai
    • Structural Monitoring and Maintenance
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    • v.7 no.1
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    • pp.1-12
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    • 2020
  • Railway tracks are the direct supporting structures of the trains, which are vulnerable to produce large deformation under the temperature stress or subgrade settlement. The health status of track is critical, and the track should be routinely monitored to improve safety, lower the risk of excess deformation and provide reliable maintenance strategy. In this paper, the distributed optical fiber sensor was proposed to monitor the continuous deformation of the track. In order to validate the feasibility of the monitoring method, two deformation monitoring tests on one steel rail model in laboratory and on one real railway tack in outdoor were conducted respectively. In the model test, the working conditions of simply supported beam and continuous beam in the rail model under several concentrated loads were set to simulate different stress conditions of the real rail, respectively. In order to evaluate the monitoring accuracy, one distributed optical fiber sensor and one fiber Bragg grating (FBG) sensor were installed on the lower surface of the rail model, the strain measured by FBG sensor and the strain calculated from FEA were taken as measurement references. The model test results show that the strain measured by distributed optical fiber sensor has a good agreement with those measured by FBG sensor and FEA. In the outdoor test, the real track suffered from displacement and temperature loads. The distributed optical fiber sensor installed on the rail can monitor the corresponding strain and temperature with a good accuracy.

Efficacy of the Velocity Variance Model to Estimate the Thickness Irregularity in a Fiber Bundle Flow (집속 유동에서 속도분산모형과 집속체 불균제 예측성)

  • Lim, Jung-H.;Kim, Jong-S.;Huh, You
    • Textile Science and Engineering
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    • v.48 no.6
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    • pp.371-379
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    • 2011
  • This study reports on the output linear density that was attained by simulation for various levels of draft roller gauge and draft ratio, based on the dynamic model with approximated sinusoidal velocity variance model to specific fiber length distributions to test the model feasibility, while a random variation for the input bundle linear density was provided. Results from model simulation showed that a process resonance could take place, when the draft roller gauge or draft ratio reached the critical values, because there were fundamental frequencies which spread in the irregularity of the bundle linear density, giving rise to some resonance. Thus, the irregularity of the output linear density began increasing steeply. From the view point of the output linear density as a whole, the irregularity decreased, as the draft roller gauge increased. A process resonance occurred in the range of draft roller gauge between 1.25 and 1.5 multitudes of the (maximal) fiber length. Length distribution led to a lower fundamental frequency (longer fundamental wavelength) than the uniform fiber length. High draft ratio yielded high irregularity in the output bundle. Especially, the process resonance occurred between the draft ratio 20 and 30. In the draft ratio range higher than 30, the output included wide-ranged regularly oscillatory components of irregularity that corresponded to the integer-multiple of the fundamental frequency, which shifted to a higher value, when the fiber length was distributed. In addition, the approximated sinusoidal velocity variance model turned out to be adequate to estimate the irregularity of the bundle linear density with both the uniform and the quadratic fiber length distribution.

Nonlinear analysis and tests of steel-fiber concrete beams in torsion

  • Karayannis, Chris G.
    • Structural Engineering and Mechanics
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    • v.9 no.4
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    • pp.323-338
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    • 2000
  • An analytical approach for the prediction of the behaviour of steel-fiber reinforced concrete beams subjected to torsion is described. The analysis method employs a special stress-strain model with a non-linear post cracking branch for the material behaviour in tension. Predictions of this model for the behaviour of steel-fiber concrete in direct tension are also presented and compared with results from tests conducted for this reason. Further in this work, the validation of the proposed torsional analysis by providing comparisons between experimental curves and analytical predictions, is attempted. For this purpose a series of 10 steel-fiber concrete beams with various cross-sections and steel-fiber volume fractions tested in pure torsion, are reported here. Furthermore, experimental information compiled from works around the world are also used in an attempt to establish the validity of the described approach based on test results of a broad range of studies. From these comparisons it is demonstrated that the proposed analysis describes well the behaviour of steel-fiber concrete in pure torsion even in the case of elements with non-rectangular cross-sections.

Statistical methods of investigation on the compressive strength of high-performance steel fiber reinforced concrete

  • Ramadoss, P.;Nagamani, K.
    • Computers and Concrete
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    • v.9 no.2
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    • pp.153-169
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    • 2012
  • The contribution of steel fibers on the 28-day compressive strength of high-performance steel fiber reinforced concrete was investigated, is presented. An extensive experimentation was carried out over water-cementitious materials (w/cm) ratios ranging from 0.25 to 0.40, with silica fume-cementitious materials ratios from 0.05 to 0.15, and fiber volume fractions ($V_f$= 0.0, 0.5, 1.0 and 1.5%) with the aspect ratios of 80 and 53. Based on the test results of 44 concrete mixes, mathematical model was developed using statistical methods to quantify the effect of fiber content on compressive strength of HPSFRC in terms of fiber reinforcing index. The expression, being developed with strength ratios and not with absolute values of strengths, is independent of specimen parameters and is applicable to wide range of w/cm ratios, and used in the mix design of steel fiber reinforced concrete. The estimated strengths are within ${\pm}3.2%$ of the actual values. The model was tested for the strength results of 14 mixes having fiber aspect ratio of 53. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values of different researchers. Equation is also proposed for the size effect of the concrete specimens.

Nonlinear Elastic Analysis of Thick Composites with Fiber Waviness Using a FEA Model (FEA 모델을 이용한 굴곡진 보강섬유를 가진 두꺼운 복합재료의 비선셩 거동에 관한 연구)

  • 이승우;전흥재
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.43-47
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    • 1999
  • A FEA model is proposed to study the effects of fiber waviness on tensile/comprssive nonlinear behaviors of thick unidirectional composites. In the analyses both material and geometical nonlinarities are considered. The predicted results from the FEA model are compared with those obtained from the previous analytical model (thin carpet model) Tensile/compressive tests are also conducted on the specimens with various controlled fiber waviness to obtain the nonlinear behaviors of composites experimentally. The predictions from the FEA model show better agreements with the experiments than those from the analytical model.

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A study on the development of photoelastic model material with shape memory effect (형상기억효과를 가진 투과형 광탄성 실험용 모델재료 개발에 관한 연구)

  • Lee, Hyo-Jae;Hwang, Jae-Seok;Shimamoto, Akira
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.3
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    • pp.624-634
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    • 1998
  • The photoelastic model material with shape memory effect and the molding processes for the material are developed in this research. The matrix and fiber of the photoelastic model material developed in this research are epoxy resin (Araldite to hardner 10 to 3 (weight ratio)) and wire of $Ti_50-Ni_50$ shape memory alloy, respectively. It is called Ti50-Ni50 Shape Memory Alloy Fiber Epoxy Composite $(Ti_50-Ni_50SMA-FEC).$ Ti50-Ni50 SMA-FEC is satisfied with the requirements of the photoelastic model material and can be used as a photoelastic model material. The maximum recovering strain of $Ti_50-Ni_50$SMA-FEC is occurred at $80^{\circ}C$ in any prestrain of $Ti_50-Ni_50$ shape memory alloy fiber and in any fiber volume ratio. Recovering strain(force) is increased with the increment of the prestrain and the fiber volume ratio. The best prestrain of $Ti_50-Ni_50$SMA-FEC is 5% for the recovering force among 1%, 3%, 5%.

Effect of the Variation of Fiber Openness on the Draft Irregularity (Fiber Openness의 변동이 Draft 불균제에 미치는 영향)

  • Heo, Yu;Kim, Jong-Sung;Kwak, Dowoong
    • Proceedings of the Korean Fiber Society Conference
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    • pp.157-160
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    • 2003
  • 드래프트 공정을 거친 슬라이버의 선밀도 불균제는 제품의 품질과 공정의 효율 면에서 많은 문제를 일으킨다. 이러한 불균제의 특성을 해석하고 균제성을 제고하기 위해서는 실제 불균제가 발생하는 드래프트 존 내에서 섬유집속체의 동적거동을 정확하게 묘사해 줄 이론적 모델 연구가 필요하다. 본 연구에서는 이미 제시한 드래프트 존 내에서의 섬유의 동적거동을 묘사하는 fundamental equation을 바탕으로 force-deformation의 관계를 나타내는 constitutive model의 주요 model parameter 변동이 출력 슬라이버의 두께 flucturation에 미치는 영향으르 찾아보기 위하여 model simulation을 하고, fiber openness와 직접적인 관련이 있는 model parameter u의 변동범위를 실험을 통해 살펴보았다. (중략)

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Viscoelastic behavior on composite beam using nonlinear creep model

  • Jung, Sung-Yeop;Kim, Nam-Il;Shin, Dong Ku
    • Steel and Composite Structures
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    • v.7 no.5
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    • pp.355-376
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    • 2007
  • The purpose of this study is to predict and investigate the time-dependent creep behavior of composite materials. For this, firstly the evaluation method for the modulus of elasticity of whole fiber and matrix is presented from the limited information on fiber volume fraction using the singular value decomposition method. Then, the effects of fiber volume fraction on modulus of elasticity of GFRP are verified. Also, as a creep model, the nonlinear curve fitting method based on the Marquardt algorithm is proposed. Using the existing Findley's power creep model and the proposed creep model, the effect of fiber volume fraction on the nonlinear creep behavior of composite materials is verified. Then, for the time-dependent analysis of a composite material subjected to uniaxial tension and simple shear loadings, a user-provided subroutine UMAT is developed to run within ABAQUS. Finally, the creep behavior of center loaded beam structure is investigated using the Hermitian beam elements with shear deformation effect and with time-dependent elastic and shear moduli.

A Study on the Composite Strengthening Effect in Metal Matrix Composites (단섬유 금속복합체에서의 복합강화효과에 관한연구)

  • 김홍건
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • pp.61-66
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    • 1996
  • An overall feature to simulate composite behavior and to predict closed solution has been performed for the application to the stress analysis in a discontinuous composite solid. To obtain the internal field quantities of composite, the micromechanics analysis and finite element analysis (FEA) were implemented. For the numerical illustration, an aligned axisymmetric single fiber model has been employed to assess field quantities. Further, a micromechanics model to describe the elastic behavior of fiber or whisker reinforced metal matrix composites has been developed and the stress concentrations between reinforcements were investigated using the modified shear lag model with the comparions between reinforcements were investigated using the modified shear lag model with the comparison of finite element analysis (FEA). The rationale is based on the replacement of the matrix between fiber ends with the fictitious fiber to maintain the compatibility of displacement and traction. It was found that the new model gives a good agreement with FEA results in the small fiber aspect ratio regime as well as that in the large fiber aspect ratio regime. It was found that the proposed simulation methodology for stress analysis is applicable to the complicated inhomogeneous solid for the investigation of micromechanical behavior.

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Dynamic Characterization of Sub-Scaled Building-Model Using Novel Optical Fiber Accelerometer System

  • Kim, Dae-Hyun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.31 no.6
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    • pp.601-608
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    • 2011
  • This paper presents the damage assessment of a building structure by using a novel optical fiber accelerometer system. Especially, a sub-scaled building model is designed and manufactured to check up the feasibility of the optical fiber accelerometer for structural health monitoring. The novel accelerometer exploits the moir$\acute{e}$ fringe optical phenomenon and two pairs of optical fibers to measure the displacement with a high accuracy, and furthermore a pendulum to convert the displacement into acceleration. A prototype of optical fiber accelerometer system has been successfully developed that consists of a sensor head, a control unit and a signal processing unit. The building model is also designed as a 4-story building with a rectangular shape of $200{\times}300$ mm of edges. Each floor is connected to the next ones by 6 steel columns which are threaded rods. Basically, a random vibration test of the building model is done with a shaker and all of acceleration data is successfully measured at the assigned points by the optical fiber accelerometer. The experiments are repeated in the undamaged state and the damaged state. The comparison of dynamic parameters including the natural frequencies and the eigenvectors is successfully carried out. Finally, the optical fiber accelerometer is proven to be prospective to evaluate dynamic characteristics of a building structure for the damage assessment.