• 대한토목학회논문집
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• 제39권6호
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• pp.675-689
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• 2019

자가응력 및 자가손상 감지능력을 모두 가지는 스마트 콘크리트의 개발은 아직까지 손상 감지 능력에 대한 원인 규명이 명확하지 않아 어려운 현실이다. 따라서, 본 연구에서는 매트릭스 강도, 섬유 형식 및 보강량이 강섬유 보강 시멘트 복합재료의 인발시 전기저항에 미치는 영향을 평가하였다. 실험으로부터 섬유와 매트릭스 사이 계면에서의 탈착으로 전기저항률이 감소한다는 사실을 알 수 있었다. 섬유와 매트릭스 사이 계면 부착강도가 높을수록 더 큰 전기저항률의 감소를 유발하였다. 따라서, 고강도 매트릭스, 황동 도금된 강섬유 그리고 변형된 강섬유를 사용시 높은 계면부착강도를 유발하고 그 결과 더 큰 전기저항률 감소를 유발하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.216-219
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• 2002

Conventional piezoelectric lead-zirconate-titanate (PZT) senor has high sensitivity, but it is very brittle. Recently polymer films such as polyvinylidene fluoride (PVDF) have been used use as a sensor. The advantages of PVDF are the flexibility and mechanical toughness. Simple process and possible several shapes are also additional advantages. PVDF sensor can be directly embedded and attached to a structure. In this study, PVDF sensor was embedded in single glass fiber/epoxy composites whereas PZT sensor with AE was attached to single fiber composites (SFC). Piezoelectric sensor responds to interfacial damage of SFC. The signals measured by PVDF sensor were compared to PZT sensor. PZT sensor detected the signals of fiber fracture, matrix crack, interfacial debonding and even sensor delamination, whereas PVDF sensor only detected fiber fracture signals so far, because PZT sensor is much more sensitive than current PVDF sensor. Wave voltage of fiber fracture measured by PVDF sensor was lower than that of PZT sensor, but the results of fast Fourier transform (FFT) analysis were same. Wave velocity using two PZT sensors was also studied to know the internal and surface damage effect of epoxy specimens.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.95-102
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• 2004

변형률과 파손신호를 동시에 계측하기 위하여 이중복조기를 갖는 광섬유 브래그 격자센서시스템을 제안하였다. 이중복조기는 가변 패브리-페로 필터를 사용하여 변형률과 같이 변화가 큰 저주파신호를 측정하는 복조기와 수동 마흐-젠더 간섭계를 사용하여 파손신호나 충격신호와 같이 미세한 크기의 고주파 신호를 측정하는 복조기로 구성된다. 제안된 광섬유 브래그 격자센서시스템을 이용하여 인장하중을 받는 직교적층 복합재 구조물의 변형률과 파손신호를 동시에 계측할 수 있었다. 하나의 광섬유브래그격자센서로 측정한 변형률과 파손신호를 분석한 결과, 복합재 시편의 90도 층에서 모재균열이 발생할 때 급격한 변형률 변이가 유발되고, 최대 수백킬로헤르쯔에 이르는 주파수 성분을 가진 진동신호가 발생함을 알 수 있었다.

• 대한토목학회논문집
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• 제28권1A호
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• pp.115-123
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• 2008

최근 섬유강화 복합재료의 특성예측은 많은 공학자들에게 관심의 대상이 되고 있으며, 섬유강화 복합재료의 특성을 예측하기 위한 다양한 이론적, 수치적 방법들이 제안되고 있다. 본 연구에서는 복합재료내 구성요소를 고려한 Ju and Zhang (2001)의 미세역학 모델을 개선하고 원형섬유와 매트릭스간의 점진적인 손상을 고려하여 원형섬유강화 복합재료의 탄소성거동 및 점진적 손상해석을 위한 미세역학 모델을 개발하였다. 제안된 해석모델을 이용하여 다양한 수치해석을 통해 원형섬유강화 복합재료의 탄소성거동 및 점진적 손상을 예측하였고 손상을 고려하지 않은 모델과의 비교를 통하여 점진적 손상이 복합재료의 탄소성거동에 미치는 영향을 검토하였다.

• Structural Engineering and Mechanics
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• 제51권1호
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• pp.89-110
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• 2014

In this study, two beam-column elements based on the Elasto-Fiber element theory for reinforced concrete (RC) element have been developed and compared with each other. The first element is based on Elasto Fiber Approach (EFA) was initially developed for steel structures and this theory was applied for RC element in there and the second element is called as Fiber & Bernoulli-Euler element approach (FBEA). In this element, Cubic Hermitian polynomials are used for obtaining stiffness matrix. The beams or columns element in both approaches are divided into a sub-element called the segment for obtaining element stiffness matrix. The internal freedoms of this segment are dynamically condensed to the external freedoms at the ends of the element by using a dynamic substructure technique. Thus, nonlinear dynamic analysis of high RC building can be obtained within short times. In addition to, external loads of the segment are assumed to be distributed along to element. Therefore, damages can be taken account of along to element and redistributions of the loading for solutions. Bossak-${\alpha}$ integration with predicted-corrected method is used for the nonlinear seismic analysis of RC frames. For numerical application, seismic damage analyses for a 4-story frame and an 8-story RC frame with soft-story are obtained to comparisons of RC element according to both approaches. Damages evaluation and propagation in the frame elements are studied and response quantities from obtained both approaches are investigated in the detail.

• Smart Structures and Systems
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• 제9권5호
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• pp.461-472
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• 2012

This study proposes an optics-based active sensing system for continuous monitoring of underground pipelines in nuclear power plants (NPPs). The proposed system generates and measures guided waves using a single laser source and optical cables. First, a tunable laser is used as a common power source for guided wave generation and sensing. This source laser beam is transmitted through an optical fiber, and the fiber is split into two. One of them is used to actuate macro fiber composite (MFC) transducers for guided wave generation, and the other optical fiber is used with fiber Bragg grating (FBG) sensors to measure guided wave responses. The MFC transducers placed along a circumferential direction of a pipe at one end generate longitudinal and flexural modes, and the corresponding responses are measured using FBG sensors instrumented in the same configuration at the other end. The generated guided waves interact with a defect, and this interaction causes changes in response signals. Then, a damage-sensitive feature is extracted from the response signals using the axi-symmetry nature of the measured pitch-catch signals. The feasibility of the proposed system has been examined through a laboratory experiment.

• 한국건축시공학회지
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• 제8권5호
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• pp.43-51
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• 2008

This study examines shear capacity performance and structural characteristics of reinforced concrete beam using carbon fiber sheet(CFS), g)ass fiber sheet(GFS), glass fiber steel plate(GSP) and carbon fiber bar CB) which are reinforcing materials for reinforced concrete beam in order to produce similar condition to repair and reinforce actual structure and aims to provide data available In designing and constructing reinforced concrete structures under the structural damage. This study obtains the following conclusions. After considering the shear experiment results. it was indicated that the CB reinforced test object was the best in the shear capacity improvement and ductility capacity as it was contained in the concrete and was all operated, Also, GFS reinforced test object indicated the reduced flexural capacity but good shear capacity. GSP reinforced test object had bigger reinforcing strength than other reinforcing test objects. On the other hand, it showed the lowest reinforcement effect as compared section thickness of reinforced material because it showed the bigger relativity a section thickness of reinforced material. If the adherence to the concrete is improved, it will seem to show bigger reinforcement effect.

• Coupled systems mechanics
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• 제11권1호
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• pp.15-32
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• 2022

The comprehensive understanding of the fiber reinforced polymer behavior requires the use of advanced non-destructive testing methods due to its heterogeneous microstructure and anisotropic mechanical proprieties. In addition, the material response under load is strongly associated with manufacturing defects (e.g., voids, inclusions, fiber misalignment, debonds, improper cure and delamination). Such imperfections and microstructures induce various damage mechanisms arising at different scales before macrocracks are formed. The origin of damage phenomena can only be fully understood with the access to underlying microstructural features. This makes X-ray Computed Tomography an appropriate imaging tool to capture changes in the bulk of fibrous materials. Moreover, Digital Volume Correlation (DVC) can be used to measure kinematic fields induced by various loading histories. The correlation technique relies on image contrast induced by microstructures. Fibrous composites can be reinforced by different fiber architectures that may lead to poor natural contrast. Hence, a priori analyses need to be performed to assess the corresponding DVC measurement uncertainties. This study aimed to evaluate measurement resolutions of global and regularized DVC for glass fiber reinforced polymers with different fiber architectures. The measurement uncertainties were evaluated with respect to element size and regularization lengths. Even though FE-based DVC could not reach the recommended displacement uncertainty with low spatial resolution, regularized DVC enabled for the use of fine meshes when applying appropriate regularization.

• 한국의류학회지
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• 제40권6호
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• pp.979-993
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• 2016

Mongolian cashmere sliver, yarn, and fabric were dyed and bleached with a solution of ascorbic acid and iron sulfate at $70^{\circ}C$, and then dyed using natural indigo powder at the dyeing temperature of $25^{\circ}C$ to $90^{\circ}C$ for 15-90 minutes using the IR dyeing machine. K/S values of bleached samples decreased significantly when dyed above $70^{\circ}C$ dyeing temperature for a longer dyeing time. Bleached cashmere fabric showed a greater loss of tensile strength than unbleached cashmere fabric, even when the samples were dyed at $40^{\circ}C$. With a higher dyeing temperature, yarns lost fullness, became thinner, and the pores between the yarns were enlarged. The x-ray diffraction pattern exhibited a prominent increase in crystallinity and the protein assay indicated a loss of protein in the bleached sample dyed at $90^{\circ}C$. Thinning of scales, fractured or raised tip of scales, and roughness on the entire surface of the fiber were also observed. The results indicate that bleaching and high temperature dyeing cause a serious damage to cashmere fibers. In addition, bleaching and high temperature dyeing cause significant fiber damage. Natural indigo dyeing using low temperature dyeing is recommended to produce blue color cashmere.

• Structural Monitoring and Maintenance
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• 제4권1호
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• pp.1-15
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• 2017

Installation of sensors networks for continuous in-service monitoring of structures and their efficiency conditions is a current research trend of paramount interest. On-line monitoring systems could be strategically useful for road infrastructures, which are expected to perform efficiently and be self-diagnostic, also in emergency scenarios. This work researches damage detection in composite concrete-steel structures that are typical for highway overpasses and bridges. The techniques herein proposed assume that typical damage in the deck occurs in form of delamination and cracking, and that it affects the peak power spectral density of dynamic curvature. The investigation is performed by combining results of measurements collected by long-gauge fiber optic strain sensors installed on monitored structure and a statistic approach. A finite element model has been also prepared and validated for deepening peculiar aspects of the investigation and the availability of the method. The proposed method for real time applications is able to detect a documented unusual behavior (e.g., damage or deterioration) through long-gauge fiber optic strain sensors measurements and a probabilistic study of the dynamic curvature power spectral density.