• Smart Structures and Systems
• /
• 제26권2호
• /
• pp.157-174
• /
• 2020

The guided wave technique is commonly used in structural health monitoring as the guided waves can propagate far in the structures without much energy loss. The guided waves are conventionally generated by the surface-mounted piezoelectric wafer active sensor (PWAS). However, there is still lack of understanding of the wave propagation in layered structures, especially in structures made of anisotropic materials such as carbon fiber reinforced polymer (CFRP) composites. In this paper, the Rayleigh-Lamb wave strain tuning curves in a PWAS-mounted unidirectional CFRP plate are analytically derived using the normal mode expansion (NME) method. The excitation frequency spectrum is then multiplied by the tuning curves to calculate the frequency response spectrum. The corresponding time domain responses are obtained through the inverse Fourier transform. The theoretical calculations are validated through finite element analysis and an experimental study. The PWAS responses under the free, debonded and bonded CFRP conditions are investigated and compared. The results demonstrate that the amplitude and travelling time of wave packet can be used to evaluate the CFRP bonding conditions. The method can work on a baseline-free manner.

• Steel and Composite Structures
• /
• 제30권3호
• /
• pp.271-280
• /
• 2019

In this paper, numerical and experimental assessments have been conducted in order to investigate the capability of using CFRP for the seismic capacity improvement and relocation of plastic hinge in reinforced concrete connections. Two scaled down exterior reinforced concrete beam to column connections have been used. These two connections from a strengthened moment frame have been tested under uniformly distributed load before and after optimization. The results of experimental tests have been used to verify the accuracy of numerical modeling using computational ABAQUS software. Application of FRP plate on the web of the beam in connections to improve its capacity is of interest in this paper. Several parametric studies were carried out for CFRP reinforced samples, with different lengths and thicknesses in order to relocate the plastic hinge away from the face of the column.

• Advanced Composite Materials
• /
• 제17권4호
• /
• pp.359-372
• /
• 2008

The moisture absorption behavior of carbon fiber-reinforced plastic (CFRP) and its effect on dimensional stability were examined. Moisture diffusivity in CFRP was determined by measuring a specimen's weight during the moisture absorption test. Three types of CFRP specimens were prepared: a unidirectionally reinforced laminate, a quasi-isotropic laminate and woven fabric. Each CFRP was processed into two geometries - a thin plate for determination of diffusivity and a rod with a square cross-section for the discussion of two-dimensional diffusion behavior. By solving Fick's law expanded to 3 dimensions, the diffusivities in the three orthogonal directions were obtained and analyzed in terms of the anisotropy of CFRP moisture diffusion. Coefficients of moisture expansion (CMEs) were also obtained from specimen deformation caused by moisture absorption. During moisture absorption, the specimen surfaces showed larger deformation near the edges due to the distribution of moisture contents. This deformation was reasonably predicted by the finite element analysis using experimentally determined diffusivities and CMEs. For unidirectional CFRP, the effect of the fiber alignment on CME was analyzed by micromechanical finite element analysis (FEA) and discussed.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
• /
• pp.211-214
• /
• 2001

Electronic Speckle Pattern Interferometry(ESPI) is one of optical technique to measure displacement precisely, uses CCD camera to show result image in real time. General ESPI system measures in-plane or out-of-plane displacement. Shearography is one of electronic speckle pattern interferometric methods which allow full-field observation of surface displacement derivatives and it is robust in vibration. The shearography provides non-contacting technique of evaluating defects nondestructively. In this study, the shearography was used to evaluate defects in Carbon Fiber Reinforced Plastic(CFRP). Various sizes of artificial defects were embedded in various depths of woven CFRP plate. Effects due to the variation of size and depth of defects were evaluated in this study.

• 한국정밀공학회지
• /
• 제33권6호
• /
• pp.447-452
• /
• 2016

The simulation of Carbon fiber reinforced polymer (CFRP) machining facilitates the selection of optimal cutting parameter for high machining efficiency and better surface quality. In this study, This paper proposes a dual-dexel model to represent the fiber laminate with computational geometry method to calculate the fiber length removed per revolution and fiber cutting angles. A flat end milling simulation software is developed in C# to simulate and display the CFRP milling process. During simulation, fiber lengths, fiber cutting angle and engaged cutting angle can be displayed in real-time. A CFRP plate with different angles in different layer is used to compare the simulation results.

• 한국신뢰성학회:학술대회논문집
• /
• 한국신뢰성학회 2002년도 정기학술대회
• /
• pp.245-251
• /
• 2002

Electronic Speckle Pattern Interferometry(ESPI) is one of optical technique to measure displacement precisely, uses CCD camera to show result image in real time. General ESPI system measures in-plane or out-of-plane displacement. Shearography is one of electronic speckle pattern interferometric methods which allow full-field observation of surface displacement derivatives and it is robust in vibration. The shearography provides non-contacting technique of evaluating defects nondestructively In this study, the shearography was used to evaluate defects in Carbon Fiber Reinforced Plastic(CFRP). Various sizes of artificial defects were embedded in various depths of woven CFRP plate. Effects due to the variation of size and depth of defects were evaluated in this study.

• 콘크리트학회논문집
• /
• 제21권6호
• /
• pp.681-688
• /
• 2009

철도교량은 일반적으로 공용기간동안 진동과 충격에 의한 구조적 영향을 받는다. 이와 같은 이유로 내하력 증진을 위한 보강성능 검토 시 철도교에 작용하는 외부하중에 효율적으로 저항할 수 있는 보강성능이 요구된다. 이 연구에서는 철도교의 공용 중 진동 및 충격하중에 효율적으로 저항할 수 있는 보강공법으로써 NSM 보강공법을 제안하였다. 이는 기존 탄소섬유외부부착 공법에 비해 부착성능 및 보강성능이 우수한 공법이다. NSM 보강공법은 현재 다양한 실험적 연구들이 진행되고 있으나, 실교량으로의 범용적인 적용을 위해서는 보강설계에 필요한 합리적인 보강비 산정이 필수적이다. 이를 위해, 이 연구에서는 재료적 및 기하학적 불확실성이 반영된 확률 신뢰도기반 NSM 보강비 산정방법을 제안하여 임계보강비를 산정하고자 한다. 이를 위해, Monte Carlo Simulation(MCS) 기법으로 도출된 재료 및 단면치수에 대한 불확실성 특성을 내부저항모멘트 설계식에 반영하여, 외부활하중의 불확실성 특성이 반영된 외부하중모멘트에 대한 안전도 평가를 수행하였으며, 목표신뢰성지수 3.5를 만족할 수 있도록 하는 CFRP 플레이트의 임계보강비를 산출하였다.

• 한국안전학회지
• /
• 제29권5호
• /
• pp.15-21
• /
• 2014

The aim of this work is conduct the study on light weight and structural performance improvement of the composite wind power blade. GFRP (Glass Fiber Reinforced Plastic) pre-empted by CFRP(Carbon Fiber Reinforced Plastic), the major material of wind power blade, was identified the superiority of mechanical performance through the tensile and fatigue test. SENT(Single Edge Notched Tension) specimen fracture test was conducted on the specimen that laminated together 2 ply CFRP with 4 ply GFRP through DIC(Digital Image Correlation) analysis. The SENT specimen thickness and $a_0/W$ ratio is 1.45 mm and 0.2, respectively. The fracture test accomplished with displacement control with 0.1 mm/min at the room temperature. The experimental apparatus used for the fracture test consisted of a 50kN universal dynamic tester and CCD camera connected to a personal computer (PC), which was used to record images of the specimen surface. Following data acquisition, the images and load-displacements were transferred to the PC, on which the DIC software was implement. The experiment and DIC analysis results show that CFRP/GFRP laminated composite exhibits improvement of the strength, compared with that of the existing blade material. This study shows the result that the strength of CFRP rotor blade of wind turbine satisfies through the experimental and DIC method.

• 한국구조물진단유지관리공학회 논문집
• /
• 제13권6호통권58호
• /
• pp.115-125
• /
• 2009

건축물의 보수 보강 시 섬유보강 폴리머를 이용한 부착공법을 이용한 보수 보강이 행해지고 있으며, 특히 CFRP(carbon fiber reinforced polymer)는 이러한 RC 구조부재의 보강재로 널리 활용되고 있다. 그러나 외부 환경적 요인에 의해 열화되는 즉, 동결융해 환경이 RC 보에서의 CFRP 보강성능에 미치는 영향에 관한 연구는 전무한 실정이다. 따라서 본 연구에서는 AE 기법을 통해 CFRP와 RC 부재 내부의 손상진전에 따라 발생하는 AE 신호를 계측함으로써 CFRP로 보강 후 동결융해에 의해 열화된 RC 구조물의 파괴기구 규명을 위한 기초자료를 마련하고자 한다.

• 콘크리트학회논문집
• /
• 제19권2호
• /
• pp.225-231
• /
• 2007

최근 건설 산업에서 FRP는 재료적 장점들 때문에 구조물의 보강재로서 높은 관심을 모으고 있다. 본 연구에서는 CFRP 보강량에 따른 철근콘크리트 보의 구조적 거동과 보강된 CFRP 종류에 따른 보의 연성에 대해 연구한 것이다. 실험에서 보강량을 증가시켜 실험했을 때 실험체를 겹 보강하는 것보다는 폭 보강하는 것이 더 효율적이었다. CFRP로 보강된 보의 파괴에서는 휨 파괴를 일으키면서 취성적인 양상을 보였다. 또한 에너지 비 측면에서 보의 대부분이 취성 파괴로 분류되었다. CFRP 플레이트에 비해 쉬트의 에너지 비가 전체적으로 50%를 넘고 겹 보강을 하지 않은 실험체는 약 70% 정도로 나타났다.