• Advanced Composite Materials
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• 제18권4호
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• pp.327-338
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• 2009

In this paper, through an evaluation process conducted on several designs of mini-LIPCA (Lightweight Piezo-Composite curved Actuator), an optimal design of a mini-LIPCA has been proposed. Comparing with the LIPCA-C2, the design of the mini-LIPCA comes with reduced overall size and a thinner active layer. Since a variation in the number and lay-up of fiber composite layers may strongly affect the performance of the device, one is able to configure several designs of mini-LIPCA. The evaluation process is then followed in order to determine a configuration which characterizes the possibly optimal performance. That is, a design of a mini-LIPCA is said to be optimal if it is capable of producing a maximum out-of-plane displacement. The size of the LIPCA to be investigated was selected to be $10\;mm\;{\times}\;20\;mm$ in which the thickness of PZT plate is about 0.1 mm. The thickness of glass/epoxy and carbon/epoxy are about 0.09 mm and 0.1 mm, respectively. The evaluation process has been conducted thoroughly, i.e., analytical estimation, numerical approximation and the experimental measurement are all involved. Firstly, the design equation was used to calculate essential parameters of proposed lay-up configurations. Secondly, ANSYS, a commercial FEA package, was utilized to estimate displacement outputs of the actuators upon being excited. Finally, experimental measurements were able to verify the predicted results.

• Composites Research
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• 제31권6호
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• pp.311-316
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• 2018

In the present study, the effect of GO in damping capacity of CF/epoxy laminates was studied via free vibration analysis. The composite laminates were manufactured by using vacuum assisted resin transfer molding technique. The damping properties of the prepared hybrid composites were determined in terms of natural frequency and damping ratio in free vibration test. The foremost aspire of this investigation was to compare the vibration properties i.e. natural frequency and modal damping of the prepared composites with the numerical results. The numerical study was carried out via FEA using $ANSYS^{TM}$ workbench software. The parametric study of the numerical models was also studied considering the beam free length and the beam thickness. It was found that the incorporation of GO enhanced the damping capacity of the composite and the variation of natural frequencies in mode1varied by 2-5% compared to the experimental study.

• Structural Engineering and Mechanics
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• 제67권4호
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• pp.403-415
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• 2018

In the present study, nonlinear dynamic response of polymer-CNT-fiber multiscale nanocomposite plate resting on elastic foundations in thermal environments using the finite element method is performed. In this regard, the governing equations are derived based on Inverse Hyperbolic Shear Deformation Theory and von $K{\acute{a}}rm{\acute{a}}n$ geometrical nonlinearity. Three type of distribution of temperature through the thickness of the plate namely, uniform linear and nonlinear are considered. The considered element is C1-continuous with 15 DOF at each node. The effective material properties of the multiscale composite are calculated using Halpin-Tsai equations and fiber micromechanics in hierarchy. The carbon nanotubes are assumed to be uniformly distributed and randomly oriented through the epoxy resin matrix. Five types of impulsive loads are considered, namely the step, sudden, triangular, half-sine and exponential pulses. After examining the validity of the present work, the effects of the weight percentage of SWCNTs and MWCNTs, nanotube aspect ratio, volume fraction of fibers, plate aspect, temperature, elastic foundation parameters, distribution of temperature and shape of impulsive load on nonlinear dynamic response of CNT reinforced multi-phase laminated composite plate are studied in details.

• 한국정밀공학회지
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• 제22권10호
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• pp.121-128
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• 2005

The research on electromagnetic shielding has been advanced for military applications as well as for commercial products. Utilizing the reflective properties and absorptive properties of shielding material, the replied signal measured at the rear surface or at the signal source can be minimized. The shielding effect was obtained from materials having special absorptive properties and structural characteristics such as stacking sequence. Recently researchers studied the electromagnetic properties of nano size particles. In this research {glass fiber}/{epoxy}/{nano particle} composites(GFR-Nano composites) was fabricated using various nano particles, and their properties in electromagnetic shielding were compared. For the visual observation of the nano composite materials, SEM(Scanning Electron Microscope) and TEM(Transmission Electron Microscope) were used. For the measurement of electromagnetic shielding, HP8719ES S-parameter Vector Network Analyser System was used on the frequency range of 8 GHz${\~}$12GHz. Among the nano particles, carbon black and Multi-Walled Carbon Nano-Tube (MWCNT) revealed outstanding electromagnetic shielding. Although silver nano particles (flake and powder) were expected to have effective electromagnetic shielding due to their excellent electric conductivities, test results showed little shielding characteristics.

• Composites Research
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• 제16권2호
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• pp.68-73
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• 2003

Fragmentation 시험법과 전기저항 측정을 통하여 탄소 및 SiC 섬유강화 에폭시 복합재료의 계면물성과 섬유파단에 대한 전기적 감지능을 연구하였다. 섬유 함침 각이 증가함에 따라서 계면전단강도는 감소하였고, 섬유파단에 의한 전기저항도 값이 무한대로 증가하는 시간은 길어졌다. 높은 함침 각에서 전기저항도의 초기 기울기는 급격히 증가한 반면. 낮은 각에서는 점차적으로 증가하였다. 또한 낮은 함침각의 두 섬유 모두에서 stress whitening pattern을 뚜렷하게 관찰할 수 있었지만, 높은 함침 각에서는 그렇지 못했다. 섬유 함침 각이 감소함에 따라서 섬유 파단 간격과 debonding된 길이는 두 섬유 모두에서 증가하였다. 본 연구에서 사용한 electro-micromechanical 시험법은 전도성 섬유강화 복합재료의 섬유 함침 각에 따른 계면 감지능 측정을 위해서 비파괴적 평가방법으로 실행 가능하였다.

• 상하수도학회지
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• 제37권4호
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• pp.203-214
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• 2023

In this study, the physical properties and fracture characteristics according to the tensile load are evaluated on the materials of the polymeric filler and carbon fiber-based composite sleeve technique. The polymeric filler and the composite sleeve technique are applied to areas where the pipe body thickness is reduced due to corrosion in large-diameter water pipes. First, the tensile strength of the polymeric filler was 161.48~240.43 kg_f/cm², and the tensile strength of the polyurea polymeric filler was relatively higher than that of the epoxy. However, the tensile strength of the polymeric filler is relatively very low compared to ductile cast iron pipes(4,300 kg_f/cm²<) or steel pipes(4,100 kg_f/cm²). Second, the tensile strength of glass fiber, which is mainly used in composite sleeves, is 3,887.0 kg_f/cm², and that of carbon fiber is up to 5,922.5 kg_f/cm². The tensile strengths of glass and carbon fiber are higher than ductile cast iron pipe or steel pipe. Third, when reinforcing the hemispherical simulated corrosion shape of the ductile cast iron pipe and the steel pipe with a polymeric filler, there was an effect of increasing the ultimate tensile load by 1.04 to 1.06 times, but the ultimate load was 37.7 to 53.7% compared to the ductile cast iron or steel specimen without corrosion damage. It was found that the effect on the reinforcement of the corrosion damaged part was insignificant. Fourth, the composite sleeve using carbon fiber showed an ultimate load of 1.10(0.61T, 1,821.0 kg_f) and 1.02(0.60T, 2,290.7 kg_f) times higher than the ductile cast iron pipe(1,657.83 kg_f) and steel pipe(2,236.8 kg_f), respectively. When using a composite sleeve such as fiber, the corrosion damage part of large-diameter water pipes can be reinforced with same level as the original pipe, and the supply stability can be secured through accident prevention.

• 접착 및 계면
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• 제23권1호
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• pp.1-7
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• 2022

풍력블레이드가 대형화되면서 유리섬유 복합재료(GFRP)와 탄소섬유 복합재료(CFRP)를 혼용하여 제작하고 있고, 이 때 두 가지 이종재료 간의 접착특성에 대한 연구가 활발히 진행되고 있다. 본 연구에서는 에폭시 접착제 내 탄소나노튜브 함량 및 경화 시 습도의 차이에 따른 접착강도의 변화를 평가하였다. 탄소나노튜브의 함량이 다른 에폭시 접착제를 활용하여 GFRP와 CFRP를 접착하였고, 경화 시 습도에 따른 특성의 변화를 알아보기 위해 접착강도를 평가하였다. 탄소나노튜브 함량에 따른 변화를 알아보기 위해 접착제에 들어가는 탄소나노튜브의 함량을 0, 0.1, 0.3, 0.5, 1 wt%로 나누어 단일 랩 전단 시험을 진행하였고, 습도 조건에 따른 변화를 확인하기 위해 항온항습기로 습도를 20, 50, 80% 조건으로 나누어 접착제를 경화시킨 후 단일 랩 전단 시험을 진행하였다. 실험결과 에폭시 접착제에 탄소나노튜브를 넣음으로써 접착특성이 향상됨을 확인하였지만 함량이 과도하게 많을 때에는 접착력이 줄어드는 것을 확인하였다. 또한 습도가 증가할수록 접착특성이 변하지 않음을 확인할 수 있었다.

• Composites Research
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• 제22권5호
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• pp.8-14
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• 2009

유리섬유 강화 CNT-에폭시 나노복합재료의 계면특성은 미세역학적 시험법과 젖음성 측정을 통하여 평가하였다. CNT-에폭시 나노복합재료의 접촉저항은 전기적 접촉부가 일정하게 점차적으로 증가하는 경사형 (gradient) 시편으로 측정되었다. CNT-에폭시나노복합재료의 접촉저항은 2-점법 대신에 4-점법을 사용하여 평가하였다. 불균일한 표면에 존재하는 소수성 영역 때문에 CNT-에폭시 나노복합재료의 어떤 부분은 초소수성보다는 다소 낮은 접촉각인 120도를 가졌다. 표면처리된 유리섬유는 에칭된 섬유 표면의 흠이 있지만 인장 강성도는 약간의 변화가 나타나는 반면에, 인장강도는 현저하게 감소하였다. 에칭된 유리섬유와 CNT-에폭시 나노복합재료는 표면 에너지와 거친 정도가 증가함으로써, 계면전단강도가 증가되었다 열역학적 에너지 일인 $W_a$가 증가함에 따라, 기계적 계면전단강도와 겉보기 강성도 모두 상호일치하게 증가를 보여주었다.

• 한국추진공학회지
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• 제25권6호
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• pp.74-86
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• 2021

복합재 격자구조체는 요구 하중을 최소한의 무게 및 두께로 지지하는 구조체로, 고강도 탄소섬유에 에폭시 수지를 함침시켜 필라멘트 와인딩 공법으로 제작된다. 구조적으로 반드시 필요한 부분만을 적층 및 제작하므로 항공기 동체, 위성발사체 및 유도무기 등에 적용하여 경량화를 극대화 할 수 있다. 본 논문에서는 대형 원통형 및 콘형 복합재 격자구조체의 설계, 해석, 제작 및 평가까지 전 순기에 해당하는 복합재 격자구조체 개발 및 평가를 수행하였다. 실제 발사체 및 유도무기에 적용이 가능하도록 직경 2,600 mm, 길이 2,000 mm의 원통형 격자구조체와 상단 직경 1,300 mm, 하단 직경 2,500 mm, 길이 900 mm의 콘형 격자구조체를 개발하였으며, 하중시험을 통해 대형 복합재 격자구조체의 성능을 평가하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.223-226
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• 2002

To maximize the productivity in machining molds and dies, machine tools should operate at high speeds. However, the productivity of mold manufacturing has not increased significantly because CNC milling machines have massive slides, which do not allow rapid acceleration and deceleration during the frequent starts/stops encountered in machining molds and dies. This paper presents the use of composites for these slides to overcome this limitation. The vertical and horizontal slides of a large CNC machine were constructed by bonding high-modulus carbon-fiber epoxy composite sandwiches to welded steel structures using adhesives. These composite structures reduced the weight of the vertical and horizontal slides by 34% and 26%, respectively, and increased damping by 1.5 to 5.7 times without sacrificing the stiffness. Without much tuning, this machine had a positional accuracy of $\pm5\mu\textrm{m}$ per 300 m of the slide displacement.