• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.118-121
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• 2002

Polyvinylidene di-fluoride (PVDF) film sensor appeared to be practically useful for the structural health monitoring of composite materials and structures. PVDF film sensors were either attached to or embedded in the graphite/epoxy composite (CFRP) samples to detect the fatigue damage at the bondline of single-lap joints or the tensile failure of unidirectional laminates. PVDF sensors were sensitive enough to detect and determine the crack front in linear location since composites usually produce very energetic acoustic emission (AE). PVDF sensors are extremely cost-effective, as flexible as other plastic films, in low profile as thin as a few tens of microns, and have relatively wide-band response, all of which characteristics are readily utilized for the structural health monitoring of composite structures. Signals due to fatigue damage showed a characteristics of mode II (shear) type failure whereas those from fiber breakage at DEN notches showed that of mode I (tensile) type fracture.

• Composites Research
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• 제12권2호
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• pp.36-45
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• 1999

Since carbon fiber epoxy composite materials have excellent properties for structures due to their high specific strength, high modulus, high damping and low thermal expansion, the hollow shafts made of carbon fiber epoxy composites have been widely used for power transmission shafts for motor vehicles, spindles of machine tools and rollers for film manufacturing. However, the molded composite shafts are not usually accurate enough for mechanical machine elements, which require turning or grinding of composite hollow shafts. In this paper, the grinding characteristics of composite hollow shafts, which are flexible in the radial and circumferential directions, were investiaged experimentally and analytically with respect to the stacking angle, thickness and outer diameter.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2007년도 제32회 학술대회 초록집
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• pp.133-133
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• 2007

• Structural Engineering and Mechanics
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• 제55권4호
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• pp.719-742
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• 2015

This paper dealt the free vibration analysis of thick truncated conical composite sandwich shells with transversely flexible cores and simply supported boundary conditions based on a new improved and enhanced higher order sandwich shell theory. Geometries were used in the present work for the consideration of different radii curvatures of the face sheets and the core was unique. The coupled governing partial differential equations were derived by the Hamilton's principle. The in-plane circumferential and axial stresses of the core were considered in the new enhanced model. The first order shear deformation theory was used for the inner and outer composite face sheets and for the core, a polynomial description of the displacement fields was assumed based on the second Frostig's model. The effects of types of boundary conditions, conical angles, length to radius ratio, core to shell thickness ratio and core radius to shell thickness ratio on the free vibration analysis of truncated conical composite sandwich shells were also studied. Numerical results are presented and compared with the latest results found in literature. Also, the results were validated with those derived by ABAQUS FE code.

• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.173-179
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• 2018

Electrochemical characterization was conducted on poly(vinyl alcohol) (PVA)-ceramic composite (PVA-CC) separators for supercapacitor applications. The PVA-CC separators were fabricated by mixing various ceramic particles including aluminum oxide ($Al_2O_3$), silicon dioxide ($SiO_2$), and titanium dioxide ($TiO_2$) into a PVA aqueous solution. These ceramic particles help to create amorphous regions in the crystalline structure of the polymer matrix to increase the ionic conductivity of PVA. Supercapacitors were assembled using PVA-CC separators with symmetric activated carbon electrodes and electrochemical characterization showed enhanced specific capacitance, rate capability, cycle life, and ionic conductivity. Supercapacitors using the $PVA-TiO_2$ composite separator showed particularly good electrochemical performance with a 14.4% specific capacitance increase over supercapacitors using the bare PVA separator after 1000 cycles. With regards to safety, PVA becomes plasticized when immersed in 6 M KOH aqueous solution, thus there was no appreciable loss in tear resistance when the ceramic particles were added to PVA. Thus, the enhanced electrochemical properties can be attained without reduction in safety making the addition of ceramic nanoparticles to PVA separators a cost-effective strategy for increasing the ionic conductivity of separator materials for supercapacitor applications.

• Journal of Information Processing Systems
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• 제18권5호
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• pp.688-700
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• 2022

A composite bionic soft gripper integrated with electromagnets and magneto-active elastomers is designed by combining the structure of the human hand and the snake's behavior of enhancing friction by actively adjusting the scales. A silicon-based polymer containing magnetized hard magnetic particles is proposed as a soft finger, and it can be reversibly bent by adjusting the magnetic field. Experiments show that the length, width, and height of rectangular soft fingers and the volume ratio of neodymium-iron-boron have different effects on bending angle. The flexible fingers with 20 vol% are the most efficient, which can bend to 90° when the magnetic field is 22 mT. The flexible gripper with four fingers can pick up 10.51 g of objects at the magnetic field of 105 mT. In addition, this composite bionic soft gripper has excellent magnetron performance, and it can change surface like snakes and operate like human hands. This research may help develop soft devices for magnetic field control and try to provide new solutions for soft grasping.

• 한국항공우주학회지
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• 제36권8호
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• pp.734-739
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• 2008

본 논문에서는 미시 및 중시 역학의 2-단계 해석 전략을 채택하여 유연직물 복합재료의 기계적 거동을 예측하였다. 미시역학에서는 섬유다발의 유효물성치를 계산하였고 그 결과를 이용해 중시역학에서 유연직물복합재료의 인장탄성계수를 예측하였다. 중시역학 해석 과정에서는 섬유다발의 회전 및 전단 대변형에 의한 기하학적 비선형성을 고려하기 위하여 사용자 정의 부프로그램을 개발하여 ABAQUS 내에 삽입하였다. 해석결과, 인장하중을 받는 유연직물복합재료의 응력-변형률은 비선형 거동을 보였고, 계산된 유효탄성계수는 시험값과 잘 일치하는 것으로 나타났다.

• Composites Research
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• 제27권6호
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• pp.242-247
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• 2014

전기활성고분자의 종류 중 하나인 유전성 탄성체의 거동에 대응할 수 있는 유연전극 제조에 대한 연구를 수행하였다. 전도성 고분자(PEDOT:PSS)에 가소제 역할을 하는 자이리톨(Xylitol)을 첨가하여 기계적 특성을 평가하였다. 자이리톨을 첨가한 전극의 유연성을 확인하기 위해 실리콘 시편에 전극을 도포하여 인장시험을 수행하였다. 자이리톨을 70 wt% 첨가한 조건에서 연신률이 크게 증가함을 확인하였고 실리콘 거동에 큰 영향을 미치지 않는 것을 확인하였다. 또한, 전극과 실리콘의 접착성을 향상시키기 위해 표면조도가 다른 실리콘 필름을 제작하였으며 사포 #120으로 처리한 시편에서 실리콘 필름과 전극의 접착성이 향상됨을 확인하였다.

• Steel and Composite Structures
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• 제3권2호
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• pp.111-122
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• 2003

The paper presents a model for analysing the shear-lag effect on the slab of twin-girder composite decks subjected to static actions, support settlements and concrete shrinkage, which are the main actions of interest in composite bridge design. The proposed model includes concrete creep behaviour and shear connection flexibility. The shear-lag in the slab is accounted for by means of a new warping function. The considered actions are then applied to a realistic bridge deck and their effects are discussed. The proposed method is utilised to determine the slab effective widths for three different width-length ratios of the deck. Finally, a comparison between the results obtained with the Eurocode EC4-2 and those obtained with the proposed model is performed.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.147-150
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• 2002

For lightweight and flexible structures, it is important to suppress the vibrations induced by interactions between fluid and structures. This paper presents the PPF/Adaptive control of the vortex-induced vibration of composite beam with rigid cylinder in which the fluid force is considered as an external excitation on the structure. For the problems considered here, the excitation frequency (vortex-shedding frequency) is assumed to be equal to the natural frequency of the structure. A pair of piezoceramic devices attached bottom of the composite structure was used as actuators. Simulation and experiment were carried out with the designed controller and effectiveness of the PPF/Adaptive PPF control was verified by both experimental and simulation results.