• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.365-372
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• 2004

A new finite element model will be presented to analyze the nonlinear behavior of not only RC beams and slabs, but also RC beams strengthened by a patch repair. The numerical approach is based on the p-version degenerate shell element including theory of anisotropic laminated composites, theory of materially and geometrically nonlinear plates. In the nonlinear formulation of this model, the total Lagrangian formulation is adopted with large deflections and moderate rotations being accounted for in the sense of von Karman hypothesis. The material model is based on hardening rule, crushing condition, plate-end debonding strength model and so on. The Gauss-Lobatto numerical quadrature is applied to calculate the stresses at the nodal points instead of Gauss points. The validity of the proposed p-version finite element model is demonstrated through several numerical examples for the load-deflection curves, the ultimate loads, and the failure modes of reinforced connote slabs and RC beams bonded with steel plates or FRP plates compared with available experimental and numerical results.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2000.11a
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• pp.39-45
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• 2000

In recent years, composite materials such as fiber reinforced plastics (FRP) have gained considerable attention in the aircraft and automobile industries due to their light weight, high modulus and specific strength. In practice, control of chip formation appears to be the most serious problem since chip formation mechanism in composite machining has significant effects on the finished surface ［1,2,3,4,5］. Current study will discuss frequency analysis based on autoregressive (AR) time series model and process characterization in orthogonal cutting of a fiber-matrix composite materials. A sparsely distributed idealized model composite material, namely a glass reinforced polyester (GFRP) was used as workpiece. Analysis method employs a force sensor and the signals from the sensor are processed using AR time series model. The experimental correlation between the different chip formation mechanisms and model coefficients are established.(omitted)

• Journal of the Korean Society for Precision Engineering
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• v.25 no.9
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• pp.103-108
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• 2008

In-plane shear tests were performed to investigate the shear property change of FRP by plasma modification. Graphite/epoxy prepreg was used as a test material and plasma source was a microwave (2.4GHz) type. Plasma was induced by oxygen gas and its flow rate was kept $4{\sim}5$sccm with low vacuum state of $10^{-3}$ Torr. Prepreg was stacked unidirectionally ($[0^0]_8$) after plasma modification. Wettability was determined by measuring a contact angle. The results showed that the contact angle was decreased from $86^0$ to $45^0$ after plasma modification. Shear strength was also improved by ${\sim}10%$. SEM examination was made on the fracture surface and functional group produced by the plasma modification was investigated by XPS.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.177-182
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• 1999

사용한 보수.보강재, Rod, Fabric, Strand 형상을 콘크리트 구조물등에 보강재로 사용되어왔다. 이 재료는 해양환경하에서 내식성과 내구성을 갖는 철근및 철골대체용 복합소재와 초고층 경량 연속섬유보강 시멘트 복합재료는 탄소섬유, 아라미드섬유, 유리섬유등의 쉬트(sheet)형상을 신건재, 비자성, 비전도성, 전파차폐용 재료등에 사용할수있다. 그러나 FRP Rod를 내식성이 요구되는 철근 및 철골대체재로 사용할 경우에는 폴리머 매트릭스의 열화, 섬유와 폴리머간 계면 접착강도의 한계, 화재시 내화성, 보강재의 인발성등의 단점들을 갖고있다[1]. (중략)

• Structural Engineering and Mechanics
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• v.53 no.6
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• pp.1067-1081
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• 2015

This study investigates structural and mechanical behaviors of RC (Reinforced concrete) beams strengthened with tapered CFRP (Carbon fiber reinforced polymer) sheets having various configurations. Toward this goal, experiments are performed on RC beams strengthened with four layers of CFRP sheets and each layer of the CFRP is prepared to have different length. Experimental results show that tapered CFRPs have better strengthening effect than non-tapered CFRP sheets and maximum loads of the beams with tapered CFRPs are governed by the length of first CFRP layer rather than total length of CFRP layers. In addition, analyses are performed using FE (Finite Element) models including cohesive elements to predict debonding behaviors between FRP and concrete elements. The predicted results from the FE models show good agreement with the experimental results.

• Steel and Composite Structures
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• v.20 no.2
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• pp.413-429
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• 2016

A theoretical method to predict the interfacial stresses in the adhesive layer of reinforced concrete beams strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) plate is presented. The analysis provides efficient calculations for both shear and normal interfacial stresses in reinforced concrete beams strengthened with composite plates, and accounts for various effects of Poisson's ratio and Young's modulus of adhesive. Such interfacial stresses play a fundamental role in the mechanics of plated beams, because they can produce a sudden and premature failure. The analysis is based on equilibrium and deformations compatibility approach developed by Tounsi. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both the reinforced concrete beam and bonded plate. The paper is concluded with a summary and recommendations for the design of the strengthened beam.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.75-78
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• 2002

In this paper, we investigated the change of wettability, surface potential decay and surface resistivity caused by thermal-treated and plasma-treated FRP respectively for finding out the influence of electrical characteristics on the surface of polymer composites. For the change of wettability, the contact angle of thermal-treated specimen with the high temperature of 200$^{\circ}C$ increased. But that of plasma-treated specimen decreased. The characteristic of surface potential decay shows the tendency of the remarkable decrease on plasma-treated specimens, but no difference on thermal-treated specimen compared with untreated one. Also, for the surface resistivity, it shows the same trend compared with the change of contact angle. We can conclude that the degradation phenomena of epoxy surface are dominated by the induction of hydrophilicity and hydrophobicity.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.23-31
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• 1998

Kind 1 propeller shaft in ships is the shaft which is provided with effective measures against corrosion by sea water, or the shaft which is made of approved corrosion resistance materials. The propeller shaft other than specified above is Kind 2. Thus, this study is mainly concerned with the resistance to fatigue damage in sea water against stress concentrations due to the notches. The results obtained can be summarized as follows; (1) The stress increases with curing time, however, when the curing time reaches at 96 hours the stress becomes a constant value. The elongation decreases with curing time, however, when the curing time reaches at 48 hours the elongation becomes a constant value. Thus, in case of FRP coating on propeller shaft, it is necessary to cure for 48 hours at least. (2) The relation of $\sigma$$_n$-K$_t$ is to be classified into two parts, which is a part where fracture nominal stress, $\sigma$$_n$, decreases with increasing $K_t$, and a part where $\sigma$$_n$ is nearly constant independent of $K_t$. (3) According to a linear notch mechanics, the measure of severity controlling the fracture in notched FRP body is the notch root radius, $\rho$. The notched static strength of an arbitrary specimen will be estimated from $\sigma$$_{max}$ -1/$\rho$ curve. (4) Through the observation of cross section after fatigue test, the part of interface was kept good condition irrespective of loading conditions.

• Composites Research
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• v.26 no.4
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• pp.265-272
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• 2013

Fiber-reinforced plastic (FRP) is applied to fabricate the main structures of composite boats. Most of them are made from molds. These products deform after releasing from the mold and they also deform in high temperature environment. Therefore, experimental investigation and evaluation of deformation of laminated composite structures under various manufacturing and working conditions are necessary. The specimens of L-shape and curveshape were made from unsaturated polyester resin and fiberglass material. Input factors (independent variables) are percentage of hardener and manufacturing temperature and four levels of working temperature and output factor is the deformation which is measured on these specimens. From the results, it was observed that the higher the hardener rate and temperature, the lower the deformation. When the working temperature increased, the specimens showed great variations for the initial deformation values. Besides, the values of deformation or input factors could be predicted by regression equations.

• Composites Research
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• v.27 no.2
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• pp.59-65
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• 2014

Most of energy are obtained from oil, coal, and natural gas, most likely, fossil fuel which is limited throughout the world. Recently, high crude oil price, climate change, oil depletion, etc. are main reason to get attention to non-fossil energy including renewable energy in the world. In this study, we studied analysis and design of structure system composed of pultruded fiber reinforced polymer composite (PFRP) which has many advantages such as high specific strength and stiffness, high corrosion resistance and chemical resistance. For the design and construction of floating-type structure, PFRP structural members may be the first choice. Design of tracking-type floating PV generation structure was performed by using the results of the finite element analysis. The structure is fabricated and installed on the water surface. Before the installation of the structure, safety related problems associated with installation and operation are investigated using the finite element simulation and it was found that the structure is safe enough to resist externally applied loads.