• Structural Engineering and Mechanics
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• v.66 no.2
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• pp.229-235
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• 2018

This study investigated the behaviour of the simply supported hollow steel tube (HST) beams, either concrete filled or unfilled when strengthened with carbon fibre reinforced polymer (CFRP) sheets. Eight specimens with varied tubes thickness (sections classification 1 and 3) were all tested experimentally under static flexural loading, four out of eight were filled with normal concrete (CFST beams). Particularly, the partial CFRP strengthening scheme was used, which wrapped the bottom-half of the beams cross-section (U-shaped wrapping), in order to use the efficiency of high tensile strength of CFRP sheets at the tension stress only of simply supported beams. In general, the results showed that the CFRP sheets significantly improved the ultimate strength and energy absorption capacities of the CFST beams with very limited improvement on the related HST beams. For example, the load and energy absorption capacities for the CFST beams (tube section class 1) were increased about 20% and 32.6%, respectively, when partially strengthened with two CFRP layers, and these improvements had increased more (62% and 38%) for the same CFST beams using tube class 3. However, these capacities recorded no much improvement on the related unfilled HST beams when the same CFRP strengthening scheme was adopted.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7878-7884
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• 2015

Marine sea water pump with impeller using carbon fiber block was developed to prevent the impeller corrosion by the salinity. A numerical analysis was carried out in order to optimize the impeller and volute design for marine sea water pump and to investigate the sensitivity of the related parameters(impeller thickness, surface roughness) using CFD commercial code. The impeller thickness is limited because of the weight. Since the impeller using the carbon fiber lights, the thickness which has a maximum efficiency can be used. The results show that the surface roughness leads to an 7% reduction in pump efficiency.

• Korean Journal of Computational Design and Engineering
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• v.21 no.4
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• pp.389-396
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• 2016

The necessity for environment-friendly material development has emerged in the recent automotive field due to stricter regulations on fuel economy and environmental concerns. Accordingly, the automotive industry is paying attention to carbon fiber reinforced plastic (CFRP) material with high strength and stiffness properties while the lightweight. In this study, we determine a shape of lower control arm (LCA) for maximizing the strength and stiffness by optimizing the thickness of each layer when the stacking angle is fixed due to the CFRP manufacturing problems. Composite materials are laminated in the order of $0^{\circ}$, $90^{\circ}$, $45^{\circ}$, and $-45^{\circ}$ with a symmetrical structure. For the approximate optimal design, we apply a sequential two-point diagonal quadratic approximate optimization (STDQAO) and use a process integrated design optimization (PIDO) code for this purpose. Based on the physical properties calculated within a predetermined range of laminate thickness, we perform the FEM analysis and verify whether it satisfies the load and stiffness conditions or not. These processes are repeated for successive improved objective function. Optimized CFRP LCA has the equivalent stiffness and strength with light weight structure when compared to conventional aluminum design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.245-251
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• 1999

Carbon fibre reinforced plastic(CFRP) plate is one of the alternative materials for strengthening of reinforced and prestressed concrete members due to excellent strength and light weight. In this paper, the behavior of slabs strengthened with CFRP plate is observed and analyzed from the test results. Especially specimens with thick plate is tested when large moment and large shear force appear in same position. The failure mode is a peeling-off of the CFRP plate due to flexural-shear crack. This is observed near the loading points with thick plates. Because of this failure mode, thickness of CFRP plates does not influence on the failure loads. Depending on the loading pattern, it is necessary to consider different design criteria for reinforced concrete members with external reinforcement. When large moment and large shear force appear in same location, maximum thickness may limit to 0.6mm and ratio between moment of strengthened slab and moment of unstrengthened slab is proposed 1.5-2.0.

• Advances in concrete construction
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• v.10 no.4
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• pp.289-299
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• 2020

A reliability analysis of the axial compressive load bearing capacity of postfire reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets was presented. A 3D finite element (FE) model was built for heat transfer analysis using software ABAQUS. Based on the temperature distribution obtained from the FE analysis, the residual axial compressive load bearing capacity of RC columns was worked out using the section method. Formulas for calculating the residual axial compressive load bearing capacity of the columns after fire exposure and the axial compressive load bearing capacity of postfire columns retrofitted with CFRP sheets were developed. Then the Monte Carlo method was used to analyze the reliability of the axial compressive load bearing capacity of the RC columns retrofitted with CFRP sheets using a code developed in MATLAB. The effects of fire exposure time, load ratio, number of CFRP layers, concrete cover thickness, and longitudinal reinforcement ratio on the reliability of the axial compressive load bearing capacity of the columns after fire were investigated. The results show that within 60 minutes of fire exposure time, the reliability index of the RC columns after retrofitting with two layers of CFRPs can meet the requirements of Chinese code GB 50068 (GB 2001) for safety level II. This method is effective and accurate for the reliability analysis of the axial load bearing capacity of postfire reinforced concrete columns retrofitted with CFRP.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.15-21
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• 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.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.667-675
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• 2004

This paper presents the failure mode and strengthening design of reinforced concrete slab strengthened with Carbon Fiber Reinforced Polymer(CFRP) grid. Parameters involved in this experimental study are FRP grid reinforcement quantity, repair mortar thickness, the presence of anchor, and strengthening in compression. In this study, there are different failure types with increasing the CFRP grid strengthening reinforcement. On the low strengthening level, CFRP grid in repair mortar cover ruptures. On the moderate strengthening level, there is a debonding shear failure in the interface of carbon FRP grid because of the excessive shear deformation. On the high strengthening level, diagonal shear failure occurs. With the increasing of FRP grid reinforcement, the strengthening effect increased, but the ductility decreased. By limiting the strengthening level, it can be achieved to prevent shear failure which result in sudden loss in the resisting load capacity. CFRP rupture failure is desirable, because CFRP ruptured concrete slab keeps the same load capacity and ductility haying before strengthening even after failure. Finally, design guideline and procedure are given for strengthening of concrete slab with CFRP grid.

• Journal of the Korean Society of Safety
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• v.28 no.4
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• pp.14-18
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• 2013

Blades of horizontal axis are nowadays made of composite materials. Generally, composite materials satisfy design provides lower weight and good stiffness, while laminate composites have often damages as like the delamination and cracks at the interface of laminates. The box spar and tail parts of a blade are composed of the CFRP/GFRP hybrid laminate composites. However, delamination and the interfacial crack often occur in the interface of CFRP/GFRP hybrid laminate composites under the mixed mode fracture condition, especially mode I and mode II. Therefore, there is a need for the evaluation of the mixed mode fracture behavior during the delamination of CFRP/GFRP hybrid laminates. This study shows the experimental results for the delamination fracture toughness in CFRP/GFRP hybrid laminate composites. Fracture toughness experiments and estimation are performed by using DMMB(Dissimilar mixed mode bending) specimen. The materials used in the test are a commercial woven type CFRP(Carbon fiber reinforced plastic) prepreg(CF3327) and UD type GFRP(Glass fiber reinforced plastic) prepreg(HD224A). A CFRP/GFRP hybrid laminate composite is composed by the 10 plies CFRP and GFRP prepreg for DMMB. A thickness of CFRP and GFRP layer is 2.5mm and 3.0mm, respectively. Also the fulcrum location which is a loading parameter is changed from 80 to 100mm on the specimen of length 120mm because it defines the ratio of mode I to mode II. In this study, the effects of the fulcrum location are evaluated in the viewpoint of energy release rate in mode I and mode II contribution. The results show that the delamination crack initiates at higher displacement and lower load according to the increase of the fulcrum location ratio. And the variation of the energy release rate for mode I and II contributions for the mode mixity are shown.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.2
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• pp.102-108
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• 2010

Recently, carbon fiber reinforced plastic(CFRP) composite materials have been widely used in various fields of engineering because of its advanced properties. Also, CFRP composite materials offer new design flexibilities, corrosion and wear resistance, low thermal conductivity and increased fatigue life. However CFRP composite materials are susceptible to impact damage due to their lack of through-thickness reinforcement and it causes large drops in the load-carrying capacity of a structure. Therefore, the impact damage behavior and subsequently load-carrying capacity of impacted composite materials deserve careful investigation. In this study, the residual strength and impact characteristics of plain-woven CFRP composites with impact damage are investigated under axial tensile test. By using obtained residual strength and Tan-Cheng failure criterion, residual strength of CFRP laminate with arbitrary fiber angle were evaluated.

• Advanced Composite Materials
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• v.16 no.1
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• pp.1-10
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• 2007

Composite materials consisting of crushed carbon fiber reinforced plastics (CFRP) pieces and acrylonitrile-butadiene-styrene (ABS) resin were prepared by an injection mold method to solve the problem of recycling of CFRP. The electrical properties, such as electrical resistivity, alternating current impedance and electromagnetic interference (EMI) shielding effect, were measured for the composites. The electrical resistivity of the composites showed a percolation type of conduction behavior and no difference between parallel and perpendicular to the injection direction was observed for CFRP content higher than the critical value. Measurement of alternating current impedance revealed that the conduction mechanism is attributed to the direct conductive paths generated by distributed carbon fibers; however, strong frequency dependence of the impedance was observed for the CFRP content near the critical one. The frequency dependence of the impedance is caused by the inter-fiber connection and can be expressed as a simple equivalent circuit. The absorption component of shielding effect (SE) was smaller than the expected value estimated from its resistivity. The decline of SE is thought to be caused by the decrease in effective thickness due to fiber orientation.