• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.135-144
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• 2007

Recently, fiber-reinforced plastic(FRP) wraps are blown as an effective material for the enhancement and rehabilitation of aged concrete structures. The purpose of this investigation is to experimentally investigate behavior of concrete cylinder wrapped with FRP materials. Experimental parameters include compressive strength of concrete cylinder, FRP material, and confinement ratio. This paper presents the results of experimental studies on the performance of concrete cylinder specimens externally wrapped with aramid, carbon and glass fiber reinforced Polymer sheets. Test specimens were loaded in uniaxial compression. Axial load, axial and lateral strains were investigated to evaluate the stress-strain behavior, ultimate strength ultimate strain etc. Test results showed that the concrete strength and confinement ratio, defined as the ratio of transverse confinement stress and transverse strain were the most influential factors affecting the stress-strain behavior of confined concrete. More FRP layers showed the better confinement by increasing the compressive strength of test cylinders. In case of test cylinders with higher compressive strength, FRP wraps increased the compressive strength but decreased the compressive sham of concrete test cylinders, that resulted in prominent brittle failure mode. The failure of confined concrete was induced by the rupture of FRP material at the stain, being much smaller than the ultimate strain of FRP material.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.57-62
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• 1997

The combined structure of hybrid composite made through the bonding process of materials of different properties greatly defines its mechanical characteristics, as the results of the experiments on materials of different properties show much dissimilarity. When carbon/epoxy materials are applied to hybrid composite, the carbon materials helps to improve the mechanical properties of the hybrid composite, and the epoxy reduces its fracture strain and impact resistance. Carbon fiber which is now in general commercialization is classified as high modulus or high strength system, and its manufacturing methods are various. The study of the materials having combined structure is focused on the numerical analysis of the layers of bonding surface in materials with difference modulus. The hybrid composite made through the multilayered bonding of reinforced aluminium sheets with aramid fiber now faces the marketing phase, and especially its excellent fatigue resistance and mechanical properties promote active researches on the similar products of hybrid composite. This study aims to investigate the effects of CFRP volume ratio and fiber's orientation over the properties of mechanical strength and fatigue life of the hybrid composite, AI7075/CFRP. To carry out this study, static tensile and fatigue tests were given to some of the panels which, made through the co-cure processing in an autoclave, have different CFRP volume ratio and carbon fiber orientations.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.231-237
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• 2000

A15052/AFRP laminates were developed principally to obtain a material with good fatigue strength, in which possible cracks would grow very slowly. Weight savings of more than 30% should be attainable in practice. Also, the crack bridging fibers could still was carry a significant part of the load over the crack, thus the COD and stress intensity factor was reduced at the crack tip. A15052/ AFRP laminates consists of three thin sheets of 5052-H34 aluminum alloy and two layers of [0] unidirectional aramid fiber prepreg. The cyclic-bending moment test was investigated based on applying the five kinds of bending moments. The size of the delamination zone produced between 5052-H34 aluminum alloy sheets and fiber-adhesive layers was measured from ultrasonic C-scan pictures taken around the fatigue crack. In addition, the relationship between the cyclic-bending moment and the delamination zone size was studied and the effect of fiber bridging mechanism was also considered.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.8
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• pp.149-154
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• 1999

FRMLs(Fiber Reinforced Metal Laminates) is a new type of hybrid materials. FRMLs consists of high strength metal and fiber which are laminated using a structural adhesive bond(epoxy resin). The effect of resin mixture ratios on the fatigue crack propagation behavior and mechanical property of Aramid fiber reinforced aluminum composites was investigated. The epoxy, diglycidylether of bisphenol A(DGEBA) was cured with methylene dianiline(MDA) with or without accelerator(K-54). Eight kinds of resin mixture ratio were tested for the experiment ; five kinds of FRMLs(1))epoxy & curing agent) and three kinds of FRMLs(2)(epoxy & curing agent & accelerator). FRMLs(2) have a more effective characteristics on the fatigue crack propagation behavior and mechanical property than FRMLs(1)

• Composites Research
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• v.13 no.3
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• pp.21-29
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• 2000

The optimum design of hybrid laminated composites for iso-strain structure has been studied by controling fiber orientations and thicknesses of each layer. Fiber orientations and thicknesses of each layer for iso-strain structure were designed. Combining the laminates of each layer of different reinforcing material, the constitutions of hybrid laminated composite for iso-strain structure were obtained. All these calculations were formed on computer systems, automatically for the hybridization. Using the data of some specific laminated composite such as glass and aramid reinforced composites, the constitutions of hybrid laminated composites for iso-strains structure were designed and verified by lamination theory. The strains of each layer of hybrid laminated composites are calculated and they turned out to be good agreements with the results obtained lamination theory.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.501-507
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• 1996

The final objectives of this study are to present the theoretical formula for reasonable structural analysis and practical codes on the repair/strengthening of damaged reinforced concrete structrues. For that purpose, in last year, preliminary experiments for flexure and shear of beam structure using carbon sheet and steel plate were performed, and in sequence, in this year, using aramid fiber sheet and steel plate more extensive experiment were performed. Repair for the performance of flexure and shear was focused on, and main variables were selected considering aplicablilty for practical field, such as, spacing of anchor bolt, lapping, jacking up, preloading level, and fiber difection as well as length of repairing plate and thickness. so new results from various angles are to be presented.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.598-604
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• 1997

In recent years, strengthening by epoxy-bonded steel plates, carbon fiber sheets, aramid fiber sheets and so on, is spotlighted. Among them, the method using steel plates is most widely applied. Most studies have dealt with strengthening by epoxy-bonded steel plates. However the actual behavior of strengthened RC beams are not well established. Particularly, the studies on the separation load thar affects failure load of the beam are relatively insufficient. In this study, test parameters are the magnitude of pre-load, plate length, plate thickness, existence and spacing of anchor bolt, the number of plate layer and the height of side strengthening, 17reinforced concrete beams are strengthened by steel plates according to test parameters. Deflection, failure load, strains of reinforcing bar, concrete and plate are measured from tests(4 points loading). The failure mode, and separation load are analyzed from these measured data. The difference between Robert's theory and test results is discussed, and the prediction equation for separation load in the case of rip off is proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.6
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• pp.154-163
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• 2006

This paper presents a nonlinear analysis method for the reinforced concrete beams strengthened by the external bonding of high strength, lightweight fiber sheets on the tension face of the beams. The method is based on the results of experimental studies. The experimental study involved tensile tests of 120 specimens to evaluate the tensile properties of fiber sheets(carbon, glass, and aramid fiber) and bending tests of 75 beams strengthened with various types of fiber sheets to evaluate the flexural capacities. Based on these experimental results, reasonable rupture strains of the fiber sheets were estimated. The nonlinear flexural analysis considered nonlinear flexural stresses as compressive and tensile stresses of concrete, load-deflection curves, and rupture strains of fiber sheets. The nonlinear flexural analysis accurately predicts the load-deflection response and the flexural behavior of the retrofitted beams.

• Korean Journal of Materials Research
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• v.6 no.8
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• pp.786-795
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• 1996

The fiber reinforced thermoplastics(FRTP) were prepared with polypropylene fiber(PP) as matrix and polyvinyl alchol(VF), aramid(KF) or polyamide fiber(PAF) as the reinforcing materials using the integrated fiber mixing apparatus. The reinforced thermoplastic sheets were prepared by com¬pression molding and their morphology, rheological and mechanical properties were characterized. In the morphological properties of composites, the wettability of the reinforced thermoplastics were decreased in proportion to the content of fibers. At low angular frequency, the viscosity of PAF /PP and VF/PP composite was increased with the content of reinforced fiber. However at high frequency the viscosity of composite reinforced with 5~20wt% fiber, was shown the reduced values which approaches that of the neat matrix. The mechanical properties of the composite were changed with the content of reinforecd fiber, and VF/PP and KF/PP composite had better properties than PAF/PP system.

• Journal of Adhesion and Interface
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• v.22 no.4
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• pp.118-127
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• 2021

In this study, the mechanical properties of vulcanized rubber were evaluated through compounding by controlling filler content to improve the mechanical properties of NBR rubber. Aramid and glass fibers with excellent heat resistance were used as fillers, and ceramics were additionally used in anticipation of a complementary effect, and as for the ceramic materials, needle-shaped and plate-shaped ceramics were used. Each filler was used in an amount of 5.0, 10.0, 15.0, and 20.0 phr in order to investigate the basic properties according to the amount of filler. To confirm the complementary effect through ceramic application, each 10.0 phr fiber and ceramic were mixed with 1:1 ratio to evaluate mechanical properties. As a result, it was confirmed that the decreasing ratio of tensile strength after heat aging was small in the order of aramid fiber, acicular ceramic, glass fiber, and plate ceramic in the case of applying the filler alone. In addition, the mechanical characteristics of vulcanized rubber using composite filler based on fibers and ceramics were evaluated, and it was confirmed that the composite filler had a complementary effect on thermal aging.