• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.2
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• pp.89-96
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• 2018

Purpose: The aim of this study was to evaluate the effect of delayed time, surface treatment, and repair materials on repair of bis-acryl composite resin through comparison of shear bond strength and to evaluate the utility of bis-acryl composite resin repair using polymethyl methacrylate resin. Materials and Methods: A total of 90 bis-acryl composite resin specimens were fabricated and classified into 9 test groups, each of 10 pieces according to delayed time, surface treatment and repair material. The shear bond strength of each specimen was measured using a universal testing machine immediately after fabrication and analyzed using a statistical analysis program (IBM SPSS statistics 20). After the shear bond strength measurement, the fracture surface of the specimen was observed. Results: The highest shear bond strength ($17.54{\pm}3.14MPa$) was observed in the experimental group bonded immediately with a light-curing flowable composite resin using a bonding agent. Conclusion: When repairing bis-acryl composite resin, it is necessary to consider whether to remake according to the delayed time. For effective repair, it is desirable to consider appropriate materials and surface treatment methods according to the site or purpose of use.

• Composites Research
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• v.31 no.1
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• pp.1-7
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• 2018

In the case of a conventional composite patch repair using a heat blanket, the adhesive is pressurized using only a vacuum bag. In this study, however, a pressurization system has been developed to apply additional air pressure on the vacuum bag. In order to verify the performance of the developed system, the composite laminates were repaired with scarf patches and then tested under tensile load to be compared with the strength of the defect-free laminate. Tensile tests were also conducted on specimens with the same configuration but bonded in an autoclave. As a result of the test, the tensile strengths of the specimens repaired using the heat blanket with vacuum only without external pressure, the specimens repaired with additional pressure by the developed system, and the specimens repaired with the same external pressure in an autoclave, showed the strength recovery ratios of 74.9, 81.0, and 78.2%, respectively. The results of the tensile test after moisture saturation and the dried fatigue test also showed that the strength recovery ratios of the specimens repaired under the external pressure of 1 atm using the developed system are slightly higher than that of specimens bonded in autoclave.

• Structural Engineering and Mechanics
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• v.55 no.3
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• pp.511-523
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• 2015

Damaged steel-concrete composite girders can be repaired and retrofitted by epoxy-bonded carbon fiber-reinforced polymer (CFRP) sheets to the critical areas of tension flanges. This paper presents the results of a study on the behavior of damaged steel-concrete composite girders repaired with CFRP sheets under static loading. A total of seven composite girders made of I20A steel sections and 80mm-thick by 900mm-wide concrete slabs were prepared and tested. CFRP sheets and prestressed CFRP sheets were used to repair the specimens. The specimens lost the cross-sectional area of their tension flanges with 30%, 50% and 100%. The results showed that CFRP sheets had no significant effect on the yield loads of strengthened composite girders, but had significant effect on the ultimate loads. The yield loads, elastic stiffness, and ultimate bearing capacities of strengthened composite girders had been changed as a result of prestressed CFRP sheets, the utilization ratio of CFRP sheets could be effectively improved by applying prestress to CFRP sheets. Both the yield loads and ultimate bearing capacities had been changed as a result of steel beam's flange damage level and CFRP sheets could cover the girders' shortage of bearing capacity with 30% and 50% flange damage, respectively.

• Journal of the Society of Disaster Information
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• v.12 no.1
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• pp.54-61
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• 2016

The use of advanced composite materials in strengthening and repair of existing structures is increasing rapidly. This paper describes an effectiveness of a bonding of carbon fiber reinforced sheets to corroded steel members for the repair. Three types of surface treatment, what we call cleaning, of corroded plate are chosen as parameters. They are "without cleaning","removal of painting by brushing" and "complete removal of painting". From the experimental study, the following findings are obtained. 1) When the steel plate is subjected to tensile force, carbon fiber sheets adhered to the painted steel gives a higher strength against peeling compared to that of the plate without painting, 2) The grade of surface treatment, or cleaning of the corroded steel plate affects the strengthening effect.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.491-496
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• 2001

In recent years, the research and development about the new material proceed rapidly and actively in the building industry. As building structures become bigger, higher and more specialized, so does the demand for material with higher strength. In the future, we will need to research repair and rehabilitation to make high strength concrete mixed steel fibrous building safe. The carbon fiber reinforced plastic bonding method is widely used in reinforcing the existing concrete structure among the various methods. The repair of initiate loaded reinforced high-strength concrete beams mixed steel fibrous with epoxy bonded Carbon Fiber Sheets(CFS) was investigated experimentally. The CFS thickness and length were varied to assess the peel failure at the curtailment of CFS, The behaviour of the repaired beams was represented by load-longitudinal steel strain relation and failure modes were discussed. The test results indicate that CFS is very effective for strengthening the demand beams and controlling deflections of reinforced high strength concrete beams mixed steel fibrous happen diagonal crack, the increase in the number of CFS layers over two layers didn't effect the increase in the strength of beams.

• Structural Engineering and Mechanics
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• v.26 no.4
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• pp.427-439
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• 2007

The exploitation of fibre reinforced polymer composites, as external reinforcement is an evergreen and well-known technique for improving the structural performance of reinforced concrete structures. The demand to use FRP composites in the civil engineering industry is mainly due to its high strength, light weight, and stiffness. This paper exemplifies the shear strength of partially precracked reinforced concrete rectangular beams repaired with externally bonded Bi-Directional Carbon Fibre Reinforced Polymer (CFRP) Fabrics strips. All specimens were cast in the laboratory environment without any internal shear reinforcement. The test parameters were longitudinal tensile reinforcement, shear span to effective depth ratio, spacing of CFRP strips, and orientation of CFRP reinforcement. It mainly focuses on the shear capacity and modes of failure of the CFRP strengthened shear beams. Results have shown that the CFRP repaired beams attained a shear enhancement of 32% and 107.64% greater than the control beams. This study underscores that the CFRP strip technique significantly enhanced the shear capacity of precracked reinforced concrete rectangular beams without any internal shear reinforcement.

• Structural Engineering and Mechanics
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• v.84 no.6
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• pp.799-811
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• 2022

Adhesive bonding has seen rapid development in recent years, with emphasis to composite patch repairing processes of geometric defects in aeronautical structures. However, its use is still limited given its low resistance to climatic conditions and requirement of specialized labor to avoid fabrication induced defects, such as air bubbles, cracks, and cavities. This work aims to numerically analyze, by the finite element method, the failure behavior of a damaged plate, in the form of a bonding defect, and repaired by an adhesively bonded composite patch. The position and size of the defect were studied. The results of the numerical analysis clearly showed that the position of the defect in the adhesive layer has a large effect on the value of J-Integral. The reduction in the value of J-Integral is also related to the composite stacking sequence which, according to the mechanical properties of the ply, provides better load transfer from the plate to the repair piece through the adhesive. In addition, the increase in the applied load significantly affects the value of the J-Integral at the crack tip in the presence of a bonding defect, even for small dimensions, by reducing the load transfer.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.4
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• pp.419-430
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• 2007

Purpose: This in vitro study evaluated shear bond strengths of surface treatment porcelains with four porcelain repair systems simulating intraoral bonding of composite resin to feldspathic porcelain or pressable porcelain. Material and methods: Eighty Porcelain disks were prepared. Group A: forty disk specimens were fabricated with Feldspathic Porcelain($Omega^{(R)}900$, Vident, Menlo Park, CA, USA). Group B: forty disk specimens were fabricated with Pressable Porcelain(IPS Empress 2 ingot, Ivoclar-Vivadent, Schaan, Liechtenstein, Germany). Each groups was divided into 4 subgroups and composite resin cylinders were bonded to specimen with one of the following four systems: Clearfil Porcelain Bond(L. Morita, Tustin, CA, USA), Ulradent Porcelain Etch. (Ultradent, Salt Lake City UT, USA), Porcelain Liner-M(Sun Medical Co., Kyoto, Japan), Cimara Kit(Voco, Germany). After surface conditioning with one of the four porcelain repair systems substrate surfaces of the specimen were examined microscopically(SEM). Shear bond strengths of specimens for each subgroup were determined with a universal testing machine (5mm/min crosshead speed) after storing them in distilled water at $37{\pm}1^{\circ}C$ for 24 hours. Stress at failure was measured in $MP_a$, and mode of failure was recorded. Differences among four repair systems were analyzed with two way ANOVA and Duncan test at the 95% significance level. Results: In the scanning electron photomicrograph of the treated porcelain surface, hydrofluoric acid etched group appeared the highest roughness. The shear bond strength of the phosphoric acid etched group was not significantly(p>0.05) different between feldspathic porcelain and pressable porcelain. But in no treatment and roughened with a bur group, the shear bond strength of the feldspathic porcelain was significantly higher than that of the pressable porcelain. In hydrofluoric acid etched group, the shear bond strength of the pressable porcelain was significantly higher(p<0.05). Conclusion: 1. Treatment groups showed significantly greater shear bond strengths than no treatment group(p<0.05). 2. Group with more roughened porcelain surface did not always show higher shear bond strengths. 3. In phosphoric acid etched group, there was no significant difference in shear bond strength between feldspathic porcelain and pressable porcelain(p>0.05). However in the other groups, there were significant differences in shear bond strengths between feldspathic porcelain and pressable porcelain(p<0.05).

• Steel and Composite Structures
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• v.14 no.1
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• pp.41-55
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• 2013

Fiber reinforced polymers (FRP) materials are increasingly being used for strengthening and repair of steel structures. An issue that concerns engineers in steel members which are retrofitted with FRP is stress experienced due to temperature changes. The changing temperature affects the interface bond between the FRP and Steel. This research focused on the effects of cyclical thermal loadings on the interface properties of FRP bounded to steel members. Over fifty tests were conducted to investigate the thermal effects on bonding between FRP and steel, which were cycled from temperature of $-11^{\circ}C$ ($12^{\circ}F$) to $60^{\circ}C$ ($140^{\circ}F$) for 21-36 days. This investigation consisted of two test protocols, 1) the tensile test of epoxy resin, tack coat, FRP and FRP-steel plate, 2) tensile test of each FRP compound and FRP with steel after going through thermal cyclic loading. This investigation reveals an extensive reduction in the composite's strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.965-970
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• 2002

The strengthening of concrete structures in situ with externally bonded carbon fiber is increasingly being used for repair and rehabilitation of existing structures. Carbon fiber is attractive for this application due to its good tensile strength, resistances to corrosion, and low weight. Generally bond strength and behavior between concrete and carbon fiber mesh(CFM) is very important, because of the enhanced bond of CFM. Therefore if bond strength is sufficient, it will be expected to enhance reinforcement effect. If insufficient, reinforcement effect can not be enhanced because of bond failure between concrete and CFM. This study is to investigate the bond strength of CFM to the concrete using direct pull-out test and tensile-shear test. The key variables of the experiment are the location of clip, number of clips and thickness of cover mortar. The general results indicate that the clip anchorage technique for increasing bond strength with CFM appear to be effective to maintain the good post-failure behavior.