• Composites Research
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• v.31 no.6
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• pp.332-339
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• 2018

Fiber metal hybrid laminate (FML) can be used as an economic material with superior mechanical properties and light weight than conventional metal by bonding of metal and FRP. However, there are disadvantages that it is difficult to predict fracture behavior because of the large difference in properties depending on the type of fiber and lamination conditions. In this paper, we study the failure behavior of hybrid materials with laminated glass fiber reinforced plastics (GFRP, GEP118, woven type) in Al6061-T6 alloy. The Al alloys were coated with GFRP 1, 3, and 5 layers, and fracture behavior was analyzed by using a static test and a low cycle fatigue test. In the low cycle fatigue test, strain - life analysis and the total strain energy density method were used to analyze and predict the fatigue life. The Al alloy did not have tensile properties strengthening effect due to the GFRP coating. The fatigue hysteresis geometry followed the behavior of the Al alloy, the base material, regardless of the GFRP coating and number of coatings. As a result of the low cycle fatigue test, the fatigue strength was increased by the coating of GFRP, but it did not increase proportionally with the number of GFRP layers.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1952-1959
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• 1999

The work factor approach, so-called single specimen technique could be used to determine energy release rate from a single test record for unidirectional CLS specimen. In the present study, the work factor approach was extended to determine the mixed-mode fracture toughness of multi-directional graphite/epoxy laminated composites. Multi-directional CLS specimens were used for fracture tests. The stacking sequences used for the lap and the strap were $[90_2/0_2]_s/[0_4/90_4]_s$ and $[0/\pm45/0]_s/[0_2/\pm45_2/0_2]_2$, respectively. For both cases, the fracture toughness determined from the work factor approach was compared with that determined from the compliance method. It was found that both methods produced fracture toughness within a maximum 15% difference for each stacking sequence. The fractography analysis also showed that the fiber bridging occurred for$[0/\pm45/0]_s/[0_2/\pm45_2/0_2]_2$ case while it did not occur for $[90_2/0_2]_s/[0_4/90_4]_s$ case.

• Composites Research
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• v.15 no.1
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• pp.53-60
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• 2002

Composite ablative tubes required capabilities of ablative and structural characteristics were fabricated through filament winding technique and several experiments were conducted to evaluate the structural performance of composite ablative tubes. For this purpose, manufacturing procedures were briefly described and then resin digestion method was applied to measure the fiber volume fraction and the void content of composite ablative tubes. The configuration of tensile specimen fur composite ablative tubes with not losing the continuity of reinforced fibers was suggested by evaluating mechanical properties of several types of the specimen with different widths. Also, suitable processing variables for composite ablative tubes were determined by evaluating mechanical properties of several types of the specimen with different processing variables. In addition, acoustic emission signals were obtained during the proof test and could be applicable to study the crack initiation and the damage mode of composite ablative tubes. Finally, the structural reliability of composite ablative tubes could be verified to satisfy design requirements through the proof and burst tests.

• Polymer(Korea)
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• v.33 no.6
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• pp.530-536
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• 2009

A cycloaliphatic epoxy/acidic anhydride system incorporating short carbon fibers (SCF) and short glass fibers (SGF) was fabricated and thermal/mechanical properties were characterized. At low filler content both SCF- and SGF-reinforced composites showed a similar decrease in coefficient of thermal expansion (CTE), measured by a thermomechanical analyzer, with increasing loadings, above which SCF became more effective than SGF at reducing the CTE. Experimental CTE data for the SCF-reinforced composites is best described by the rule of mixtures at lower SCF contents and by the Craft-Christensen model at higher SCF contents. Storage modulus (E') at $30^{\circ}C$ and $180^{\circ}C$ was greatly enhanced for short fiber-filled composites compared to unfilled specimens, Scanning electron microscopy of the fracture surfaces indicated that the decreased CTE and the increased E' of the short fiber-reinforced composites resulted from good interfacial adhesion between the fibers and epoxy matrix.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.11
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• pp.2771-2776
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• 2000

In this work, the effect of surface treatment of prepreg on the mode I fracture behavior was studied. Unidirectional (0-deg) double cantilever beam (DCB) specimens were used for fracture tests. Two groups of DCB specimens were made: the first group was made of prepregs surface-treated by Ar(sup)+ ion beam under oxygen environment and the second group was made of regular prepregs. For both groups, fracture resistance curve (R-curve) was determined and compared to each other, Results showed that resistance behavior of the first group is better than that of the second group. That is, mode I fracture toughness, G(sub)Ic of the first group is 24% larger than that of the second group. SEM examination shows that the improvement of G(sub)Ic is due to the increase of interfacial strength between plies.

• Composites Research
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• v.23 no.4
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• pp.44-51
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• 2010

Recently, to solve the problems associated with the neutralization and corrosion of reinforced concrete compression members, the structural configurations such as CFFT (Concrete Filled GFRP Tube) and RCFFT (Reinforced Concrete Filled GFRR Tube) have been developed and applied to main members of civil engineering structure. These members can increase structural performance in terms of structural stability, ductility as well as chemical resistance compared with conventional concrete structural members. Many researches in numerous institutions to predict the load carrying capacity of the concrete compression member strengthened with FRP materials have been conducted and they have been suggested an equation for the prediction of the load carrying capacity of the members. Through the review of the research results, it was found that their results are similar each other. Moreover, it was also found that the results are not directly applicable to our specimens since the results are largely depended upon the member configurations. Also, since the accurate design criteria for the RC members strengthened with FRP such as RCFFT have not been established properly, relevant theoretical and experimental investigations must be conducted for the application to the practical structures. In this study, structural behavior of RCFFT was evaluated through compressive and quasi-static flexural tests in order to formulate design criteria for the structural design. In addition, the RCFFT members were also investigated to examine their confinement effect and the equations capable of estimating the compressive ultimate strength and flexural stiffness of the RCFFT members were proposed.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.67-70
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• 2005

The carbon fiber reinforced/epoxy laminated composites were fabricated with initial fiber failures within the unidirectional fiber pre-pregnated ply. The fiber failures were made intentionally either parallel to and/or perpendicular to the unidirectional fibers within the ply. The pre-made clear-cut cracks were found to be healed partially after laminating process. The laminates were impacted with or without initial fiber failures within the laminates. The force versus deflection curves were compared. The partially healed laminates showed the reduced laminate stiffness as compared to those without any intentional fiber failures. The impact curves were compared with size and the location of the initial failures varied.

• Composites Research
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• v.31 no.6
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• pp.299-303
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• 2018

In order to improve the interfacial bonding force and reaction polymerization degree of the carbon fiber reinforced nylon 6 composite material, the surface of the existing epoxy-sizing carbon fiber was desized to remove the epoxy and treated with urethane, nylon and phenoxy sizing agent, was observed. The interfacial bond strength of the resized carbon fiber was confirmed by IFSS (Interfacial Shear Strength) and the fracture surface was observed by scanning electron microscope. The results showed that the interfacial bonding strength of the carbon fiber treated with nylon and phenoxy sizing agents was higher than that of urethane - based sizing. It has been found that the urethane - type resizing carbon fiber has lower interfacial bonding strength than the conventional epoxy - sizing carbon fiber. This result shows that the interfacial bonding between carbon fiber and nylon 6 is improved by removing low activity and smoothness of existing carbon fiber.

• Elastomers and Composites
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• v.48 no.2
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• pp.133-140
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• 2013

Carbon fiber reinforced polymer (CFRP) composites consist of carbon fibers in a polymer matrix. Recently, CFRP composites having high thermal stability and low outgassing are finding their use in high performance materials for aerospace and electronics applications under high temperature and high vacuum conditions. Cyanate ester resin is one of the most suitable matrix resins for this purpose. In this study, proper combination of cyanate ester and catalyst, curing behavior, and cure cycle were determined by chemorheology. Optimum condition was found to be catalyst content of 100 ppm and curing temperature of $150^{\circ}C$. Thermal stability and outgassing of cured resin composition were analyzed and the results showed thermal decomposition temperature of $385^{\circ}C$ and total mass loss of 0.29%. The CFRP prepregs and subsequent composites were fabricated by predetermined resin composition and the cure condition. Tensile moduli of the composites were compared with theoretical models and the results were very consistent.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.920-925
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• 2012

A study of vehicle weight lightening has been progressed to reduce the fuel consumption. In this paper, the body floor in an EV (Electric Vehicle) bus has been applied by composites as CFRP and GFRP. In order to analyse a various reliability and safety, an experiment and FEM analysis was carried out to obtain weight lightening. Especially, the joint. An effective design is obtained through an experiment as well as FEM analysis. Results of stress analysis of GFRP material showed twice as much displacement than those of CFRP material. Among three kinds of joint methods, the bond joint method is occurred to a substantial shape change in the body and floor. It is found that the rivet joints are fairly suitable for stress sustaining capability.