• Composites Research
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• v.29 no.3
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• pp.111-116
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• 2016

The tilting pad journal bearing for the turbo compressor application has a role to support high speed and heavy loading rotor. White metal has been widely used for the bearing material but the conventional bearing is immediately suspended and induces serious serious damage to the rotor under the unexpected oil cut situation or the insufficient oil film formation. The carbon fiber reinforced composite having high specific stiffness, specific strength and excellent tribological characteristics can solve these seizure problems. In this work, the study on the durability of high thermal resistance carbon fiber/epoxy composite tilting pad journal bearing under oil cut situation was conducted. The material properties of the composite materials including tensile, compressive and interlaminar properties were measured at room and high temperature of oil cut situation. To investigate the possibility of failure of composite tilting pad journal bearing under oil cut situation, the stress distribution of the composite bearing was analyzed via finite element analysis and the Tsai-Wu Failure index was calculated. To verify the failure analysis results, the oil cut tests for the composite tilting pad journal bearing were conducted using industrial test bench.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.894-900
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• 1998

An interphase between carbon fiber and epoxy matrix was introduced to increase impact strength of carbon fiber reinforced composites (CFRC) without sacrificing the interlaminar shear strength. Flexible polymers, I. e., MVEMA (poly(methyl vinyl ether-co-maleic anhydride)) and EMA(poly(ethylene-co-maleic anhydride)), which have reactive functional groups were considered as interphase materials. Weight hain of MVEMA and EMA onto the surface of carbon fibers was evaluated by changing the parameters of electrodeposition process. Electrodeposition mechanism of polymers which have anhydride functional group was identified by IR spectroscopy, that is, the generation of $RCOO^-$ functional group by the attack of hydroxide anion in the basic solution was observed. The weight gain was increased by increasing concentration of polymers, current density, and electrodeposition time. However the excess generation of oxygen gas decreased the weight gain by removing the deposited polymers. Washing in the running water easily removed the deposited polymers which are on the fiber surface without bonding, as a results, only 0.5 wt% of deposited polymers are remained.

• Journal of Korean Society of Steel Construction
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• v.25 no.6
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• pp.601-612
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• 2013

In the present study, details of the TSC beam-to-PSRC column connection for low and middle seismic zones were developed. For ease construction, the top and bottom flanges of the steel section of the TSC beam were discontinuous at the joint face on purpose, while the web passes through the joint. Thus, tensile resistance of the top and bottom flanges is not considered in the calculation of nominal strength of the connection. Cyclic loading tests on two interior connections and an exterior connection were performed to verify the seismic performance. The test parameter for two interior connections was the depth of the TSC beams: 600 and 700 mm including the slab depth. The test results showed that the nominal strength of the connections predicted by KBC 2009 correlated well with the test results. The connection specimens exhibited relatively good deformation and energy dissipation capacities, greater than the requirements for the ordinary and intermediate moment frames. Ultimately, the connection specimens were failed at the story drift ratios of 3.0 to 4.0 % due to local buckling and tensile fracture of the web of the TSC beam passing through the joint. By modifying the existing provisions of ASCE, the joint shear strength of the TSC beam-PSRC column connection was evaluated.

• Journal of Korean Society of Steel Construction
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• v.22 no.2
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• pp.129-137
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• 2010

In this study, a five-story steel frame was designed in accordance with KBC2005 to evaluate the effect of the beam-column connection on the structural behavior. The connections were designed as a fully rigid connection and as a semirigid connection. A fiber model was utilized to describe the moment-curvature relationship of the steel beam and column, and a three-parameter power model was adopted for the moment-rotation angle of the semirigid connection. To evaluate the effects of higher modes on structural behavior, the structure was subjected to a KBC2005-equivalent lateral load and lateral loads considering higher modes. The structure was idealized as a separate 2D frame and as a connected 2D frame. The pushover analysis of 2D frames for the lateral load yielded the top displacement-base shear force, design coefficients such as overstrength factor, ductility ratio, and response modification coefficient, demanded ductility ratio for the semirigid connection,and distribution of plastic hinges. The sample structure showed a greater response modification coefficient than KBC2005, the higher modes were found to have few effects on the coefficient, and the lateral load of KBC2005 was found to be conservative. The TSD connection was estimated to secure economy and safety in the sample structure.

• Polymer(Korea)
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• v.36 no.5
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• pp.612-616
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• 2012

In this work, the effect of chemical treatments of multi-walled carbon nanotubes (MWNTs) on the mechanical interfacial properties of carbon fiber fabric-reinforced composites was investigated. The surface properties of the MWNTs were determined by acid and base values, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. The mechanical interfacial properties of the composites were assessed by interlaminar shear stress (ILSS) and critical stress intensity factor ($K_{IC}$). The chemical treatments based on acid and base reactions led to a significant change of surface characteristics of the MWNTs, especially A-MWNTs/carbon fibers/epoxy composites had higher mechanical properties than those of B-MWNTs and non-treated MWNTs/carbon fibers/epoxy composites. These results were probably due to the improvement of interfacial bonding strength, resulting from the acid-base interaction and hydrogen bonding between the epoxy resins and the MWNT fillers.

• Polymer(Korea)
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• v.37 no.1
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• pp.61-65
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• 2013

In this work, the anodic oxidation of carbon fibers was carried out to enhance the mechanical interfacial properties of carbon fibers-reinforced epoxy matrix composites. The surface characteristics of the carbon fibers were studied by FTIR, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Also, the mechanical interfacial properties of the composites were studied with interlaminar shear strength (ILSS), critical stress intensity factor ($K_{IC}$), and critical strain energy release rate ($G_{IC}$). The anodic oxidation led to a significant change in the surface characteristics of the carbon fibers. The anodic oxidation of carbon fiber improved the mechanical interfacial properties, such as ILSS, $K_{IC}$, and $G_{IC}$ of the composites. The mechanical interfacial properties of the composites anodized at 20% sulfuric/nitric (3/1) were the highest values among the anodized carbon fibers. These results were attributed to the increase of the degree of adhesion at interfaces between the carbon fibers and the matrix resins in the composite systems.

• Restorative Dentistry and Endodontics
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• v.33 no.4
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• pp.405-412
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• 2008

This study was aimed to investigate whether an oxygen inhibition layer (OIL) is essential for the interfacial bonding between resin composite layers or not. A composite (Z-250, 3M ESPE) was filled in two layers using two aluminum plate molds with a hole of 3.7 mm diameter. The surface of first layer of cured composite was prepared by one of five methods as followings, thereafter second layer of composite was filled and cured: Group 1 - OIL is allowed to remain on the surface of cured composite; Group 2 - OIL was removed by rubbing with acetone-soaked cotton; Group 3 - formation of the OIL was inhibited using a Mylar strip; Group 4 - OIL was covered with glycerin and light-cured; Group 5 (control) - composite was bulk-filled in a layer. The interfacial shear bond strength between two layers was tested and the fracture modes were observed. To investigate the propagation of polymerization reaction from active area having a photo-initiator to inactive area without the initiator, a flowable composite (Aelite Flow) or an adhesive resin (Adhesive of ScotchBond Multipurpose) was placed over an experimental composite (Exp_Com) which does not include a photoinitiator and light-cured. After sectioning the specimen, the cured thickness of the Exp_Com was measured. The bond strength of group 2, 3 and 4 did not show statistically significant difference with group 1. Groups 3 and 4 were not statistically significant different with control group 5. The cured thicknesses of Exp_Com under the flowable resin and adhesive resin were 20.95 (0.90) urn and 42.13 (2.09), respectively.

• Composites Research
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• v.30 no.3
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• pp.175-180
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• 2017

Currently, since carbon fiber reinforced plastics (CFRPs) are lightweight and have excellent physical properties, their demand has increased dramatically. Many works have studied the CFRPs based on recycled thermoplastics. In this study, the applicability of recycled composite was evaluated using recycled polyethylene terephthalate (PET). PET was collected from waste materials used in beverage bottles and processed to produce PET films. Optimal thermoforming temperature and time were analyzed by comparing the mechanical properties with forming temperature and time difference for producing PET films. CF mat and PET film were used to determine the suitable parameters for the optimum thermoforming of CF/PET composites. The mechanical properties of each thermoforming condition were verified by bending test. The degree of impregnation of the PET film into the CF mat was evaluated by cross-sectional photographs, whereas the interfacial properties were evaluated by interlaminar shear strength (ILSS). Ultimately, it was confirmed that the thermoforming condition for forming the CF/recycled PET composites yielding the optimal mechanical and interfacial properties was at $270^{\circ}C$ for 5 minutes.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.313-319
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• 2012

In this work, the electroplating of copper was introduced on PAN-based carbon fibers for the enhancement of mechanical interfacial strength of carbon fibers-reinforced composites. The surface properties of carbon fibers were determined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and contact angle measurements. Its mechanical interfacial properties of the composites were studied by interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). From the results, it was found that the mechanical interfacial properties of Cu-plated carbon fibers-reinforced composites (Cu-CFRPs) enhanced with increasing the Cu plating time, Cu content and COOH group up to Cu-CFRP-30. However, the mechanical interfacial properties of the Cu-CFRPs decreased dramatically in the excessively Cu-plated CFRPs sample. In conclusion, the presence of Cu particles on carbon fiber surfaces can be a key factor to determine the mechanical interfacial properties of the Cu-CFRPs, but the excessive Cu content can lead the failure due to the interfacial separation between fibers and matrices in this system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.73-80
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• 2022

In this study, details of NRC beam-column connections were developed in which beam and columns pre-assembled in factories using steel angles were bolted on site. The developed joint details are NRC-J type and NRC-JD type. NRC-J type is a method of tensile joining with TS bolts to the side and lower surfaces of the side plate of the NRC column and the end plate of the NRC beam. NRC-JD type has a rigid joint with high-strength bolts between the NRC beam and the side of the NRC column for shear, and with lap splices of reinforcing bar penetrating the joint and the beam main reinforcement for bending. For the seismic performance evaluation of the joint, three specimens were tested: an NRC-J specimen and NRC-JD specimen with NRC beam-column joint details, and an RC-J specimen with RC beam-column joint detail. As a result of the repeated lateral load test, the final failure mode of all specimens was the bending fracture of the beam at the beam-column interface. Compared to the RC-J specimen, the maximum strength of the specimen by the positive force was 10.1% and 29.6% higher in the NRC-J specimen and the NRC-JD specimen, respectively. Both NRC joint details were evaluated to secure ductility of 0.03 rad or more, the minimum total inter-story displacement angle required for the composite intermediate moment frame according to the KDS standard (KDS 41 31 00). At the slope by relative storey displacemet of 5.7%, the NRC-J specimen and the NRC-JD specimen had about 34.8% and 61.1% greater cumulative energy dissipation capacity than the RC specimen. The experimental strength of the NRC beam-column connection was evaluated to be 30% to 53% greater than the theoretical strength according to the KDS standard formula, and the standard formula evaluated the joint performance as a safety side.