• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.102-112
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• 2020

In this study, in order to design a wedge-type anchor that can hold an wide carbon plate with a width of 100 mm or more that can be used in a bridge structure, the mechanical behaviors are evaluated based on the main design variables such as the angle of the wedge and the coefficient of friction between the guide and the wedge. The stress state of the carbon plate was calculated by numerical analysis method for each design variable, and the performance of the anchor in the critical state was evaluated according to the failure criteria for composite material, and the optimal design specifications of the anchor were determined based on numerical results. The performance of the optimally designed anchor was verified through actual experiments, and the results of this study are considered to be useful for the optimal design of the CFRP plate anchor to reinforce large structures.

• Composites Research
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• v.34 no.6
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• pp.426-433
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• 2021

The carbon fiber reinforced plastic manufacturing process has a problem in that a dimensional error occurs due to thermal deformation such as residual stress, spring-in, and warpage. The main causes of thermal deformation are various, including the shape of the product, the chemical shrinkage, thermal expansion of the resin, and the mold effect according to the material and surface condition of the mold. In this study, a viscoelastic model was applied to the plate model to predict the thermal deformation. The effects of chemical shrinkage and thermal expansion of the resin, which are the main causes of thermal deformation, were analyzed, and the analysis technique of the 3-D viscoelastic model with and without mold was also studied. Then, the L-shaped mold effect was analyzed using the verified 3D viscoelastic model analysis technique. The results show that different residual deformation occurs depending on the surface condition even when the same mold is used.

• The Journal of Advanced Prosthodontics
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• v.5 no.4
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• pp.457-463
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• 2013

PURPOSE. The purpose of this study was to compare the effect of a diode laser and traditional irrigants on the bond strength of self-adhesive cement. MATERIALS AND METHODS. Fifty-five incisors extracted due to periodontal problems were used. All teeth were instrumented using a set of rotary root canal instruments. The post spaces were enlarged for a No.14 (diameter, 1.4 mm) Snowlight (Abrasive technology, OH, USA) glass fiber reinforced composite post with matching drill. The teeth were randomly divided into 5 experimental groups of 11 teeth each. The post spaces were treated with the followings: Group 1: 5 mL 0.9% physiological saline; Group 2: 5 mL 5.25% sodium hypochlorite; Group 3: 5 mL 17% ethylene diamine tetra acetic acid (EDTA), Group 4: 37% orthophosphoric acid and Group 5: Photodynamic diode laser irradiation for 1 minute after application of light-active dye solution. Snowlight posts were luted with self-adhesive resin cement. Each root was sectioned perpendicular to its long axis to create 1 mm thick specimens. The push-out bond strength test method was used to measure bond strength. One tooth from each group was processed for scanning electron microscopic analysis. RESULTS. Bond strength values were as follow: Group 1 = 4.15 MPa; Group 2 = 3.00 MPa; Group 3 = 4.45 MPa; Group 4 = 6.96 MPa; and Group 5 = 8.93 MPa. These values were analysed using one-way ANOVA and Tukey honestly significant difference test (P<.05). Significantly higher bond strength values were obtained with the diode laser and orthophosphoric acid (P<.05). There were no differences found between the other groups (P> .05). CONCLUSION. Orthophosphoric acid and EDTA were more effective methods for removing the smear layer than the diode laser. However, the diode laser and orthophosphoric acid were more effective at the cement dentin interface than the EDTA, Therefore, modifying the smear layer may be more effective when a self-adhesive system is used.

• Composites Research
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• v.15 no.6
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• pp.16-23
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• 2002

In this work, the effect of anodic oxidation on surface characteristics of high strength PAN-based carbon fibers was investigated in mechanical interfacial properties of composites. The surface properties of the carbon fibers were determined by acid-base values, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angles. And their mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). As a result, the acidity or the $O_{ls}/C_{ls}$ ratio of carbon fiber surfaces was increased, due to the development of the oxygen functional groups. Consequently, the anodic oxidation led to an increase in surface free energy of the carbon fibers, mainly due to the increase of its specific (or polar) component. The mechanical interfacial properties of the composites, including ILSS and $K_{IC}$, had been improved in the anodic oxidation on fibers. These results were explained that good wetting played an important role in improving the degree of adhesion at interfaces between fibers and epoxy resin matrix.

• Composites Research
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• v.23 no.3
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• pp.7-12
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• 2010

In order to increase the electrical conductivity and the mechanical properties of carbon fabric composites, multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) were deposited on carbon fabrics by anodic and cathodic electrophoretic deposition (EPD) processes. In the cathodic EPD, carbon nano-particles and nano-sized Cu particles were simultaneously deposited on the carbon fabric, which gave a synergetic effect on the enhancement of properties as well as the degree of deposition. The hybridization of carbon nano-particles and micron-sized carbon fiber significantly improved the through-the-thickness electrical conductivity. In addition, both MWCNTs and CNFs were deposited onto the carbon fabric for multi-scale hybrid composites. Multi-scale deposition improved the through-the-thickness electrical conductivity, compared to the deposition of either MWCNTs or CNFs.

• Composites Research
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• v.35 no.6
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• pp.469-476
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• 2022

In this paper, the microwave absorbing characteristics after the impact of the radar-absorbing structure (RAS) consisting of periodic pattern sheet (PPS) and glass fiber-reinforced plastic (GFRP) were experimentally investigated. The fabricated RAS effectively absorbed the microwave in the X-band (8.2-12.4 GHz). In order to induce the damage to the RAS, a low-velocity impact test with various impact energy of 15, 40, and 60 J was conducted. Afterward, the impact damage was observed by using visual inspection, non-destructive test, and image processing method. Moreover, the absorbing performance of intact and damaged RAS was measured by the free-space measurement system. The experiment results revealed that the delamination damage from the impact energy of 15 J did not considerably affect the microwave absorbing performance of the RAS. However, fiber breakage and penetration damage with a relatively large damaged area were occuured when the impact energy was increased up to 40 J and 60 J, and these failures significantly degraded the microwave absorbing characteristics of the RAS.

• Composites Research
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• v.22 no.6
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• pp.23-31
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• 2009

This paper investigated acoustic emission (AE) characteristics in association with various fracture processes of glass fiber reinforced plastic skin/ aluminum honeycomb core (GF-AH) hybrid composites under compressive and bending loads. Various failure modes such as skin layer fracture, skin/core interfacial fracture, and local plastic yield buckling and cell wall adhesive fracture occurring in the honeycomb cell wall were classified through the fracture identification in association with the AE frequency and amplitude analysis. The distribution of the event-rate in which it has a high amplitude showed a procedure of cell wall adhesive fracture, skin/core interfacial debonding and fiber breakage, whereas distribution of different peak frequencies indicated the plastic deformation of aluminum cell wall and the friction between honeycomb walls. Consequently, the fracture behaviors of GF-AH hybrid composites could be characterized through a nondestructive evaluation employing the AE technique.

• Composites Research
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• v.35 no.3
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• pp.201-215
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• 2022

This paper presents the development of thin and lightweight ultra-high temperature radar-absorbing ceramic composites composed of an aluminosilicate ceramic matrix-based geopolymer reinforced ceramic fiber and sendust magnetic nanoparticles in X-band frequency range (8.2~12.4 GHz). The dielectric properties with regard to complex permittivity of ceramic/sendust-aluminosilicate composites were proportional to the size of sendust magnetic nanoparticle with high magnetic characteristic properties as flake shape and its concentrations in the target frequency range. The characteristic microstructures, element composition, phase identification, and thermal stability were examined by SEM, EDS, VSM and TGA, respectively. The fabricated total thicknesses of the proposed single slab ultra-high temperature radar absorber correspond to 1.585 mm, respectively, exhibiting their excellent EM absorption performance. The behavior of ultra-high temperature EM wave absorption properties was verified to the developed free-space measurement system linked with high temperature furnace for X-band from 25℃ to 1,000℃.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.8 no.3
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• pp.579-588
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• 2018

There are the plastic resin, fiber and the single metal among materials. There is also the inhomogeneous material whose durability is improved as the composite material with the property of light weight. This study notices the composite material with light weight of CFRP. The strength properties of stainless steel and aluminum which have been used generally are compared and analyzed each other with CFRP. The compact tension specimen of the same standard by each material were designed and the simulation tensile analyses were carried out. As the study result, the maximum deformation, maximum stress and maxium strain energy are shown to be about 0.0148mm, 59.104MPa and 0.00529mJ respectively in case of CFRP specimen model. The maximum deformation, maximum stress and maxium strain energy were shown to be about 0.0106mm, 42.22MPa and 0.002699mJ respectively at stainless steel. It could be checked that the maximum deformation, maximum stress and maxium strain energy of aluminum specimen model were shown to be about 0.023mm, 33.29MPa and 0.00464mJ respectively at stainless steel. Therefore, the results at this study are thought to be applied with the basic data on the strength property of CFRP composite material.

• Elastomers and Composites
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• v.46 no.3
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• pp.211-217
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• 2011

Wood Polymer Composite (WPC) has attracted a great deal of attention in environmental industries due to renewable resources, processability, excellent physical properties and logging regulations for application to housing units and engineering construction materials. In this study, commercial WPCs were prepared by using a modular intermeshing co-rotating twin screw extruder. The effect of three main factors such as wood flour contents, coupling agent concentrations and pre-treatment of wood flour on the properties of WPCs was extensively investigated. It was found that tensile strength and thermal stability were decreased with increasing wood flour contents whereas the water absorption was increased. Addition of maleic anhydride grafted polypropylene (PP-g-MA) into WPC exhibited better physical properties. On the contrary, the water absorption was slightly decreased with PP-g-MA. Finally the sample, which was prepared with pre-treated wood flour, represented the highest tensile strength. However, the water absorption of the sample was increased due to the transition of crystalline structure of cellulose.