• Steel and Composite Structures
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• v.26 no.4
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• pp.421-437
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• 2018

Free vibration analysis of a three-layered microbeam including an elastic micro-core and two piezo-magnetic face-sheets resting on Pasternak's foundation are studied in this paper. Strain gradient theory is used for size-dependent modeling of microbeam. In addition, three-unknown shear and normal deformations theory is employed for description of displacement field. Hamilton's principle is used for derivation of the governing equations of motion in electro-magneto-mechanical loads. Three micro-length-scale parameters based on strain gradient theory are employed for prediction of vibrational characteristics of structure in micro-scale. The results show that increase of three micro-length-scale parameters leads to significant increase of three natural frequencies especially for increase of second micro-length-scale parameter. This result is according to this fact that stiffness of a micro-scale structure is increased with increase of micro-length-scale parameters.

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.103-114
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• 2000

Recently, the need for strengthening reinforced concrete and prestressed concrete structure is increasing, particularly when there is an increase in load requirements, a change in use, a degradation problem, or some design/construction defects. Therefore, use of composite materials for structural repair presents several advantages and has been investigated all over the world. In this paper, the reinforced concrete slabs with epoxy - bonded AFRP sheed were experimentally investigated. Experimental data on strength. stiffness, material strain, deflection and mode of failure of strengthened slabs were obtained, and comparisons between the different flexural reinforcing schemes and reinforced concrete slabs without AFRP sheets were made It can be concluded that flexural strength of RC slabs strengthened with AFRP has increased, and that ductility of strengthened slabs has decreased.

• Journal of the Korean Ceramic Society
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• v.30 no.2
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• pp.139-147
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• 1993

Two sheets of high strength cement paste using ordinary Portland cement and water soluble polymer (polyacrylamide) were made by kneading with a twin roll mill. A carbon fiber layer out between two sheet of the cement paste, and then carbon fiber reinforced high strength cement composites were prepared by pressing them. The mechanical properties of the composites were investigated through the observation of the microstructure and the application of fracture mechanics. When the carbon fiber was added with 0.2 and 0.3wt% to the composites the flexural strength and Young's modulus were about 110∼116MPa and 74∼77GPa respectively, and critical stress intensity was about 3.14MPam1/2. It can be considered that the strength improvement of high strength cement fiber composites may be due to the removal of macropores and the increase of various fracture toughness effects; grain bridging, frictional interlocking, polymer fibril bridging and fiber bridging.

• Composites Research
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• v.31 no.5
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• pp.202-208
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• 2018

In this paper, mechanical and hygroscopic properties of teak sawdust and recycled polypropylene (RPP) composites are evaluated and compared with virgin polypropylene (VPP) matrix based composites. Verities of composites are prepared by variation in the plastic types, wood plastic ratio and the addition of coupling agent in the formulations. Mixing of wood sawdust and polypropylene is done by a twin screw extruder, and then sheets of wood plastic composites (WPCs) are produced by using the compression molding method. The results show that recycled matrix composites exhibit better tensile, flexural strength with low impact strength than virgin matrix based composites. Recycled composites show low water absorption and thickness of swelling than virgin matrix based composites. The results confirm that wood content in the polymer matrix affects the performance of composites while presence maleated polypropylene (MAPP) improves the properties of the composites significantly. Developed RPP matrix composites are as useful as VPP matrix composites and have the potential to replace the wood and plastics products without any adverse effect of the plastics on the environment.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.537-542
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• 2003

The stress-strain curve of concrete confined with both spiral and carbon fiber sheet(CFS) is different to that of concrete confined with only spiral or CFS. The objective of this study is to investigate the stress-strain relation of concrete confined by composite material. In this study, 24 concrete cylinders were tested. The main variable of the cylinders was the content rate of spiral to CFS. The test results indicated that while the compressive strength of cylinder confined with both spiral and CFS increased proportionally to the aided amount of two materials, the maximum strain of cylinder depended on the larger strain of spiral or CFS.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2073-2079
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• 2008

This study aims to investigate the residual strength of sandwich composites with Al honeycomb core and carbon fiber face sheets after the quasi-static indentation damage by the experimental investigation. The 3-point bending test and the edge-wise compressive strength test were used to find the mechanical properties. The quasi-static point load and damaged hole was applied to introduce the simulated damage on the Each damaged specimens were finally assessed by the 3-point bending test and the compressive strength test. The investigation results revealed the residual strength of the damaged specimens due to the quasi-static indentation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.2
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• pp.93-102
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• 2001

The objective of this experimental study is to evaluate the strengthening effects of concrete compression confined with Epoxy-boned compound fiber sheets. An analytical model is proposed to construct a stress-strain relationship for confined concrete. Test results are summarized as followed. While non-FRP lateral confinement specimens appeared sudden failure after shell concrete was torn off, specimens confined laterally with FRP were showed that their failure. Specially, Glass fiber lateral confined specimens occurred obviously increase ductility ability. Hence, concrete specimen with lateral confinement by Hi-carborn and Aramide. Glass fiber simultaneously can be increased in not only strength but also a lot of ductility ability.

• Corrosion Science and Technology
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• v.6 no.2
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• pp.68-73
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• 2007

The toxicity of chromium that is used to impart corrosion resistance to galvanized steel created environmental and health-related concerns and generated a great deal of interest in developing chrome-free treatment coatings. In the present work, organic-inorganic composite coatings were used to coat electrogalvanized steel (EG) sheets for corrosion protection without degrading its weldability property. The new coatings composed of specially modified polyurethane dispersion hybridized with silicate and unique inorganic-organic inhibitors were developed during this work. It was found that about $1{\mu}m$ thickness of coating layer is secure enough in corrosion resistance of flat and formed part even after alkaline degreasing. Overall chemical resistances including fingerprint resistance and paint adhesion property were satisfied with the test specification of Sony technical standard of SS-00260-2002. Therefore, it is concluded that the newly developed chrome-free product can replace the conventional chromated product.

• Steel and Composite Structures
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• v.27 no.2
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• pp.135-147
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• 2018

Quasi-static three-point bending tests on sandwich beams with expanded metal sheets as core were conducted. Relationships between the force and displacement at the mid-span of the sandwich beams were obtained from the experiments. Numerical simulations were carried out using ABAQUS/EXPLCIT and the results were thoroughly compared with the experimental results. A parametric analysis was performed using a Box-Behnken design (BBD) for the design of experiments (DOE) techniques and a finite element modeling. Then, the influence of the core layers number, size of the cell and, thickness of the substrates was investigated. The results showed that the increase in the size of the expanded metal cell in a reasonable range was required to improve the performance of the structure under bending collapse. It was found that core layers number and size of the cell was key factors governing the quasi-static response of the sandwich beams with lattice cores.

• Advances in nano research
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• v.8 no.2
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• pp.103-114
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• 2020

In this research, buckling and free vibration of rectangular polymeric laminate reinforced by graphene sheets are investigated. Various patterns are considered for augmentation of each laminate. Critical buckling load is evaluated for different parameters, including boundary conditions, reinforcement pattern, loading regime, and laminate geometric states. Furthermore, vibration analysis is investigated for square laminate. Elastic properties of the composite are calculated using a combination of both molecular dynamics (MD) and the rule of mixture (MR). Kinematics of the plate is approximated based on the first shear deformation theory (FSDT). The current analysis is performed based on the energy method. For the numerical investigation, Ritz method is applied, and for shape functions, Chebyshev polynomials are utilized. It is found that the number of layers is effective on the buckling load and natural frequency of laminates which made from non-uniform layers.