• Composites Research
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• v.17 no.1
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• pp.10-17
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• 2004

In this work, the blend system prepared from epoky(DGEBA)/polymethylmethacrylate(PMMA) was investigated in thermal and mechanical interfacial property measurements. The thermal properties were carried out by DSC, DMA, and TGA measurements. Also, the surface free energy and fracture toughness were determined by contact angle and critical stress intensity factor($K_{IC}$), respectively. And the fracture surface was observed by SEM after $K_{IC}$ tests. As experimental results, the curing temperature and glass transition temperature were slightly increased in addition of PMMA. Surface free energy of the blends showed an improved value at low contents of PMMA which could be attributed to the both increasings of London dispersive and polar components. From measurement of $K_{IC}$ of the blends, the highest value was found at 5 phr. This was due to the increasing of compatibility or physical interaction in macromolecular chains between DGEBA and PMMA of the blends.

• Composites Research
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• v.18 no.4
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• pp.14-20
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• 2005

To determine the effect of chemical structure of aromatic amino curing agents on thermal and mechanical properties, standard epoxy resin DGEBF (diglycidylether of bisphenol F) was cured with diaminodiphenyl methane (DDM) and diaminodiphenyl sulphone (DDS) in a stoichiometrically equivalent ratio. From this work the effect of aromatic amino curing agents on the thermal and mechanical properties is significantly influenced by the chemical structure of curing agents. In contrast, the results show that the DGEBF/DDS system having the sulfone structure between the benzene rings had higher values in the thermal stability, density, shrinkage ($\%$), thermal expansion coefficient, tensile modulus and strength, flexural modulus and strength than the DGEBF/DDM system having methylene structure between the benzene rings, whereas the DGEBF/DDS system presented low values in maximum exothermic temperature, conversion of epoxide, and grass transition temperature. These results are caused by the relative effects of sulfone group having strong electronegativity and methylene group having (+) repulsive property. The result of fractography shows that the grain distribution of DGEBF/DDS system is more irregular than that of the DGEBF/DDM system.

• Applied Chemistry for Engineering
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• v.9 no.1
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• pp.66-70
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• 1998

Several liquid crystalline monomers were synthesized and characterized to utilize as new matrix materials of liquid crystal/polymer composite films for display application. Liquid crystalline compounds which have azo group as center link, cyano group at one of the terminal position in common and bromoalkyl(azo(n)), azidoalkyl(AZI(n)), aminoalkyl(ALC(n)) as the terminal group were synthesized and identified respectively by FT-lR, $^1H-NMR$ spectrometer and elemental analysis. All these compounds exhibited nematic liquid crystalline region in the certain temperature range as determined by DSC and polarized optical microscope. These liquid crystalline compounds also showed a typical even-odd effect in both $T_{KN}$ and $T_{NI}$ due to conformational change as the length of terminal alkyl chain, $-(CH_2)n-$. was varied.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.354-360
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• 2002

The piezoelectric composites had many advantages in comparison with conventional piezoelectric ceramics and piezopolymers for ultrasonic transducers used in NDT and in medical ultrasionic imaging. The electromechanical coupling coefficient should be high and the acoustic impedance should be low in these applications. However, the cross-coupling with spurious oscillations caused by laterally running plate waves exhibited complex motions in the surface of piezoelectric composites with coarse lateral spatial scale. The thickness mode electromechanical coupling coefficient of 1-3type of piezoelectric compoistes were 0.36 to 0.64, and the acoustic impedance of them were 9.8 to 22.7 MRayl. The lateral resonance frequency of 1-3 type piezoelectric composites shifted to high frequency region with decreasing lateral spatial scale.

• 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.17 no.6
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• pp.37-43
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• 2004

To determine the effect of chain length and chemical structure of linear amine curing agents on thermal and mechanical properties, a standard bifunctional linear DGEBF epoxy resin was cured with EDA and HMDA having amine group at the both ends of main chain in a stoichiometrically equivalent ratio in condition of preliminary and post cure. From this work, the effect of linear amine curing agents on the thermal and mechanical properties is significantly influenced by numbers of carbon atoms of main chain. In contrast, the results show that the DCEBF/EDA system having two carbons had higher values in the thermal stability, density, shrinkage (%), grass transition temperature, tensile modulus and strength, flexural modulus and strength than the DGEBF/HMDA system having six carbons, whereas the DGEBF/EDA cure system had relatively low values in maximum ekothermic temperature, maximum conversion of epoxide, thermal expansion coefficient than the DGEBF/HDMA cure system. These findings indicate that the packing capability (rigid property) in the EDA structure affects the thermal and mechanical properties predominantly. It shows that flexural fracture properties have a close relation to flexural modulus and strength.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.7-12
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• 2007

Previously study on structural design of the main wing of the twenty-seat class WIG (Wing in Ground Effect) craft. In the final design, three spars construction was selected for safety in the critical flight load, and the Carbon-Epoxy material was selected for lightness and structural stability. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the Y-mode (lateral mode), the Z-mode (vertical mode) and the $M_{xyz}$-mode (twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the X-mode (longitudinal mode) with the oscillating propeller thrust which occurs in operation.

• Steel and Composite Structures
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• v.22 no.5
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• pp.1019-1038
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• 2016

The use of high-strength concrete (HSC) in precast concrete segmental bridges (PCSBs) can minimize the superstructure geometry and reduce beam weight, which can accelerate the construction speed. Dry joints between the segments in PCSBs introduce discontinuity and require special attention in design and construction. Cracks in dry joints initiate more easily than those in epoxy joints in construction period or in service. Due to the higher rupture strength of HSC, the higher cracking resistance can be achieved. In this study, shear behavior of dry joints in PCSBs was investigated by experiments, especially focusing on cracking resistance and shear strength of HSC dry joints. It can be concluded that the use of HSC can improve the cracking resistance, shear strength, and ductility of monolithic, single-keyed and three-keyed specimens. The experimental results obtained from tests were compared with the AASHTO 2003 design provisions. The AASHTO 2003 provision underestimates the shear capacity of single-keyed dry joint C50 and C70 HSC specimens, underestimates the shear strength of three-keyed dry joint C70 HSC specimens, and overestimates the shear capacity of three-keyed dry joint C50 HSC specimens.

• Composites Research
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• v.28 no.5
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• pp.285-290
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• 2015

Multiscale multiphysics in structural batteries make mechanical property testing difficult. In this research, the effect of electrolyte-coating on the mechanical performance of carbon fabric was studied using a suitable mechanical test method for structural batteries. For this experiment, two types of specimens were determined their dimension according to ASTM. One type of specimen was smaller than the standard dimension. The specimens were coated by spreading the electrolyte material on carbon fabric, hardened using epoxy, and tested for tensile properties using universal testing machine. As a result, it was found that the mechanical properties of carbon fabric were not influenced by electrolyte coating. In addition, the small-scale specimen used in this experiment was determined to be sufficiently reliable.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.146-153
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• 1996

A SCARA type direct drive robot which can be used in the assembly operation was designed and manufactured. Graphite fiber epoxy composite material was used in the fabrication of the robot arm structure in order to improve the speed of the robot arm with a high damping effect. For model-based control and sensitivity analysis of system parameters, the dynamic model of robot arm and drive servo amplifier parameters such as equivalent gains of PWM driver and velocity gains of servo system were estimated from frequency response tests. The complete dynamic model for overall robot system was used in the simulation of the open-loop control. The simulation results agreed reasonably well to the experimental results. The feedforward control using the dynamic models improved the trajectory tracking performance, decreasing the tracking error by factor of three compared with PID control. This study found that the inverse dynamic model of the robot arm including the drive servo system showed better performances than the case of arm dynamic model only.