• Polymer(Korea)
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• v.28 no.4
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• pp.285-290
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• 2004

Nondestructive damage sensitivity of carbon nanotube(CNT) and nanofiber (CNF)/epoxy composites with their adding contents was investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison with CNT and CNF. The fracture of carbon fiber was detected by acoustic emission (AE), which was correlated to the change in electrical resistance, ΔR under double-matrix composites (DMC) test. Stress sensing on carbon nanocomposites was performed by electro-pullout test under uniform cyclic loading. At the same volume fraction, the damage sensitivity for fiber fracture, matrix deformation and stress sensing were highest for CNT/epoxy composite, whereas for CB/epoxy composite they were the lowest among three carbon nanomaterials (CNMs). Damage sensitivity was correlated with morphological observation of carbon nanocomposites. Homogeneous dispersion among CNMs could be keying parameters for better damage monitoring. In this study, damage sensing of carbon nanocomposites could be evaluated well nondestructively by the electrical resistance measurement with AE.

• Membrane Journal
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• v.22 no.1
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• pp.35-45
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• 2012

We prepared the highly ordered nano-wires of polypyrrole, polyaniline conductive polymers and polypyrrole/ polyaniline conductive copolymers by templating the anodic aluminum oxide (AAO) porous membrane, in which pore diameter was 20 nm, 100 nm and 200 nm. Those conductive polymers were grown from pore inner surface of AAO membrane forming hollow tubes and then wire structures were formed after 3 hour polymerization. By removing AAO membrane templates using sodium hydroxide solution, the conductive polymer nano-wires were successfully obtained, of which diameter and length were close to the ones of nano-pores in AAO membrane template. Crystallinity and thermal stability of the conductive polymer nano-wires were higher than irregular ones that prepared by solution polymerization. Furthermore, the electrical resistance of conductive polymer nano-wires were reduced by about 4~60% compared with that of the irregular polymers prepared by solution polymerization.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.10
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• pp.19-26
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• 2021

In fine-particle injection processing, hard fine particles, such as silicon carbide or aluminum oxide, are injected - using high-pressure air, and a small amount of material is removed by applying an impact to the workpiece by spraying at high speeds. In this study, a two-axis stage device capable of sequence control was developed to spray various shapes, such as circles and squares, on the surface during the micro-particle jetting process to understand the surface-shape micro-particle-processing characteristics. In the experimental device, two stepper motors were used for the linear movement of the two degree-of-freedom mechanism. The signal output from the microcontroller is - converted into a signal with a current sufficient to drive the stepper motor. The stepper motor rotates precisely in synchronization with the pulse-signal input from the outside, eliminating the need for a separate rotation-angle sensor. The major factors of the processing conditions are fine particles (silicon carbide, aluminum oxide), injection pressure, nozzle diameter, feed rate, and number of injection cycles. They were identified using the ANOVA technique on the design of the experimental method. Based on this, the surface roughness of the spraying surface, surface depth of the spraying surface, and radius of the corner of the spraying surface were measured, and depending on the characteristics, the required spraying conditions were studied.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.305-312
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• 2021

This study examines the damage to the submarine's escape trunk hatch spring through microstructure analysis. The cause of the escape trunk's damage during the submarine's construction and its improvement measures were reviewed. To determine the cause of breakage of the escape trunk spring, samples were taken from the damaged product and analyzed for chemical composition, hardness, and microstructure. In particular, the breakage part of the spring was analyzed in-depth by using a scanning electron microscope to determine the cause of corrosion destruction. Finally, a spring shape design method was proposed through the investigation of the cause of spring breakage. In addition, a newly improved spring was produced by applying a nylon coating with excellent corrosion resistance and abrasion resistance. Applying to an actual submarine trunk hatch revealed that the coating peeling phenomenon due to the contact between the springs is significantly improved when the hatch is opened or closed compared to the existing products.

• Journal of the Korea Institute of Building Construction
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• v.21 no.4
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• pp.269-279
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• 2021

Palm Oil Fuel Ash(POFA) has been widely used to replace Portland cement to enhance the mechanical properties and durability of concrete. However, it reduces the workability of concrete due to the high content of unburnt carbon and its angular shape requiring the usage of superplasticizer to ensure a proper flowability. In this study, effects of different types and dosage of superplasticizer on the early mechanical and hydration properties of cement paste containing micro-POFA were evaluated using mini-slump test, early compressive strength, TGA, XRD, and SEM. The results indicated that the flowability of cement paste containing micro-POFA reduced as the replacement ratio of micro-POFA increased. As the dosage of superplasticizer increased, the flowability was also increased. In addition, the usage of superplasticizer reduced the early compressive strength, and the strength decreased with an increase in the dosage of superplasticizer. It was confirmed that superplasticizer hindered the formation of C-S-H leading to a relative increase in the formation of Ca(OH)₂.

• Tribology and Lubricants
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• v.40 no.2
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• pp.61-66
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• 2024

Micro-plastics are synthetic high-differentiation chemicals of less than 5mm in size, and are deposited not only on the sea surface but also on the coast. If these micro-plastics are not properly separated from the sand, they can threaten marine ecosystems. Thus, in the present study, we aimed to apply cyclone separator to the micro-plastic retrieval in order to predict the movement of particles according to the formation of the cyclone separator by applying the centrifugal force of the particle in accordance with the rotational movement of the air. The cyclone separator has three shapes, the first one is a typical interconnected cyclone separator. The second is the horn form, except for the cylinder in a regular cyclone separator, and the third is a form that increases the horn's height twice in the second. The numerical analysis simulation of the Cyclone separator used the Fluent software package. The output speed of the Cyclone separator was 5 to 13m/s at 1m/s intervals. The simulated particles include sand, Styrofoam, PET, PP, and PU. Sand particles are assigned a fixed diameter of 2mm, while other particles have a diameter of 3mm. As a result of the analysis, the first form was not separated from plastic. The Styrofoam separation efficiency in the second showed its highest efficiency at 72.7% at 7m/s, and the efficiency decreased after 12m/s as the sand particles were mixed into the plastic attachment location. In the third form, the separation efficiency of Styrofoam at 12m/s was highest at 67.9%.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.511-520
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• 2004

The fracture energy evaluated from the previous experimental results can be simulated by using the modified singular fracture process zone (S-FPZ) model. The fracture model has two fracture properties of strain energy release rate for crack extension and crack close stress versus crack width relationship $f_{ccs}$ ( w ) for fracture process zone (FPZ) development. The $f_{ccs}$( w ) relationship is not sensitive to specimen geometry and crack velocity. The fracture energy rate in the FPZ increases linearly with crack extension until the FPZ is fully developed. The fracture criterion of the strain energy release rate depends on specimen geometry and crack velocity as a function of crack extension. The variation of strain energy release rate with crack extension can explain theoretically the micro-cracking, micro-crack localization and full development of the FPZ in concrete.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.321-326
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• 2002

ZnWO$_4$ nano-powders were successfully prepared by polymerized complex method using zinc nitrate and tungstic acid as starting materials. In order to investigate the thermal decomposition and crystallization process, the polymeric precursors were heat-treated at temperatures from 300 to 600$^{\circ}$C for 3 h, and the heat-treated powders were characterized by XRD and FTIR. The surface morphology of the heat-treated powders were observed using SEM and TEM. The crystallite size was measured by X-ray analysis. Crystallization of the ZnWO$_4$ powders were detected at 400$^{\circ}$C and entirely completed at a temperature of 600$^{\circ}$C. The particles heat-treated 400 and 500$^{\circ}$C showed primarily co-mixed morphology with spherical and silkworm-like forms, while the particles heat-treated at 600$^{\circ}$C showed more homogeneous morphology. The average crystalline size were 19.9∼24.nm showing an ordinary tendency to increase with the temperatures from 400 to 600$^{\circ}$C.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1119-1126
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• 2012

The collective behavior of bacteria plays an important role in biofilm development. In this study, the fluidic properties of biofilms formed in Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) colonies were compared by visualizing 200-nm fluorescent beads that were initially embedded in an agar plate and distributed spontaneously on the upper surface of the growing colonies. We conducted experiments to measure the three-dimensional profile of the E. coli colony using fluorescent microbeads that did not flow in the colony. Vortical flow patterns near the edge of the B. subtilis colony were observed clearly by tracking the movement of the beads in the biofilm of the colony. The present study should be the first step toward determining the effect of fluidic biofilms on the growth and swarming dynamics of bacteria.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.479-484
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• 2009

Nondestructive evaluation(NDE) of ceramic matrix composites is essential for developing reliable ceramics for industrial applications. In the work, C-Scan image analysis has been used to characterize surface crack of SiC ceramics nondestructively. The possibility of detection of surface crack were carried out experimentally by two types of ultrasonic equipment of SDS-win and $\mu$-SDS, and three types of transducer of 25, 50 and 125 MHz. A surface micro-crack of ceramics was not detected by transducer of 25 MHz and 50 MHz. Though the focus method was detected dimly the crack by transducer of 125 MHz, the defocus method could detect the shape of diamond indenter. As a whole, the focus method and the defocus method came to the conclusion that micro crack have a good possibility for detection.