• Journal of Adhesion and Interface
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• v.11 no.4
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• pp.174-180
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• 2010

The effect of carbon nanotube surface treatment on the interface and thermal conductivity of carbon nanotube-based poly(methylmethacrylate) (PMMA) composites was investigated. Coagulation and atomic-transfer radical polymerization (ATRP) was applied to modify the surface of multi-wall carbon nano-tube. The composite of ATRP method used carbon nanotube showed the higher transparency and thermal conductivities than that of the coagulation method used. In comparison to the thermal conductivity of pure PMMA, 0.21 W/mK, the ATRP carbon nanotube used PMMA/MWNT composite showed a thermal conductivity of 0.38 W/mK. The interface between carbon nanotube and PMMA was observed by scanning electron microscope and uniform dispersion of carbon nanotube was observed without any void in the PMMA matrix. It may be beneficial to transport the phonon without any scattering and it may result in a higher thermal conductivity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.153-160
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• 2013

An orthotropic magneto-rheological rubber composite (MRRC) based on a general-purpose rubber can be manufactured by using an electromagnetic device during the curing processes of rubber mixtures. The magnetic transmissivity of MRRCs increases with the iron particle (IP) content, and that of aligned MRRCs with a 2-T magnetic field is 1.8 to 2 times higher as compared to that of randomly dispersed MRRCs. The effect of a 2-T magnetic field on carbon nanotube (CNT) reinforced MRRC has been identified clearly, and the magnetic transmissivity is found to be 3.7%. The compressive stress of MRRC (IP 90 + CNT 5, 2 T alignment) under a magnetic field of 0.49 T is 2.1 times higher as compared to that of the matrix. The MR effect of MRRC increases with the IP content, and that of aligned MRRC with the IP 90 and 2 T magnetic field is 20.4%. It is confirmed that the magnetic field when making the specimen and when performing the compression test greatly impacts the compression characteristics.

• Composites Research
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• v.13 no.1
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• pp.89-97
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• 2000

Fatigue damage detection and vibration sensing for a laminated composites and impact location detection for a steel beam have been carried out using optical fiber sensor. Intensity based optical fiber sensor is constructed by placing two cleaved fiber end in a hollow glass tube, and multiple reflection within the cavity is considered. Fatigue signals are measured by embedded optical fiber, surface mounted optical fiber sensor and strain gage simultaneously. For vibration sensing, optical fiber sensor is mounted on the carbon fiber composite beam and its response to free vibration and forced vibration is investigated. In impact location detection, two optical fiber sensors are used and the information obtained from two sensors is arrival time delay of vibration caused by impact. Impact location can be calculated from this time delay. The obtained results show that the intensity based optical fiber sensor provide reliable data during long-term fatigue loading, unlike strain gage which deteriorate during the early part of the fatigue test. Optical fiber sensor signals coincide with gap sensor in vibration sensing. The precise locations of impact can be detected within 4.1% error limit.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.7
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• pp.561-568
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• 2013

After we designed Bearingless rotor hub system for 7,000lb class helicopter, flexbeam fatigue analysis was conducted for validation of requirement life time 8,000 hours. sectional structural analysis method applying elastic beam model was used. Fatigue analysis for two sections of flexbeam which were expected to weak to fatigue damage from result of static analysis was conducted. Extension, bending and torsion stiffness of flexbeam section shape was calculated using VABS for structure analysis. S-N curve of two composite material which composed flexbeam was generated using wohler equation. Load analysis of bearingless rotor system was conducted using CAMRAD II and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used flexbeam fatigue safe life analysis.

• Composites Research
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• v.13 no.5
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• pp.1-9
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• 2000

An intensity-based optical fiber vibration sensor is applied to monitor the structural vibration and detect impact locations on a plate. Optical fiber vibration sensor is constructed by placing two cleaved fiber end, one of which is cantilevered in a hollow glass tube. The movement of the cantilevered section lags behind the rest of the sensor in response to an applied vibration and the amount of light coupled between the two fibers is thereby modulated. For vibration sensing, optical fiber vibration sensor is mounted on the carbon fiber composite beam and its response is investigated to free and forced vibration. In impact location detection, four optical fiber vibration sensors whose location is predetermined are placed at chosen positions and the different arrival times of impact-generated vibration signal are recorded by an FFT analyzer. Impact location can be calculated from these time delays. Experimental results show that optical fiber vibration sensor signals coincide with gap sensor in vibration sensing. The precise location of impact can be detected on an acrylate plate.

• Journal of Powder Materials
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• v.22 no.4
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• pp.283-288
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• 2015

Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-TiC composite powders which are fabricated by high-energy ball-milling. A powder mixture of Fe and TiC is prepared in a planetary ball mill at a rotation speed of 500 rpm for 1h. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts show incomplete densification with a relative denstiy of 86.1% after sintering at $1300^{\circ}C$ for 3h. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly complete densification of 98.6% relative density under the sintering pressure of 50 MPa.

• Restorative Dentistry and Endodontics
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• v.16 no.1
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• pp.200-208
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• 1991

The purpose of this study was to observe shear bond strength of composite resin to dentin following surface treatment. Freshly extracted forty-eight sound human molars were used in this study. They were stored at $4^{\circ}C$ physiologic saline solution before experiment. The teeth was then mounted with self curing acrylic resin in brass mold. The buccal surfaces of the teeth were grinding approximately 1.5mm by means of water-irrigated grinding wheel to expose the flattened fresh dentin surfaces. The specimens were divided into 6 groups according to preparation and treatment procedures on dentin surfaces; Group 1: Untreated after preparation with No.301 diamond point Group 2: Treated with primer for 60 seconds after preparation with No.301 diamond point Group 3: Untreated after preparation with No.700 fissure carbide bur Group 4: Treated with primer for 60 seconds after preparation with No.700 fissure carbide bur Group 5: Untreated after grinding with 600 grit silicon carbide paper Group 6: Treated with primer for 60 seconds after grinding with 600 grit silicon carbide paper Light cure dental adhesive was applicated to each specimen. Silux plus(3M) was inserted then into polyethylene tube of 3mm diameter and 3mm height, and polymerized to dentin surface. All of the specimens were stored in distilled water at $35.6^{\circ}C$ for 24 hours prior to testing. The shear bond strength was measured using an Instron Universal Testing Machine. The results obtained from this study were as follows: 1. The shear bond strength to dentin was the highest in group II. 2. The shear bond strength to dentin was the lowest in group III. 3. There was no significant difference in shear bond strength to dentin according to preparation instrument. 4. The primer treatment group showed significantly greater shear bond strength than untreated group.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.2
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• pp.66-74
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• 2021

Cladding material, which can selectively obtain excellent properties of different metals, is a composite material that combines two or more types of dissimilar metals into one plate. The titanium-copper cladding material between titanium which has excellent corrosion resistance and copper which has high thermal and electrical conductivity, are highly valuable composite materials. It can be used as heat exchangers with high conductivity under severe corrosion conditions. In order to apply the clad plate to the heat exchanger, it must be manufactured in the form of a tube and additional welding is required. It is important to select the cladding material manufacturing process and the welding process. The process of manufacturing the cladding material includes extrusion, rolling, and explosive bonding. Among them, the explosive bonding process is suitable for additional welding because no heat-affected zone is formed. In this study TIG welding of the explosive-bonded dissimilar clad plates was successfully performed by butt welding. The microstructures and bonding interface of the welded part were observed, and the effect of the bonding layer at the welding interface and the intermetallic compounds on the mechanical properties and tensile plastic deformation behaviors were analyzed. And also the integrity of TIG-welded dissimilar part was evaluated.

• Steel and Composite Structures
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• v.46 no.6
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• pp.793-804
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• 2023

In this study, cyclic loading tests were conducted to assess the seismic performance of cast-in-place (CIP) concrete-filled hollow core precast concrete columns (HPCC) constructed using steel ducts and rubber tubes. The outer shells of HPCC, with a hollow ratio of 47%, were fabricated using steel ducts and rubber tubes, respectively. Two combinations of shear studs & long threaded bars or cross-deformed bars & V-ties were employed to ensure the structural integrity of the old concrete (outer shell) and new CIP concrete. Up to a drift ratio of 3.8%, the hysteresis loop, yielding stiffness, dissipated energy, and equivalent damping ratio of the HPCC specimens were largely comparable to those of the solid columns. Besides the similarities in cyclic load-displacement responses, the strain history of the longitudinal bars and the transverse confinement of the three specimens also exhibited similar patterns. The measured maximum moment exceeded the predicted moment according to ACI 318 by more than 1.03 times. However, the load reduction of the HPCC specimen after reaching peak strength was marginally greater than that of the solid specimen. The energy dissipation and equivalent damping ratios of the HPCC specimens were 20% and 25% lower than those of the solid specimen, respectively. Taking into account the overall results, the structural behavior of HPCC specimens fabricated using steel ducts and rubber tubes is deemed comparable to that of solid columns. Furthermore, it was confirmed that the two combinations for securing structural integrity functioned as expected, and that rubber air-tubes can be effectively used to create well-shaped hollow sections.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1A
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• pp.19-30
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• 2009

The primary objective of the present study was to attempt to quantify the effect of the existing codes for CFT composite section on initial section flexural stiffness, based on the measured vibration frequency of CFT truss girders. The formulae for the initial flexural stiffness of the composite sections in the different codes are compared with the free vibration test results. The results of the free vibration test on the CFT truss girders are in good agreement with the analysis results when used in ACI formulae. The free vibration analysis of CFT truss girders for different f/L ratios was conducted to determine how the natural frequency of the CFT truss girder is affected by different f/L ratios. The presence of the f/L ratios in CFT truss girders alters its frequencies of vibration because of the global stiffness of the CFT girders. The frequency in horizontal modes decreases as the f/L ratio increases. However, the frequency in vertical modes increases as the f/L ratio increases.