• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.8
• /
• pp.378-385
• /
• 2017

This study investigated the design of a snap fit, which is widely used for fastening plastic parts. We analyzed the assembly mechanism of a lock snapfit, measured the assembly force and separation force based on the design of experiments, and derived a regression equation through an analysis of variance. The response surface methodology was also used. Polybutylene terephthalate was used to fabricate specimens, and the assembly force and separation force were measured using a micro-tensile tester. The length, width, thickness, and interference were considered as factors. A second-order regression model was used to derive the regression equation. The assembly force decreased with increasing length and width, but it increased with increasing thickness and interference. The finite element method was used to analyze the assembly mechanics. The width decreased the assembly force by increasing the ductility. The influences of the factors for low assembly force and high release force were shown to be opposite to each other. It was necessary to design a structure that minimized the assembly force while maintaining an appropriate level of separation force.

• Polymer(Korea)
• /
• v.28 no.5
• /
• pp.404-411
• /
• 2004

The microcapsules containing triphenyl phosphate (TPP), a flame retardant, were prepared by phase-inversion emulsification technique using the epoxy resin (Novolac type) with excellent physical properties and network structure. This microencapsulation process was adopted for the protection of TPP evaporation and wetting of polymer composite during the polymer blend processing. The TPP, epoxy resin and mixed surfactants were emulsified to oil in water (O/W) by the phase inversion technology and then conducted on the crosslinking of epoxy resin by in-situ polymerization. The capsule size and size distribution of TPP capsules was controlled by mixed surfactant ratio, concentration and TPP contents, The formation and thermal property of TPP capsules were measured by differential scanning calorimetry and thermogravimetric analysis. The morphology and size of TPP capsules were also investigated by scanning and transmission electron microscopies. As the surfactant concentration increased, the TPP capsules were more spherical and mono-dispersed at the same weight ratio of mixed surfactants (F127: SDBS).

• Journal of the Korean Wood Science and Technology
• /
• v.42 no.3
• /
• pp.258-265
• /
• 2014

By replacing the previous metal connector on the joints of timber structure, the GFRP reinforced laminated wooden pin was produced using a wooden material and Glass fiber reinforced plastic(GFRP) composite laminate. In addition, using the reinforced wooden pin, the tensile type shear strength test was conducted. Based on the result of the bending strength test of the reinforced laminated wooden pin according to the GFRP arrangement, a specimen(Type-A) with a single insertion of GFRP for each layer have shown the most favorable performance. Also, it was verified that densified specimen hot pressed for an hour at the temperature of $150^{\circ}C$ and with the oppression pressure $1.96N/mm^2$ have shown the improved performance of 1.57 times than the specimen without the densification. And in the bending strength test considering the load direction, edgewise have shown a higher performance of 3.51 times than the flatwise. A shear strength test was conducted using the Type-A reinforced laminated wooden pin which have shown a moderate performance on the test. Based on the test conducted by differentiating the type of the joint plate and the connector, compared to the specimen(Type-DS) applied with the drift pin and steel plate, the specimen( Type-WL) applied with the GFRP reinforced laminated wooden pin and GFRP reinforced wooden laminated plate have shown 1.12 times higher shear strength and also have shown an excellent toughness even after the maximum load.

• Restorative Dentistry and Endodontics
• /
• v.21 no.2
• /
• pp.619-627
• /
• 1996

There are increasing use of composite resin in the posterior teeth and the new indirect inlay technique was introduced for compensating much troubles faced in direct technique. Many researchers insisted that overall properties of restorative materials were enhanced by an additional curing but this technique still has a problems about using cement material. Resin inlay obtains retention force from friction and another adhesion to tooth structure. A shape of cavity preparation was noted but studies about cement thickness and bond strength with cavity divergency are rare. The purpose of this study is to assess the effect of cavity divergency on cement thickness and bond strength of resin inlay. Cavities, which divergency was $6^{\circ}$, $16^{\circ}$, and $26^{\circ}$ in each group, were prepared and their divergency was verified by Adobe Photoshop program through the image capture with stereo microscope and FlexCam. Inlays were fixed into the cavities with a resin cement, Superbond and were handled under chemical (in 75% ethanol for 24 hrs.) and thermal stress (500 cycles from $5^{\circ}$ to $55^{\circ}C$). MXT 70 (x400) was used for measuring the cement thickness and bond strength was evaluated with a universal testing machine. Following results were obtained : 1. The cement thickness in Mean (S.D.) were; 35.58 (10.31)${\mu}m$ in $6^{\circ}$ group, 35.97 (10.49)${\mu}m$ in $16^{\circ}$ group, and 41.43 (9.33)${\mu}m$ in $26^{\circ}$ group. But there was no significant difference between groups. 2. The bond strength in Mean (S.D.) were ; 33.18 (5.53)kg in $6^{\circ}$ group, 23.47 (13.40)kg in $16^{\circ}$ group, and 19.75 (10.48)kg in $26^{\circ}$ group. $6^{\circ}$ group showed significantly higher value compared to $16^{\circ}$ and $26^{\circ}$ groups (p<0.05). Although the results of this study indicate $6^{\circ}$ divergency will be good for resin inlay, cavity preparation with this type will have lots of difficulties in manufacturing, try-in, and cementation procedures, such as deformation. So it is concluded that $16^{\circ}$ divergent cavity preparation is recommended in resin inlay technique.

• Elastomers and Composites
• /
• v.39 no.3
• /
• pp.179-185
• /
• 2004

Frequency dependency or electrical property stabilization during vulcanization of modified NR/IR composite materials was studied using in-situ electrical property measuring technique. Volume resistivity(p) before and after vulcanization reaction of the sample was measured as the function or frequency in the range or 1Hz to 10kHz at reaction temperatures of 130, 140, 150, and $160^{\circ}C$, respectively. A double stabilization mode of frequency dependency was observed, in which a slow stabilization process of p to a value of ca. $1.0{\times}10^7\;{\Omega}-cm$ occurred after a drastic initial decrease from ca. $9.0{\times}10^7\;{\Omega}-cm$. In addition, notable temperature dependencies of p values were also observed before and after vulcanization reaction, that is, p values at 130 and $140^{\circ}C$ after vulcanization were observed as about 1/3 of those values before vulcanization. All the observed facts were considered as the results from the interaction between the electrode and the bulk sample materials, i.e., electronic charge-discharge, and from the structure change of samples including CB rearrangement by the vulcanization.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.49 no.10
• /
• pp.841-847
• /
• 2021

In this paper, the applicability of the low-density surface film copper mesh for aircraft applications have been analyzed. Recently, low-density surface film copper mesh is developed to reduce weight and cost compared with traditional surface film copper mesh. In order to apply low-density surface film copper mesh to aircraft, it is needed to analyze its electromagnetic effects as well as structural integrity with sandwich panels to prevent pinholes. The structural integrity and electromagnetic characteristics have been analyzed for 2 samples of low-density surface film copper mesh and 1 sample of surface film copper mesh. To review the applicability of the low-density surface film, it is combined with sandwich composite panel to confirm pinhole effects. The low-density surface film has been modeled as a periodic structure and analyzed with 3D electromagnetic simulation tool. The simulation results has been verified through measured electromagnetic transmission results using free space measurements. From the results, it will be possible to use these results for the analysis and the applicability of low-density surface film copper mesh for aircraft.

• Korean Chemical Engineering Research
• /
• v.56 no.6
• /
• pp.819-825
• /
• 2018

Porous nanofibers comprising hollow ${\alpha}-Fe_2O_3$ nanospheres were prepared by applying both template method and Kirkendall diffusion effect to electrospinning process. During heat-treatment processes, the solid Fe nano-metals formed by initial heat-treatment in the carbon matrix were converted into the hollow structured ${\alpha}-Fe_2O_3$ nanospheres. In particular, PS nanobeads added in the spinning solution were decomposed and formed numerous channels in the composite, which served as a good pathway for Kirkendall diffusion gas. The resulting porous nanofibers comprising hollow ${\alpha}-Fe_2O_3$ nanospheres were applied as an anode material for lithium-ion batteries. The discharge capacities of the nanofibers for the 30th cycle at a high current density of $1.0A\;g^{-1}$ was $776mA\;h\;g^{-1}$. The good lithium ion storage property was attributed to the synergetic effects of the hollow ${\alpha}-Fe_2O_3$ nanospheres and the interstitial nanovoids between the nanospheres. The synthetic method proposed in this study could be applied to the preparation of porous nanofibers comprising hollow nanospheres with various composition for various applications, including energy storage.

• Journal of Advanced Navigation Technology
• /
• v.23 no.1
• /
• pp.84-89
• /
• 2019

This is a pilot study of machine learning based structural health monitoring system using flight data of composite aircraft. In this study, the most suitable machine learning algorithm for structural health monitoring was selected and dimensionality reduction method for application on the actual flight data was conducted. For these tasks, impact test on the cantilever beam with added mass, which is the simulation of damage in the aircraft wing structure was conducted and classification model for damage states (damage location and level) was trained. Through vibration test of cantilever beam with fiber bragg grating (FBG) sensor, data of normal and 12 damaged states were acquired, and the most suitable algorithm was selected through comparison between algorithms like tree, discriminant, support vector machine (SVM), kNN, ensemble. Besides, through neighborhood component analysis (NCA) feature selection, dimensionality reduction which is necessary to deal with high dimensional flight data was conducted. As a result, quadratic SVMs performed best with 98.7% for without NCA and 95.9% for with NCA. It is also shown that the application of NCA improved prediction speed, training time, and model memory.

• KEPCO Journal on Electric Power and Energy
• /
• v.5 no.3
• /
• pp.135-140
• /
• 2019

Lattice towers and tubular steel poles have been commonly used for electrical power transmission in Korea. They are durable, structurally stable, simple and can easily be constructed in limited spaces. However, residents are opposed to construct transmission lattice towers in their areas because they are not visually attractive, and electrical field occur at the transmission lines. Underground transmissions have been used instead of the traditional towers to resolve these problems, however they are not cost effective to construct and run. Therefore, we have developed eco-friendly towers that are more attractive, well blending into the surrounding environment, and much more economical than underground transmissions. There are four categories of the eco-friendly electric transmission towers about design aspects. Firstly, there is decoration type such as tree tower and ensemble tower. Tree tower looks like actual trees with leaves and branches so it blends into surroundings. Ensemble towers were designed after pair of crane birds. Those towers have decoration features and art works. Structural examination and manufacturing this type would be very similar to the conventional transmission towers. Secondly, there is arm design type such as traditional tower. Design features are added to the existing towers. As partial design can be adoptable on these types, it can easily meet height regulations and attach to conventional lattice towers and tubular steel poles. Also, these towers are more economical than others. Third category is multipurpose type such as Sail Tower. These towers have simple pole or tubular structure with features which can be used as information message board, public relations and much more. This type will face greater wind pressure because of the area of the board, also visibility must take into consideration. Lastly, there is moulding type such as arc pylon. It is different shape to the conventional towers - lattice towers and tubular steel poles. Dramatic design changes have been adapted - from a hard and static tower to a soft and curved tower. These towers will well stand out in the field. However, structural examination and manufacturing this type would be difficult and costly. Also certain towers of this type would require scaffolding or false work to construct, which will result in limitations of the construction area. This paper shows KEPCO 154 kV Sail tower in detail. KEPCO 154 kV Sail tower that is included in fabrication of sample tower and tower testing has developed and the results are presented in this paper. We hope that sail tower is also considered as a solution to have public acceptance or to create a familiar atmosphere among towers and people in coastal area.

• Applied Chemistry for Engineering
• /
• v.32 no.4
• /
• pp.361-370
• /
• 2021

Carbon fiber reinforced polymer (CFRP) is one of the composite materials, which has a unique property that is lightweight but strong. The CFRPs are widely used in various industries where their unique characteristics are required. In particular, electric and unmanned aerial vehicles critically need lightweight parts and bodies with sufficient mechanical strengths. Vehicles using the battery as a power source should simultaneously meet two requirements that the battery has to be safely protected. The vehicle should be light of increasing the mileage. The CFRP has considered as the one that satisfies the requirements and is widely used as battery housing and other vehicle parts. On the other hand, in the battery area, carbon fibers are intensively tested as battery components such as electrodes and/or current collectors. Furthermore, using carbon fibers as both structure reinforcements and battery components to build a structural battery is intensively investigated in Sweden and the USA. This mini-review encompasses recent research trends that cover the classification of structural batteries in terms of functionality of carbon fibers and issues and efforts in the battery and discusses the prospect of structural batteries.