• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.118-121
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• 2002

Polyvinylidene di-fluoride (PVDF) film sensor appeared to be practically useful for the structural health monitoring of composite materials and structures. PVDF film sensors were either attached to or embedded in the graphite/epoxy composite (CFRP) samples to detect the fatigue damage at the bondline of single-lap joints or the tensile failure of unidirectional laminates. PVDF sensors were sensitive enough to detect and determine the crack front in linear location since composites usually produce very energetic acoustic emission (AE). PVDF sensors are extremely cost-effective, as flexible as other plastic films, in low profile as thin as a few tens of microns, and have relatively wide-band response, all of which characteristics are readily utilized for the structural health monitoring of composite structures. Signals due to fatigue damage showed a characteristics of mode II (shear) type failure whereas those from fiber breakage at DEN notches showed that of mode I (tensile) type fracture.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.455-459
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• 2017

The development of flexible transparent electrode has been paid attention for flexible electronics. In this study, we have developed transparent electrode based on silver nanowires with improved electrical property and stability through ion-beam treatment. The energetic particles of ion-beam could sinter junctions of each silver nanowires and etch out polyvinylpyrollidone(PVP) coated on silver nanowires. The sheet resistance of silver nanowire transparent electrode was reduced by 74%, and the resistance uniformity was increased about 3 times after exposure of ion beam. Moreover, the stability at $85^{\circ}C$ of temperature and 85% of relative humidity could be also improved.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.152-153
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• 2006

We demonstrate the methodology of engineering the multi-component ceramic nanopowder with precise morphology by nanoblast calcinations decomposition of preliminary engineered nanoreactors. Multiple explosions of just melted $C_3H_6N_6O_6$ embedded into preliminary engineered nanoreactors break apart the agglomerates due to the highly energetic impacts of the blast waves. Also, the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during each nano-explosion in surrounding area. This methodology was applied for production of agglomeratefree nano-aggregates of $Gd_{20}Ce_{80}O_{1.95}$ with an average size of 42 nm and $LaSrGaMgO_{3-x}$ nanopowder with an average aggregate size of 83 nm.

• Advances in aircraft and spacecraft science
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• v.9 no.2
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• pp.149-167
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• 2022

A Modified fuzzy mechanical control of large-scale multiple time delayed dynamic systems in states is considered in this paper. To do this, at the first level, a two-step strategy is proposed to divide a large system into several interconnected subsystems. And we focus on the damage propagation for aircraft structural analysis of composite materials. As a modified fuzzy control command, the next was received as feedback theory based on the energetic function and the LMI optimal stability criteria which allow researchers to solve this problem and have the whole system in asymptotically stability. And we focus on the results which shows the high effective by the proposed theory utilized for damage propagation for aircraft structural analysis of composite materials.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.3
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• pp.418-424
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• 2015

The chemical response of energetic materials is analyzed in terms of 1) the thermal decomposition under the thermal stimulus and 2) the reactive flow upon the mechanical impact, both of which give rise to an exothermic thermal runaway or an explosion. The present study aims at building a set of chemical kinetics that can precisely model both thermal and impact initiation of a heavily aluminized cyclotrimethylene-trinitramine (RDX) which contains 35% of aluminum. For a thermal decomposition model, the differential scanning calorimetry (DSC) measurement is used together with the Friedman isoconversional method for defining the frequency factor and activation energy in the form of Arrhenius rate law that are extracted from the evolution of product mass fraction. As for modelling the impact response, a series of unconfined rate stick data are used to construct the size effect curve which represents the relationship between detonation velocity and inverse radius of the sample. For validation of the modeled results, a cook-off test and a pressure chamber test are used to compare the predicted chemical response of the aluminized RDX that is either thermally or mechanically loaded.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.46-55
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• 2016

The kinetic analysis of a heavily aluminized cyclotrimethylene-trinitramine(RDX) is conducted using differential scanning calorimetry(DSC), and the Friedman isoconversional method is applied to the DSC experimental data. The pre-exponential factor and activation energy are extracted as a function of the product mass fraction. The extracted kinetic scheme does not assume multiple chemical steps to describe the complex response of energetic materials; instead, a set of multiple Arrhenius factors is constructed based on the local progress of the exothermic reaction. The resulting reaction kinetic scheme is applied to two thermal decomposition tests for validating the reactive flow response of a heavily aluminized RDX. The results support applicability of the present model to practical thermal explosion systems.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.58-63
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• 2020

THPP is a type of metallic complex explosive used in initiators, consisting of TiH₂ and KClO₄. In this case KClO₄ includes ClO₄^- which is a harmful substance that may cause thyroid dysfunction or tumors. In this study KIO₄ is applied to a new type of environmentally friendly explosive as a substitute to the conventional KClO₄. Tests were carried out to see if KIO₄ can be made a successful replacement for KClO₄.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.84-91
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• 2021

Effervescent tablets generate gas bubbles when chemical reaction occurs between water and tablets. Most of previous studies have been focused on pharmaceutical characteristics of tablets. However, for their applications in disinfectants, cleaners, and pesticides, physical characteristics of bubbles released from the effervescent tablets when they are in water are important. In this study, we experimentally investigated the characteristics of microbubbles generated by an effervescent tablet made of sodium bicarbonate and tartaric acid using PDPA and high-speed camera. Microbubbles were generated using different weights of effervescent tablet as well as in different water temperature. The experimental study shows increase in reaction time, bubble concentration and rise velocity as the weight of effervescent tablet increases from 1 to 20 g. The decrease in average bubble diameter was observed when the temperature of water increased from 25 to 45 ℃. Further, reaction time varies inversely with increase in water temperature, while bubble rise velocity is directly proportional to increase in water temperature. Effervescent table continuously generates the bubble with approximately constant diameter (235 ㎛) in the water. However, bubble concentration and bubble rise velocity decreased over time.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.334-341
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• 2011

The mechanism behind super-filling of high-aspect-ratio features with Cu by catalyst-enhanced chemical vapor deposition (CECVD) coupled with plasma treatment is described and the metrology required to predict the filling feasibility is identified and quantified. The reaction probability of a Cu precursor was determined as a function of substrate temperature. Iodine adatoms are deactivated by the bombardment of energetic particles and also by the overdeposition of sputtered Cu atoms during the plasma treatment. The degree of deactivation of adsorbed iodine was experimentally quantified. The quantified factors, reaction probability and degree of deactivation of iodine were introduced to the simulation for the prediction of the trench filling aspect by CECVD coupled with plasma treatment. Simulated results show excellent agreement with the experimental filling aspects.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.895-901
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• 2023

Oxide-dispersion- strengthened nickel alloys with Hf additions are expected to present high temperature mechanical properties and durable helium resistance based on first-principles density functional theory (DFT) calculations. Energetic and charge density evaluations of the helium behaviors were performed in Ni matrix, Y₂Hf₂O₇ oxide and the oxide/matrix interface. With the presence of coherent Y₂Hf₂O₇ in Ni matrix, chances of helium bubbles in Ni can be greatly diminished. The helium atoms shall occupy the interfacial site initially, then diffuse into in the octahedral sites of Y₂Hf₂O₇, and these oxide-captured He atoms prefer to separate individually. Much higher diffusion barrier of He in Y₂Hf₂O₇ than in nickel is related to the strong hybridization between interstitial He-1s and nearest-neighboring O-2p orbitals.