• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2001.11a
• /
• pp.90-93
• /
• 2001

In the present work, ultrasonic testing method has been developed to evaluate adhesive layers in rocket motor case assembly for the reliability of the rocket. The main objective of the present work was to find debonding between steel and rubber layers. The relationship between adhesion ratio and reflected ultrasonic amplitude was calculated by considering reflection coefficient at the interface between steel and rubber layers. It was found that the higher amplitude of ultrasound is reflected for the debonding area, and shown good agreements with experimental results. The ultrasonic C-scan images offers good implements for the determination of debonding area. The nondestructive testing results were compared with the micrography of destruective testing. As results, ultrasonic testing could be utilized for the evaluation of adhesive layer in the rocket motor case assembly.

• Transactions of Materials Processing
• /
• v.12 no.4
• /
• pp.370-375
• /
• 2003

Determination of the interface heat transfer coefficient was investigated in non-isothermal bulk forming of glass-coated Ti-6Al-4V. FE analysis and experiments were conducted. Equipment consisting of AISI Hl3 die was instrumented with thermocouples located at sub-surface of the bottom die. Die temperature changes were investigated in related to the process variables such as reduction, lubricant and initial die temperature. The calibration approach based on heat conduction and FE analysis using an inverse algorithm were used to evaluate the interface heat transfer between graphite-lubricated die and glass-coated workpiece. The coefficients determined were affected mainly by the contact pressure. The validation of the coefficients was made by the comparison between experimental data and FE analysis results.

• Korean Journal of Materials Research
• /
• v.6 no.6
• /
• pp.610-617
• /
• 1996

강유전체 재료의 하부전극으로 사용되고 있는 Pt/Ti 박막의 접착력에 대한 열처리 분위기의 영향을 연구하였다. 시편의 접착력은 90$^{\circ}$ 필 테스트 방법을 사용하여 정량적으로 측정하였다. 열처리 후 사용된 분이기에 관계없이 모두 접착력이 감소하였는데 특히 산소분위기에서 열처리 한 시편의 접착력이 매우 크게 감소하였다. AES depth profile과 단면 TEM을 이용하여 계면반응을 관찰한 결과 산소열처리시에는 Ti가 외부에서 확산해 온 산소와 반응하여 rutile TiO2상이 형성됨을 알 수 있었다. 그러므로 산소열처리 후에 일어나는 접착력의 급격한 감소 원인은 열처리시 취약한 TiO2상이 형성되며 이로 인해 Ti 접착층이 고갈되기 때문임을 알 수 있었다.

• Proceedings of the KIEE Conference
• /
• 2002.11a
• /
• pp.124-126
• /
• 2002

In this study, composite materials were put to dry interfacial treatment by use of plasma technology. It has been presented that the optimum parameters for the best wettability of the samples at the time of generation of plasma were oxygen atmosphere, 0.1 torr of system pressure, 100 W of discharge power, and 3 minutes of discharge time. Also, the surface resistance rate, dielectric property and tensile strength were improved.

• Journal of Adhesion and Interface
• /
• v.10 no.3
• /
• pp.117-126
• /
• 2009

Epoxy/anhydride systems with silica filler were studied to improve the cure behavior and characteristics. To study the curing process of epoxy/anhydride using DSC and a stress rheometer, it was observed that gelation temperature increased by increasing the thermal rate or in high isothermal conditions, while it was observed that the degree of cure at gelation decreased. Thermal stability of the epoxy/anhydride system showed any increment by increasing silica contents, except slight decrease of weight by containing humidity. The epoxy resin cured with 30% of silica filler decreased coefficient thermal expansion (CTE) about 33% to show $40ppm/^{\circ}C$. Specimens filled with 30 wt% of silica showed 60% increase in storage modulus at $30^{\circ}C$ to show 3909 MPa compared with neat resin to 2,377 MPa. Epoxy/anhydride systems with surface treated silica by silane coupling agent decreased storage modulus.

• Applied Chemistry for Engineering
• /
• v.8 no.5
• /
• pp.715-721
• /
• 1997

W/O/W multiple emulsions were prepared comprising $MgSO_4$ in the inner aqueous phase as a model drug. The stability and drug release behavior of the multiple emulsions were studied using optical microscopy, viscometry and conductometry. Glucose was introduced in the outer aqueous phase to reduce the osmotic pressure gradient across the oil layer arising from the localization of drug molecules in the inner water phase. It was found that the presence of glucose was effective in stabilization of the multiple emulsions and in control of the release rate of drug more evidently when oil phase was partially hydrophilized with cetostearyl alcohol. This may be attributed to the fact that the migration of water accompanying the hydrophilic surfactant to the inner water phase was limited under a reduced osmotic pressure gradient and thereby slow down the destabilization of the oil/inner water interface.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.5
• /
• pp.545-551
• /
• 2012

We investigated the diffusive transport of bupivacaine HCl through the microchannels of microfluidic drug delivery devices. In the biodegradable microfluidic drug delivery devices developed in this research, the drug release rate can be controlled by simply modulating the geometrical parameters of the microchannels, such as the length, number, and cross-sectional area of the microchannels, when the microchannels are used as paths for drug release. However, the hydrophobic nature of a biodegradable polymer, 85/15 poly(lactic-co-glycolic acid), hinders the infiltration of a release medium (phosphate-buffered saline) through the microchannels into the reservoir of a device that contains bupivacaine HCl, at the early stage of drug release. This can have an adverse effect on the early stage release of local analgesic compounds from the device. In this study, microfluidic channels were surface-treated with surfactants such as PEG600 and Tween80, and the effects of the surfactants on the release performance are presented and analyzed.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.27 no.2
• /
• pp.252-258
• /
• 1998

The strain producing biosurfactant was isolated from soil smples. The isolated strain was identified as the genus Nocardia through its morphological, cultural and physiolgical characteristics. A high concentration of the biosurfactant by Nocardia sp. L-417 was obtained after 4 days of cultivation in the culture medium containing 3% n-hexadecane, 0.1% $NaNO_3$, 0.02% $K_2HOP_4$, 0.01% $H_2PO_4$, 0.01% $MgSO_4$.$7H_2O$, 0.01% $CaCl_2$, 0.02% yeast extract, and 0.02% tryptone. The optimum pH and temperature for biosurfactant production were pH 6.0 and $30^{\circ}C$, respectively. Furthermore, most biosurfactans were produced during the exponential growth phase, and this fact indicated that the biosurfactans production was growth-associated. The biosurfactant showed the good emulsification activities on various emulsifying substrates such as bunker A, paraffin, corn oil which are used widely in industries.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2001.10a
• /
• pp.724-728
• /
• 2001

In this study, the dielectric breakdown of epoxy composites used for transformers was experimented and then its data were simulated by Weibull distribution probability. The dielectric breakdown characteristics origin in epoxy composites were examined and various effects of dielectric breakdown on epoxy composites were also discussed. As a result, first of all, speaking of dielectric breakdown properties, the more hardener increased the stronger breakdown strength at low temperature because of cross-linked density by the virtue of ester radical. And the breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised, the electric field is concentrated, and the acceleration of electron and the growth of electron avalanche are early accomplished. In the case of filled specimens with treating silane, the breakdown strength become much higher since this suggests that silane coupling agent improves interfacial combination and relaxs electric field concentration. Finally, from the analysis of weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1%, the applied field value needed to be under 21.5㎹/cm.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2002.11a
• /
• pp.779-783
• /
• 2002

The dielectric breakdown of epoxy composites used for transformers was experimented and then its data were simulated by Weibull distribution probability. As a result, first of all, speaking of dielectric breakdown properties, the more hardener increased the stronger breakdown strength at low temperature because of cross-linked density by the virtue of ester radical. And the breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised, the electric field is concentrated, and the acceleration of electron and the growth of electron avalanche are early accomplished. In the case of filled specimens with treating silane, the breakdown strength become much higher since this suggests that silane coupling agent improves interfacial combination and relaxs electric field concentration. Finally, from the analysis of weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1%, the applied field value needed to be under 21.5MVcm.