• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.230-237
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• 2012

The ultrasonic resonance method was applied to detect the disbond interface and empty layer between steel and FRP of the exit cone. The ultrasonic resonance method can easily detect the disbond interface and empty layer by amplifying the ultrasonic signal, but pulse echo method is difficult to distinguish adhesive interface from disbond interface or empty layer. The resonance frequency was predicted using the pressure reflection coefficient of 3-layered medium, and measured from ultrasonic signal of the test block using Fast Fourier Transform. The ultrasonic resonance proved that the predicted resonance frequency was in good agreement with the measured resonance frequency.

• Journal of Korea Foundry Society
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• v.42 no.4
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• pp.209-217
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• 2022

In the present study, in order to prevent the misrun defects that occur during traditional brass casting, a method for selecting the proper casting process conditions is proposed. A learning model was developed and demonstrated to be able to learn the presence or absence of defects according to the casting process conditions and to predict the occurrence of defects depending on the certain process given. Appropriate process conditions were determined by applying the proposed method, and the determined conditions were verified through a comparison of different simulation results with additional conditions. With this method, it is possible to determine the casting process conditions that will prevent defects in the desired sand model. This technology is expected to contribute to realization of smart traditional brass farming workshops.

• Journal of the Korea Organic Resources Recycling Association
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• v.8 no.3
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• pp.124-130
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• 2000

This study was conducted to evaluate effects of gas retention time and filling depth of a compost-based biofilter on removal of vapor phase gasoline and to suggest operational improving method. Gas empty bed retention times(EBRTs) were 4, 10, and 20 minutes, respectively. EBRT of over 10 minutes was required in both cases of TPH(total petroleum hydrocarbons) and BTEK (bezene, toluene, ethylbenzene, and xylene). Filling depths were 25, 50, 75, and 100cm, respectively. To treat gasoline TPH effectively, controlling other operational parameters including EBRT and gas loading rate was more important than increasing filling depth simply. 1m filling depth was sufficient in treating BTEX without controlling other operational parameters greatly.

• Journal of Adhesion and Interface
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• v.22 no.3
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• pp.106-110
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• 2021

Recently, research using waste among eco-friendly materials has been attracting attention. In this study, we investigated the physical properties of blends in which high density polyethylene (HDPE) was filled with waste gypsum (CaSO₄) generated during fertilizer manufacturing. Composites were prepared by adding the gypsum content 0~20 wt% using a twin screw extruder. The mechanical, rheological, and thermal properties of the composites were evaluated. It was found that the tensile strength of the composites was less than 4.1% compared to that of unfilled HDPE, so there is no significant deterioration in physical properties. The thermal stability of the composites was improved as the gypsum content increased and the gypsum content had little effect on the viscosities of the composites.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2016.11a
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• pp.275-277
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• 2016

본 논문에서는 Door Fan Test 수행 사례를 중심으로 사전 준비에 필요한 사항에 대해 분석하였다. 분석 결과 관통부 주위 개구부, 벽체 틈새 개구부 등 방화구역의 누설부위를 통해 약제가 누출되는 문제가 있었다. 원인으로는 전기배선 공사로 인해 내화충전된 부분을 제거하고 공사 후 다시 충전하지 않는 경우, 벽과 천장사이의 틈을 내화 실란트 등으로 마감을 하지 않은 경우가 대부분이었다. 이와 같이 누설부위가 많은 경우 테스트의 결과 불합격이 나오게 되며, 이러한 문제점을 개선하기 위해 사전현장조사를 통해 방호구역의 누설부위를 조사하고 보완조치를 진행한 후 테스트를 수행하는 절차가 필요하였다. 한편, 테스트 운영에 관한 사항으로는 해당 실(room)을 위한 충분한 유량 미확보, 장애물로 인한 와류형성, 차압측정구의 설치문제 등이 있었다. 이를 개선하기 위해서 공기를 유입하는 실은 외부로부터 충분한 공기유입이 있어야하며, 팬 앞의 장애물을 제거하거나 팬의 설치 위치를 조정하는 것이 필요하며, 공기의 유동이 가장 적은 곳에 측정구를 설치하는 등의 조치가 필요하다.

• Restorative Dentistry and Endodontics
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• v.31 no.4
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• pp.323-329
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• 2006

The aim of this study was to evaluate the retrievability of Resilon as a root canal filling material Twenty-seven human single-rooted extracted teeth were instrumented utilizing a crown down technique with Gates-Glidden burs and ProFile system. In group1 (n = 12) canals were obturated with gutta percha and AH-26 plus sealer using a continuous wave technique and backfilled. In group 2 (n = 15) Resilon was used as a filling material. Then teeth were sealed and kept in $37^{\circ}C$ and 100% humidity for 7 days. For retreatment, the samples were re-accessed and filling material was removed using Gates-Glidden burs and ProFiles. Teeth were sectioned longitudinally to compare the general cleanliness and amount of debris $({\times}\;75)$ using SEM. Chi-square test was used $({\alpha}\;=\;0.05)$ to analyze the data. The total time required for removal of filling materials was expressed as mean ${\pm}SD$ (min) and analyzed by the Student t-test $({\alpha}\;=\;0.05)$, Required time for retreatment was $3.25\;{\pm}\;0.32$ minutes for gutta percha/ AH 26 plus sealer and $3.05\;{\pm}\;0.34$ minutes for Resilon. There was no statistically significant difference between the two experimental groups. There was no significant difference between the groups in the cleanliness of the root canal wall. This study showed that Resilon was effectively removed by Gates-Glidden burs and ProFiles.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.46-53
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• 2004

Ultrasonic testing method has been developed to evaluate flaw of adhesive layers in blast tube for the reliability of the rocket nozzle. The ultrasonic reflection from the interface between the steel sheet and the epoxy adhesive is measured with a high-frequency Pulse-echo setup in order to identify contact debonding and missing adhesive in epoxy layer between steel and FRP layers. The steel sheet is resonated by low-frequency ultrasound, and the gap size underneath the measuring location is estimated from the resonance responses. For practical application in industry an automated testing system has been developed where the proposed approach is implemented. The performance of the proposed approach has been verified by actual measurement of gap sizes from the cross-sections of cut specimens using an optical microscope.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.186-192
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• 1999

Dang-Chin feldspar powder with the mean particle size of 9.1 $\mu\textrm{m}$ was added to the synthesized mullite powder with the particle size of +325∼-200 mesh and the powder compact was prepared by PLPP(pressureless powder packing method). Densification behaviors were observed in sintering temperature range of 1200∼1400$^{\circ}C$. The binder solution of 4% PVA was infilterated into packed powder to the suitable strength. The PLPP method makes it possible to form compacts without clay as plasticizer. Therfore there was no defect caused by phase transition after sintering. Additionally, we observed the dense microstructure by the melting of feldspar. When the mullite compacts with feldspar of 30% were sintered at 1300$^{\circ}C$-4 hrs, we obtained the dense microstructure with zero water absorption and porosity <1%. When these compacts were sintered longer than 4 hrs at 1300$^{\circ}C$ or higher than 1400$^{\circ}C$, the examggerated grain growth of mullite was observed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.230-237
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• 2003

Ultrasonic testing method has been developed to evaluate adhesive layers in blast tube for the reliability of the rocket. The main objective of the present work was to find debonding and missing adhesive in epoxy layer between steel and FRP layers. In this approach, the ultrasonic reflection from the interface between the steel sheet and the epoxy adhesive is measured with a high-frequency pulse-echo setup in order to identify contact debonding and missing adhesive. Then, the steel sheet is excited to resonance by low-frequency ultrasound, and the gap size underneath the measuring location is estimated from the resonance responses. For practical application in industry an automated testing system has been developed where the proposed approach is implemented. The performance of the proposed approach has been verified by actual measurement of gap sizes from the cross-sections of cut specimens using an optical microscope.

• Proceedings of the KAIS Fall Conference
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• 2011.12b
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• pp.514-517
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• 2011

본 연구에서는 사각형태 화장품 케이스 사출성형 시 발생되었던 수지 미성형 불량을 해결하기 위하여 사출성형해석 기술을 통해 성형품 형상변경 및 사출금형 내 유동 시스템 수정방안 도출을 수행하였다. 대상제품인 사각형태 화장품 케이스는 상측부 케이스로서 케이스 외관에 게이트 및 취출흔적이 남지 않아야 함에 따라 측면부 게이트 적용으로 유동거리가 길어져 미성형 불량이 다수 발생하는 제품이다. 따라서, 수지 유동성 향상과 더불어 효율적인 보압전달을 통하여 수지 충전 및 변형발생 저감을 위하여 성형품 형상변화 및 유동시스템 변화에 따른 사출성형해석을 수행하고 결과를 고찰하였다. 이로써 최종적으로 수지 미충전으로 인한 미성형 불량을 제거하고 성형품 변형을 줄일 수 있는 수지유동시스템 수정방안을 제시하였다.