C<SUB>f</SUB>/SiC 복합재료의 특성

조경서(Kyung Seo Cho),이현욱(Hyun Uk Lee),이상필,이진경(Jin Kyung Lee),변준형(Joon Hyung Byun) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

The mechanical properties of C<SUB>f</SUB>/SiC composite materials have been investigated in conjunction with a detailed analysis of microstructures. Polyvinylbutyral (PVB) resin was added into these materials when the pre-impregnated fabric structures were fabricated. The effect of PVB resin in the composites has been also examined. C<SUB>f</SUB>/SiC composites were fabricated at the temperature of 1820℃ by a liquid phase sintering (LPS) process using sintering additives of Al₂O₃, and Y₂O₃ particles. The ratio of additive compound (Al₂O₃/Y₂O₃) was fixed as 1.5. The volume fraction of carbon fiber were 15% and 20%, respectively The mass fraction of PVB resin was constant as 10%. The characterization of C<SUB>f</SUB>/SiC composties was investigated by means of SEM and three point bending test. C<SUB>f</SUB>/SiC composties without the addition of PVB resin showed definitely different fracture properties. C<SUB>f</SUB>/SiC composites represented an average strength of about 430 ㎫ at room temperature, accopanying the relative density of about 97%.

섬유강화 SiC<SUB>f</SUB>/SiC 복합재료의 기계적 특성

조경서(Kyung Seo Cho),이상필(Sang Pill Lee),이진경(Jin kyung Lee) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

This paper dealt with the mechanical properties of SiC<SUB>f</SUB>/SiC composite materials, in conjunction with detailed analysis of their microstructures. SiC<SUB>f</SUB>/SiC composites were fabricated by liquid phase sintering process(LPS) using a commercial SiC powder with an average size of about 0.3㎛. SiC<SUB>f</SUB>/SiC composites were sintered by a hot press process at 1820℃ under an applied pressure of 20 ㎫ for 1hr. The sintering additives was a complex mixture of Al₂O₃ and Y₂O₃ particles. The condition of sintering additives was selected as the constant composition ratio(Al₂O₃/Y₂0₃) of 1.5 and the total amount of 10wt%. Two-dimensional Tyranno SA fabrics with carbon coated layer were utilized as the reinforcing materials for ㎫ composites. The fiber preform for ㎫ composites were prepared by the infiltraion of complex mixture slurry with SiC, Al₂O₃ and Y₂O₃ powders into the fabric structure. The microstructure and mechanical properties were investigated by SEM and three point bending test at the room temperature.

보육시설 평가인증과정에 참여한 시설장과 교사의 인식에 관한 연구

조경서(Cho, Kyung Seo),유준호(Ryu, Jun Ho) 한국유아교육·보육복지학회 2009 유아교육·보육복지연구 Vol.13 No.1

연구에서는 평가인증을 통과한 보육시설의 시설장과 교사들이 평가인증에 대해 어떤 인식을 가지고 있으며, 평가인증 과정에서 경험한 어려움과 요구는 무엇인지, 평가인증 참여 후 경험한 변화는 무엇인지를 알아보고자 하였다. 본 연구에서는 성남시에 있는 보육시설 중 2006년과 2007에 평가인증에 통과한 시설을 대상으로 설문조사를 하였으며, 그 중 20곳의 보육시설을 직접 방문하여 심층면담을 실시하였다. 연구결과 평가인증제의 필요성에 대한 인식은 평가인증 참여 전보다 참여 후 더 높게 나타났다. 평가인증제의 유익성에 관하여는 교사의 전문성과 사명감 향상에 도움이 되고, 시설관리와 종사자 업무분장의 효율성을 높여준다고 인식하고 있었다. 평가인증 준비과정에서 가장 어려웠던 영역으로는 보육환경과 상호작용 영역을 들었으며 사후 평가인증이 자유의사라면 다시 평가를 받지 않거나 판단유보라는 응답이 많았다. 심층면담 결과, 평가인증 과정에서 시설장과 교사는 과중한 업무와 늦은 퇴근으로 인한 스트레스, 경제적인 부담, 학부모의 반대와 우려, 인증제에 대한 정보부족과 오류, 인력관리의 어려움, 조력의 혼란 등의 어려움을 겪는 것으로 나타났다. 요구 및 개선사항으로는 보육시설에 대한 인적‧물적 지원과 평가 및 조력방법의 개선, 평가인증제에 대한 적극적 홍보 등을 들었다. 평가인증 참여 후 경험한 긍정적인 변화로는 보육환경의 개선, 발달에 적합한 일과운영, 교수능력의 향상, 평가의 생활화와 동료장학의 필요성 인식 등이고, 반면 직업에 대한 회의, 이직의 증가, 가시(可視)적인 것에 대한 추구 등이 부정적인 변화인 것으로 나타났다. The purpose of the study was to research on experiences and perceptions of directors and teachers at child care centers participating in the Korean child care center accreditation process during the year of 2006 and 2007 in Sung Nam. Questionnaire distributed 186 child centers and conducted In-depth interview at 20 child care centers. The results of the study can be summarized as follows:First, the perception of the need to Korean child care centers accreditation increased after Accreditation. And Expertises and sense of duties, efficient managements were improved. Directors and teachers at child care centers felt ill at ease making a good child care center environment, child-teacher interaction. Second, heavy affairs and late leaving put directors and teachers under a lot of stress. And because of the cost burden, lack of information, miscarrying nurture affairs, confusion of assistance, they had a hard time. Directors and teachers demanded personnel economic support, improvement of evaluating system, active public relations about the Korean child center accreditation. Third, after child care center accreditation, they experienced positive changes and negative changes. Positive changes were improvement of child care center environment, specificity and making a good child care center environment, developmentally appropriate daily management programs, improvement of teaching competency. Negative changes were skepticism about their occupation, increasing separation rates, attaching great weight on evidences only.

SiC 재료와 SiC<SUB>f</SUB>/SiC 복합재료의 특성

조경서(Kyung-Seo Cho),이상필(Sang-Pill Lee),이진경(Jin-Kyung Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

The mechanical properties of monolithic SiC and SiC<SUB>f</SUB>/SiC composite materials has been investigated, based on the detailed analysis of their microstructures. Especially, the characterization of SiC<SUB>f</SUB>/SiC composite materials were examined at the elevated temperatures in the argon atmosphere. SiC based materials were fabricated by a liquid phase sintering process (LPS), using a commercial SiC powder with an average size of about 0.3㎛. Two-dimensional Tyranno SA fibers were utilized as a reinforcing material for SiC<SUB>f</SUB>/SiC composite. LPS-SiC based materials were fabricated at the temperature of 1820℃ using the additive compound of Al₂O₃, and Y₂O₃ particles. The compositional ratios of additive materials (Al₂O₃/Y₂O₃) for LPS-SiC materials were changed from 0.4 to 1.5. LPS-SiC materials represented' the good density of about 3.2 Mg/㎥ and an average flexural strength of about 810 ㎫ at the additive composition ratio of 1.5. The sintering density of LPS-SiC<SUB>f</SUB>/SiC was also similar to that of LPS-SiC materials. However, the flexural strength of LPS-SiC<SUB>f</SUB>/SiC composites greatly decreased with the increase of test temperature.

압력/진공 릴리프 밸브 스테인레스 강의 내열특성

조경서(Kyung-Seo Cho),이상필(Sang-pill Lee),이진경(Jin-Kyung Lee),이향준(Hyang-Jun Lee),이민원(Min-Won Lee),기동환(Dong-Hwan Ki) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

The present work dealt with the high temperature properties of STS 316 steels for disk or sheet materials, in order to develop the safe relief valve of oil or gas storage tank. Especially, the critical temperature difference for the strength degradation of STS 316 steels has been investigated by the high temperature thermal shock test. The flexural strength of stainless 316 steels gradually increased with the increase of thermal shock temperature, accompanying the rapid reduction at the thermal shock temperature higher than 973 K. Especially, the stainless 316 steels represented an average flexural strength of about 540 ㎫ at the thermal shock temperature of 1273 K, corresponding to about 85 % of as-received materials.

액상소결 SiC 재료의 특성 평가

조경서(Kyung-Seo Cho),이문희(Moon-Hee Lee),이상필(Sang-Pill Lee),이진경(Jin-Kyung Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

The mechanical and microstructure properties of liquid phase sintered (LPS) SiC materials have been investigated, in conjunction with a nondestructive technique by the ultrasonic wave. The thermal shock damage behaviors of LPS-SiC materials were also examined. LPS-SiC materials were fabricated at the temperature of 1820 ℃ using the additives of Al₂O₃, and Y₂O₃ particles. The compositional ratios of additive materials (Al₂O₃/Y₂O₃) for LPS-SiC materials were changed from 0.4 to 1.5. LPS-SiC materials represented the good density of about 3.2 Mg/㎥ and an average flexural strength of about 725 ㎫ at an additive composition ratio of 1.5. The attenuation coefficient related to the velocity of ultrasonic wave was greatly changed by different additive composition ratios of LPS-SiC materials. The flexural strength for LPS-SiC materials increased with the decrease of attenuation coefficient. In accordance with the increase of thermal shock cycle, the attenuation coefficient of LPS-SiC materials also increased, due to the creation of microcracks.

C/SiC 복합재료의 제조공정에 관한 연구

이진경(Jin Kyung Lee),이상필(Sang Pill Lee),조경서(Kyung Seo Cho),변준형(Joon Hyung Byun) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.4

한국 보육정책 협력네트워크의 발전적 구축에 관한 연구

이재무(Lee, Jae-Moo),조경서(Cho, Kyung-Seo),송영선(Song, Young-Sun) 한국영유아보육학회 2012 한국영유아보육학 Vol.0 No.73

본 연구는 민관 각 부문의 실효성 높은 보육체제 마련과 보육정책 집행의 효과성 증진에 일익을 제공하고자 협력네트워크 개념을 준용하여 수행되었다. 분석을 위해 중앙정부와 지방정부, 보육시설, 학부모?영유아를 중요 정책행위자로 규정하고 그들 간의 완전히 대등한 연계와 협력지향의 상호작용, 네트워크 내 중재자로서 중앙정부의 원활한 조정 활동을 바람직한 협력네트워크 구조로 설정하였다. 이렇게 설정된 분석기준에 준하여 분석한 결과, 현재 중앙정부와 학부모?영유아 그리고 학부모?영유아와 보육시설 사이는 적절한 협력관계를 갖추고 있었지만 지방정부와 보육시설 간 관계는 대대적인 개선을 요하는 상태였다. 또한 중앙정부의 네트워크 내 조정 기능 수행 수준도 미흡한 상태이기 때문에 그에 대한 보강이 필요함을 제언하였다. The purpose of study is to increase the effectiveness of the Child Care-Education Policy by suggesting the ideal private-public cooperation model with the network system to analyze the relationship between the committees and beneficiaries of the Child Care-Education Policy in Korea. Therefore, an adequate collaborative network system was organized as follows. The Central Government, Local Governments, nursery facilities, parents and children were stipulated as the essential elements of the network system ?. and their collaboratively equivalent interactions with the administrator’s ability to arbitrate the Central Government were established Analyzing based on the model and the actual cases, the "Central Government ?Parents ?Children" network system and the "Parents ?Children ?Nursery Facilities" network system were appropriately maintained, whereas, the relationship between the Local Governments and the nursery facilities required some improvement. Moreover, the Central Government’s network system has revealed insufficient maintenance and management skills, thus, a strong need of reinforcement was proposed.

액상소결 SiCf/SiC 복합재료의 미세조직 및 강도특성

이문희(Moon Hee Lee),조경서(Kyung Seo Cho),이상필(Sang Pill Lee),이진경(Jin Kyung Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

The efficiency of fiber reinforced CMC(ceramic matrix composite) on the SiC materials have been investigated, in conjunction with the fabrication process by liquid phase sintering and the characterization. LPS-SiC<SUB>f</SUB>/SiC composites was studied with the detailed analysis such as the microstructure, sintered density, flexural strength and fracture behavior. The applicability of carbon interfacial layer has been also investigated in the LPS process. Submicron SiC powder with the constant total amount and composition ratio of Al₂O₃, Y₂O₃ as sintering additives was used in order to promote the performance of the SiC matrix material. LPS-SiC<SUB>f</SUB>/SiC composites were fabricated with hot press under the sintering temperature and applied pressure of 1820℃ and 20㎫ for 1hr. The typical property of monolithic LPS-SiC materials was compared with LPS-SiC<SUB>f</SUB>/SiC composites.

C<SUB>f</SUB>/SiC 복합재료의 액상소결 및 특성

이현욱(Hyun-Uk Lee),조경서(Kyung-Seo Cho),이상필(Sang-Pill Lee),이진경(Jin-Kyung Lee),손인수(In-Soo Son),변준형(Joon-Hyung Byun) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.4

Both microstructure and mechanical properties of C<SUB>f</SUB>/SiC composites were examined in this study. C<SUB>f</SUB>/SiC composites were fabricated by a liquid sintering process(LPS), using a commercial SiC powder with an average size of about 0.3 ㎛. C<SUB>f</SUB>/SiC composites were sintered at the temperature of 1820 ℃ under the applied pressure of 20 ㎫ for the pressure holding time of 1 hour. The sintering additives for the fabrication of LPS-C<SUB>f</SUB>/SiC composites were selected as a compound of Al₂O₃ and Y₂O₃ particles. The composition ratio(Al₂O ₃/Y₂O₃) of additive material and its total amount were 1.5 and 10 wt.%, respectively. Plain woven carbon fabrics were treated by a sizing process, prior to the preparation of fiber preform for the fabrication of LPS-C<SUB>f</SUB>/SiC composites. The fiber preforms were prepared by the infiltration of complex mixture slurry with SiC, Al₂O₃, Y₂O₃ powders and polyvinylbutyral(PVB) resin into the fabric structure.