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.

유아의 걱정에 관한 연구

조경서(Kyung Seu Cho) 한국영유아교원교육학회 1998 幼兒 敎育學論集 Vol.2 No.1

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.

어머니의 스마트폰 의존성이 유아의 문제행동에 미치는 영향

조경서(Kyung Seu Cho),김은주(Eun Joo Kim) 한국아동복지학회 2016 한국아동복지학 Vol.- No.53

본 연구는 유아의 스마트폰 의존성을 매개로 어머니의 스마트폰 의존성이 유아의 문제행동에 미치는 직, 간접효과를 알아보기 위한 것이다. 이를 위해 서울과 경기지역의 2∼6세 유아기 자녀를 둔 어머니 300명을 대상으로 설문조사를 실시하였다. 연구모형은 유아의 스마트폰 의존성을 매개로 어머니의 스마트폰 의존성이 유아 문제행동에 영향을 미치는 경로를 분석하는것이다. 연구결과 어머니의 스마트폰 의존성은 유아의 스마트폰 의존성과 문제행동에 직접적인 영향이 있는 것으로 나타났고, 그중에서도 유아의 문제행동에 미치는 직접효과가 더 큰 것으로 나타났다. 또한 어머니의 스마트폰 의존성은 유아 스마트폰 의존성을 매개로 유아 문제행동에 간접효과가 있는 것으로 나타났다. 본 연구결과는 유아와 부모의 스마트폰 사용에 대한교육적 접근의 필요함과, 유아의 문제행동에 있어서 주 양육자인 어머니의 올바른 스마트폰 사용에 대한 인식과 조절, 예방프로그램 개발의 필요성을 시사하고 있다. The purpose of this study was to examine the relationship between mothers’ smartphone dependency(MSD) and their children’s problem behavior and how children’s smartphone dependency(CSD) mediates this relationship. A survey was conducted in the Seoul and Gyeonggi of 300 mothers having children from two to six years old. The results showed that MSD was directly related to both CSD and children’s problem behavior, and in particular, had greater effects than CSD on children’s problem behavior. CSD was found to mediate the relationship between MSD and children’s problem behavior. The results suggest that mothers and their children should be provided with education on the proper usage of smartphone to prevent problem behavior in children, and that the development of preventive programs for smartphone addiction is needed.

유아의 걱정에 관한 연구

조경서(Kyung Seu Cho) 한국영유아교원교육학회 1997 幼兒 敎育學論集 Vol.1 No.1

제방의 취약구간 파악을 위한 전기비저항과 탄성파속도의 교차출력 해석

조경서 ( Kyoung-seo Cho ),김정인 ( Jeong-in Kim ),김종우 ( Jong-woo Kim ),김지수 ( Ji-soo Kim ) 대한지질공학회 2021 지질공학 Vol.31 No.4

각 탐사의 반응 값은 지하 매질의 특정 물성에 따라 달라지기 때문에 한가지의 지구물리학적 방법만으로는 탐사목적을 달성하지 못하는 경우가 종종 있다. 특히 지질재해 위험에 취약한 지역을 조사하는 경우, 인명 및 재산피해를 최대한 줄이기 위해 한 가지 이상의 탐사방법을 사용하는 것이 효과적이다. 제방의 안전성 평가를 위한 이 연구에서는 각 탐사결과들을 개별적으로 해석하는 대신 탄성파속도(굴절법에 의한 P파속도와 MASW의 S파속도)와 전기비저항 값들을 통계적으로 분석하여 결정된 임계값들을 기반으로 취약구간과 안전구간 등으로 구분하는 사분면 상관기법을 수행하였다. 임계값은 수평 4층 구조와 경사진 파쇄대에 대한 모델자료를 가지고 수행한 사분면 상관기법을 테스트하는 과정에서 두 개의 속성자료 모두 평균에서 표준편차를 빼준 값으로 결정되었다. 전기비저항-P파 속도의 교차출력에 비해 전기비저항과 S파속도를 이용한 교차출력 해석이 제방 시스템의 토양유형, 지반강성 및 암석학적 특성 정보를 보다 충실히 제공하였다. 낮은 S파속도와 높은 전기비저항으로 2사분면에 투영된 느슨한 모래 구역이 취약구간으로 평가되는데 이와 같은 해석은 시추공 표준관입시험에서 보인 중심코어의 N 값 분포로 뒷받침되었다. Specific survey objectives often cannot be met using only one geophysical method, as each method’s results are influenced by the specific physical properties of subsurface materials. In particular, areas susceptible to geological hazards require investigation using more than one method in order to reduce risks to life and property. Instead of analyzing the results from each method separately, this work develops a four-quadrant criterion for classifying areas of levees as safe or weak. The assessment is based on statistically determined thresholds of seismic velocity (P-wave velocity from seismic refraction and S-wave velocity from multichannel analysis of surface waves) and electrical resistivity. Thresholds are determined by subtracting the standard deviation from the mean during performance testing of this correlation technique applied to model data of four horizontal and inclined fracture zones. Compared with results from the crossplot of resistivity and P-wave velocity, crossplot analysis using resistivity and S-wave velocity data provides more reliable information on the soil type, ground stiffness, and lithological characteristics of the levee system. A loose and sandy zone (represented by low S-wave velocity and high resistivity) falling within the second quadrant is interpreted to be a weak zone. This interpretation is well supported by the N values from standard penetrating test for the central core.

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.

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%.

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.