압축잔류응력이 스프링강의 고온환경 피로균열 진전거동에 미치는 영향

정찬기(CHAN-GI JUNG),박경동(KEYOUNG-DONG PARK) 한국해양공학회 2002 韓國海洋工學會誌 Vol.16 No.5

In this paper, the effect of the compressive residual stresses was obtained at the test conditions of the higher temperature than the ambient temperature. The examination was performed with the CT specimen result of the material(JISG SUP9) which is being commonly used for the marine engine parts and the ocean structures. As a result, the test conditions at the higher temperature were acquired considering the peak values of the compressive residual stresses of the specimens and the effect on the fatigue crack propagation speed da/dN in stage Ⅱ and the threshold stress intensity factor range ΔKth in stage Ⅰ. Also the material constant C and the fatigue crack propagation index m in the formula of Paris Law da/dN=(ΔK)<SUP>m</SUP> were suggested to estimate the dependence on the test temperature.

대학 및 개인 특성이 취업여부에 미치는 영향 분석

왕정원(Jung Won Wang),정찬기(Chan Gi Jung),심관용(Gwan Yong Sim) 한국지방교육경영학회 2020 지방교육경영 Vol.23 No.1

대학진학은 우리나라에서 신분상승의 수단으로 여겨져 높은 대학진학률을 보이고 있다. 이에 대학 입학정책은 민감한 국민적 관심사이며, 정부는 대학정책에 지속적인 어려움을 겪어왔고 대학입시정책의 잦은 변화를 야기해왔다. 이러한 대학 입학전형의 변화는 대학들이 우수 인재 확보에 많은 노력을 기울이게 하고 있다. 우수 인재들을 확보한 대학의 효과성을 확인할 수 있는 지표 중 하나는 취업률로 확인할 수 있다. 본 연구는 대학들이 대학 입학전형에 따라 우수인재를 확보하였을 때, 개인배경, 대학에서의 경험, 교수학습만족도, 대학지원제도 만족도 등이 취업에 미치는 영향에 대해 분석하였다. 연구 결과, 수시전형으로 들어온 학생보다 수능위주전형으로 들어온 학생이 취업해 있는 경우의 비율이 높았다. 교수학습만족도 특성에서는 교수진의 능력 및 열의가 유의한 영향을 미친 것으로 나타났다. 대학서비스 부분에서는 학생에 대한 진로관련 상담 및 지원제도가 좋을수록 취업할 확률이 높은 것으로 나타났다. 졸업평점의 경우 평점이 높을수록 취업할 확률이 낮은 것으로 결과 값이 도출되었으나, 그 차이는 퍼센트로 나타났다. 개인특성 중 유의한 결과를 보인 것으로는 부모의 학력이 높을수록 그렇지 않은 집단에 비해 취업할 확률이 낮은 것으로 나타났다. 개인의 대학특성에서의 유의한 결과는 지방권 대학들이 수도권보다, 사립대학이 국·공립대학들에 비해 취업할 확률이 높은 것으로 나타났다. 대학계열 별로는 인문계열에 비해 사회계열, 예체능계열, 의학계열이 높은 것으로 나타났다. College admission is considered a means of raising one's status in Korea, so it has a high college entrance rate. The university admission policy has been a sensitive national concern, and the government has suffered continuous difficulties in university policy and has caused frequent changes in college admission policy. This change in college admission is causing universities to put a lot of effort into securing talented people. One of the indicators for the effectiveness of universities with outstanding talent is the employment rate. This study analyzed the influence of university on employment, such as college admission transfer, personal background, experience in university, satisfaction with teaching experience, and satisfaction with college application system. As a result, students who entered the college entrance exam were 0.657 times lower than those who entered the college entrance exam at a significant level of 0.01 in terms of the impact of employment. Among the variables for teaching satisfaction, the faculty's ability and enthusiasm were found to be 0.919 times lower than those for those who did not at a significant level of 0.05 level. Among college application system satisfaction, career counseling and support systems were found to be 1.217 times more likely to be employed than those who did not have the support system at a significant level of 0.01 level. Among college environment satisfaction, education support facilities are 0.926 times less likely to get a job than those that are not at a significant level. Students with high graduation grades were 0.995 times less likely to get a job at a significant level of 0.01 than those who did not. Statistically significant individual characteristics have shown that the higher the parents' educational background, the more adverse the chances of getting a job.As a result of school location and university type, the local area was more likely to get a job than the metropolitan area. Private universities are more likely to get jobs than national and public universities. In the major category, the social and medical sectors were less likely to get a job than the humanities, while the arts and physical education classes were higher.

국방 사이버 침해 대응을 위한 전산보안점검 프로그램 및 사용자 진단항목 개선 연구(육군 중심)

김지원,정의섭,정찬기,Kim, Jee Won,Jung, Ui Seob,Jung, Chan Gi 한국융합보안학회 2017 융합보안 논문지 Vol.17 No.2

최근 해킹, 바이러스 등 대한민국을 노린 공격이 증가하고 있다. 이와 마찬가지로 우리 군도 사이버 침해에 대한 노출이 심해지고 있으며 이를 대응하기 위해 국방부는 사이버 안보에 대한 기본절차를 규정하고 지침을 제공하고 있다. 그럼에도 불구하고 육군에서 발간하는 사이버방호작전 분석결과를 보면 침해건수는 점점 증가하고 있다. 이에 대한 문제점들을 개선하고자 사이버 침해 대응을 위해 가장 중요하면서 기본인 사용자 환경에서의 전산보안 점검항목을 재점검하여 안전하고 효율적인 전산보안 점검항목을 제시한다. Recent cyber attacks on South Korea, including hacking and viruses, are increasing significantly. To deal with the cyber invasion of cyber aggression, the Ministry of National Defense defined the necessary procedures for cyber security with guidelines for cyber security. In spite of, based on the analyses the cyber defense operations published, the number of violations are increasing. To address issues stated above, the safety check items should be reviewed and revised. This paper will revisit current safety check items and provide new guidelines to prevent cyber security breaches, which will provide more safe and efficient cyber environment.

스프링강의 피로크랙 진전거동에 미치는 압축잔류응력의 영향

박경동(Keyoung-Dong Park),정찬기(Chan-Gi Jung) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3

Nowadays, many components used in machinery industry is required lightness and high strength. Therefore, the effects of compressive residual stress by shot-peening which is method to improve fatigue lift of (JISG SUP-9), which used in suspension of automobile, on fatigue crack growth characteristics was investigated with considering fracture mechanics. So, we can obtain followings. (1) The fatigue crack growth rate on stage Ⅱ is conspicuous with the size of compressive residual stress and is dependent on Paris equation. (2) Although the maximum compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maximum compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress. (4) In fracture surface of fatigue crack growth it is investigated that compressive residual stress remarkably retards fatigue crack growth.

압력용기용 합금강의 저온 피로 특성에 관한 연구

박경동(Kyung-Dong Park),정찬기(Chan-Gi Jung),하경준(Kyung-Jun Ha),박형동(Heyoung-Dong Park),전보훈(Bo-Hun Jeun) 한국동력기계공학회 2000 한국동력기계공학회 학술대회 논문집 Vol.- No.-

DIN50CrV4-SAE9254강의 피로강도에 미치는 압축잔류응력의 영향

박경동(KYUNG-DONG PARK),정찬기(CHAN-GI JUNG) 한국해양공학회 2001 韓國海洋工學會誌 Vol.15 No.3

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, two kinds of spring steel (SAE 9254, DIN 50CrV4) are used. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from (1) on low stress condition, the 1st stage shot peening is not affected by nonmetallic inclusion under metal. (2) it is possible that the 2nd stage shot peening increases the fatigue life and the high stress but that is affected by nonmetallic inclusion under metal. (3) so far beeasily DIN50CrV4 have made high stress. But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.

스프링강의 피로크랙 진전거동에 미치는 압축잔류응력의 영향

박경동(Keyoung-Dong Park),정찬기(Chan-Gi Jung) 대한기계학회 2002 대한기계학회 기타 간행물 Vol.2002 No.11

JISG4081SUP7-DIN50GrV4강의 피로강도에 미치는 쇼트피이닝의 영향

박경동(KEYOUNG-DONG PARK),정찬기(CHAN-GI JUNG) 한국해양공학회 2001 韓國海洋工學會誌 Vol.15 No.4

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of shot peening of two-stage shot peening and single-stage shot peening. And for this study, two kinds of spring steel (JISG4081SUP7, DIN 50CrV4) are used. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from on low stress condition, the 1st stage shot peening is not affected by nonmetallic inclusion under metal. it is possible that the 2nd stage shot peening increases the fatigue life and the high stress but that is affected by nonmetallic inclusion under metal, so far beeasily DIN50CrV4 have made high stress. But, results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.

스프링강의 피로파괴에 미치는 압축잔류응력의 영향

박경동(Keyoung-Dong Park),정찬기(Chan-Gi Jung) 한국자동차공학회 2002 한국자동차공학회 지부 학술대회 논문집 Vol.2002 No.10

Due to the desire for light-weight materials to posses superior strength, there is a high demand for research and development of materials that are not heavy yet can still overcome the problems of stress fractures. This study researches the effects of compressive residual stress on spring steel (JISG SUP-9).<br/> In this study, an effect that the compressive residual stress formed by Shot-peening the surface of the spring steel (JISG SUP-9) at each Shot velocity (0, 57, 70, 83, 96m/sec) has on the fatigue crack propagation characteristics under the normal temperature condition was examined. Followings are the results;<br/> (I) In the area of Stage II, the fatigue crack propagation speed da/ dN is slowed as the shot is accelerated, and such tardiness effect reaches a maximum value at the shot velocity of 70m/sec, and then in case the shot is further accelerated over 70m/sec, it is gradually lowered.<br/> (2) In the area of Stage I, as the shot velocity is varied, the compressive residual stress has a considerable effect on the threshold stress intensity factor range ΔΚ tk'<br/> (3) In Paris Law( da/dN= C(Δkm)), C and m'S dependency upon the shot velocity is suggested as in Formula (3), (4), (5) and (6).<br/> <br/>

스프링강의 피로크랙 진전거동에 미치는 압축잔류응력의 영향

박경동(Keyoung-Dong Park),정찬기(Chan-Gi Jung) 한국자동차공학회 2002 한국자동차공학회 Symposium Vol.2002 No.11

In this paper, the effect of the compressive residual stresses which were obtained under the various shot velocities on the fatigue behaviors of a spring steel, were investigated. The examination of CT specimen test were executed with the materials(JISG SUP9) which are beign commonly used for the springs of automotive vehicles. As a result, the optimal shot velocity of shot balls were acquired considering the peak values of the compressive residual stresses on the surface of specimen and effect on the speed of the fatigue crack propagation da/dN in stage Ⅱ and the threshold stress intensity factor range ?? in stage Ⅰ. Also the material constant C and the crack propagation index m in the formula of paris law da/dN=O(??) were suggested in this work to estimate the dependency on the shot velocity.