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김석봉,유요한,Kim, Seokbong,Yoo, Yohan 한국군사과학기술학회 2015 한국군사과학기술학회지 Vol.18 No.2
This paper deals with the effect of concrete target size on penetration of projectiles. We investigated the penetration depth and residual velocity of projectiles using the 2-D axial symmetric model. Most analysis were conducted with 13 kg projectile (striking velocity: 456.4 m/s) and concrete target with compressive strength of 39 MPa. This paper provided penetration depth (or residual velocity) versus ratio D/d (target diameter, D and projectile diameter, d). When the bottom of concrete cylinder was constrained, penetration depth converged to limit depth more than the ratio D/d of 36. The residual velocity of projectile with thin concrete target were investigated. The residual velocity was converged to specific velocity more than the ratio D/d of 16.
김석봉,이창수,유요한,Kim, Seokbong,Lee, Changsoo,Yoo, Yohan 한국군사과학기술학회 2017 한국군사과학기술학회지 Vol.20 No.2
This paper deals with the scale effects of warhead on concrete penetration. We investigated the scale effects using finite element analysis and Young's penetration equation. As the scale of penetration test decreases, the strain rate effects of target increases, and then strength of concrete target increases. This means the residual velocity and penetration depth of warhead decreases as the test model size decreases. Young's penetration equations are transformed with various penetrator mass and scale cases as a function of scale ratio. Penetration distance and residual velocity are not simply changed by the geometric scaling law.
김석봉(Seokbong Kim),허훈(Hoon Huh),임지호(Jiho Lim),김기풍(Keepoong Kim) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_3
An important challenging issue in the automotive industry is the light-weight, safe design and enhancement of crash response of an auto-body structures. These objectives lead to increasing adoption of TRIP-type and DP-type steel sheets for an inner part of auto-body members. This study evaluates the dynamic tensile characteristics of TRIP60. TRIP80, DP60 and DP80 at the range of strain rate from 0.003/sec to 200/sec. The tensile tests acquire stress-strain relation and fracture elongation of each material. The experimental results show that the flow stress is increased as strain rate increases and elongation is not decreased even when the strain rate increases. In order to investigate the pre-strain effect at high strain rate, TRIP60 and DP60 were deformed with 5, 10% pre-strain at 0.003/sec strain rate. Then dynamic tensile test was carried out at the strain rate of 0.003, 1, 10, 100/sec. The results demonstrate that the material properties are noticeably influenced by the pre-strain at the high strain rate. The ultimate tensile strength as well as the yield stress is increased due to the pre-strain.
상사의 비인격적인 행동, 리더호감 및 과업성과 간의 관계 연구 : 구성원 친교욕구의 조절된 매개효과
김석봉(Kim, Seokbong),박희태(Park, Heetae) 한국인적자원관리학회 2021 인적자원관리연구 Vol.28 No.4
본 연구는 조직 내 부정적 리더십의 한 형태로 관심을 받고 있는 상사의 비인격적 행동이 구성원의 과업성과에 미치는 과정을 살펴보았다. 상사의 비인격적 행동이 과업성과에 미치는 과정에서 매개변수로써 구성원이 인식한 상사에 대한 호감(이하 리더호감)과 조절변수로서 구성원의 내적 특성인 친교 욕구를 살펴보았다. 변수 간 관계를 검증하기 위하여 설문 조사를 통하여 변수들을 측정하였으며, 다양한 조직이나 회사에 근무하고 있는 구성원을 대상으로 구글(google) 설문지로 작성하여 페이스북을 통해 배포 및 173부를 회수하였다. 실증연구 결과 상사의 비인격적 행동과 구성원의 과업성과 간의 관계에서 리더 호감의 매개효과가 검증되었다. 상사의 비인격적인 행동이 높을수록 리더호감은 감소하였고, 그 결과 과업성과에 부정적인 영향을 미치는 것으로 나타났다. 그리고 구성원의 친교욕구는 상사의 비인격적 행동, 리더호감, 과업성과 간의 관계에서 조절된 매개효과가 검증되었다. 즉, 친교욕구가 높은 구성원은 낮은 구성원보다 상사의 비인격적인 행동에 따른 리더호감이 더 강하게 감소하였고, 과업성과에도 더 강한 부정적인 영향을 미치는 것으로 나타났다. 연구결과에 따른 시사점과 연구 한계점 및 향후 연구방향을 제시하였다. This study examined the process by which abusive supervision, which is receiving attention as a form of negative leadership within the organization, affects the task performance of the subordinate. In the process of abusive supervision on task performance, we examined the leader liking recognized by the subordinate and the need for friendship, which is the internal characteristic of the subordinate as a moderating variable. To verify the relationship between the variables, the variables were measured through a survey, and a Google questionnaire was prepared for members working in various organizations or companies, distributed through facebook, and 173 copies were collected. As a result of the empirical study, the mediating effect of the leader liking was verified on the relationship between abusive supervision and task performance. As the abusive supervision was higher, the leader liking decreased, and as a result, it was found to harm task performance. In addition, the moderated mediating effect of the desire for friendship was verified in the relationship between abusive supervision, leader liking, and task performance. In other words, it was found that subordinate with a high desire for friendship had a stronger decrease in leader preference due to the abusive supervision than those with low desire for friendship, and had a stronger negative effect on task performance. Implications, limitations, and future research directions according to the research results are presented.
김석봉(Seokbong Kim),허훈(Hoon Huh),김대온(Daeon Kim),문만빈(Manbin Moon) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
An important challenging issue in the automotive industry is the light-weight, safe design and enhancement of crash response of an auto-body structures. These objectives lead to increasing adoption of high strength steel sheet for inner and outer auto-body members. This study evaluates the dynamic tensile characteristics of high strength steel sheets, HS45R, TRIP60, DP60 and DP100, along the rolling direction and transverse direction. Static tensile tests were carried out at the strain rate of 0.003/sec using the static tensile machine (Instron 5583). Dynamic tensile tests were carried out at the range of strain rate from 0.1/sec to 200/sec using a high speed material testing machine developed. The tensile tests acquire stress-strain relation and strain rate sensitivity of each material. The experimental results show two important aspects for high strength steels: the flow stress is increased as strain rate increases; the strain hardening is decreased as the tensile stress increases. The experiments also produce interesting results that the elongation is not decreased even when the strain rate increases.
김석봉(Seokbong Kim),안광현(Kwanghyun Ahn),하지웅(Jiwoong Ha),허훈(Hoon Huh),복현호(Hyunho Bok) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
This paper deals with the formability of CQ and DP590 steel sheets in relation to the strain rate. The high speed forming limit tests were performed using the high speed crash testing machine and high speed forming jig. Compared with the static FLC, the high-speed FLC of CQ is higher in a simple tension region and lower in a biaxial stretch forming region. The high-speed FLC for DP590 decreases in relation to the static FLC throughout the entire region. The elongation at fracture appears to be closely related to the simple tension region of the FLC. The decrease of the high-speed FLC in the biaxial stretch forming region is due to the shear fracture in fracture surfaces. Three theoretical (Hill?Swift, Jun and M?K models) approaches and two empirical (Keeler?Brazier and Raghavan models) approaches were discussed to predict the FLC of sheet metals. The theoretical models are found to be very conservative, especially at plane strain region in FLC. Among the various prediction models, the Raghavan model with NADDRG curve gives better prediction at plane strain region.
예비변형률 효과를 고려한 고변형률 속도에서의 차체용 강판의 물성 특성
김석봉(Seokbong Kim),임지호(Jiho Lim),허훈(Hoon Huh),임종대(Jongdae Lim) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Most auto-body members fabricated by the sheet metal forming process. During this process the thickness and material properties of the sheet metal are changed with the residual stress and plastic strain. This paper deals with the material properties of the sheet metal at the high strain rate considering the pre-strain effect. Specimens are selected from sheet metals for outer panels and inner members, such as SPCEN, SPRC45E, SPRC35R and EZNCD. The specimens are prepared with the prestrain of 2, 5 and 10 % by tensile elongation in Instron 5583, which could be equivalent to the plastic strain in sheet metal forming, High speed tensile tests are then carried out with the pre-stained specimens at the strain rate of 1 to 100 /sec. The experimental result informs that the material properties are noticeably influenced by the pre-strain when the yield stress of the specimens is moderate as SPCEN, SPRC35R and EZNCD. The result also demonstrates that the ultimate tensile strength as well as the yield stress is increased as the amount of the pre-strain is increased.