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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.
김석봉(Seokbong Kim),허훈(Hoon Huh),신철수(Chirlsoo Shin),김효균(Hyokun Kim) 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.1
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 paper 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 increases as strain rate increases; the strain hardening decreases as the tensile stress increases. The experiments also produce interesting results that the elongation does not decrease even when the strain rate increases.
김석봉(Seokbong Kim),이경호(Kyungho Lee),허훈(Hoon Huh),유정수(Jungsu Yoo),이문용(Munyong Lee) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
This study deals with the crashworthiness of aluminum crash box for an auto-body with the various types of cross section. For the aluminum alloy, Al7003-T7, the dynamic tensile test was carried out to apply for crash analysis at the range of strain rate from 0.003/sec to 200/sec. The crash analysis was carried out for four cross sections, square and hexagonal with and without ribs. The analysis result shows that the absorbed internal energy and the reaction force of crash box with rib are higher than that of crash box without rib. This result is due to the interaction between member and rib and the collapse of rib with the buckling mode. And the energy absorption is also affected by the cross section shape. Hexagonal cross section shows higher energy absorption and reaction force than square cross section.
김석봉(Seokbong Kim),안광현(Kwanghyun Ahn),하지웅(Jiwoong Ha),이창수(Changsoo Lee),허훈(Hoon Huh),복현호(Hyunho Bok),문만빈(Manbeen Moon) 한국자동차공학회 2010 한국 자동차공학회논문집 Vol.18 No.1
This paper deals with the formability of DP590 steel considering the strain rate. The strain hardening coefficient, elongation and r-value were obtained from the static and dynamic tensile test. As strain rate increases from static to 100/s, the strain hardening coefficient and the uniform elongation decrease and the elongation at fracture and r-value decrease to 0.1/s and increase again to 100/s. The high speed forming limit tests with hemi-spherical punch were carried out using the high speed crash testing machine and high speed forming jig. The high speed forming limit of DP590(order of 10²/s) decreases compared to the static forming limit(order of 10?³/s) and the forming limit band in high speed forming test is narrower than that in the static forming test. This tendency may be due to the development of brittleness with increase of stain rate.
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.
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.
예비변형률 효과를 고려한 차체용 박판의 동적 물성 특성 연구
김석봉(Seokbong Kim),임지호(Jiho Lim),허훈(Hoon Huh) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Most parts of auto-body are produced through the sheet metal forming process, and during this process they have change of thickness and residual stress and strain remain. In this paper, to specify dynamic material properties considering this pre-strain effect, materials SPCEN, SPRC45E and SPRC35R were selected and were imposed 5, 10% pre-strains. After that using the high speed material testing machine, materials were tested at given strain rates of between 0.003 and 50 s^-¹. It was found from experimental results that in case of SPCEN and SPRC35R, the yield stress and ultimate stress were increased due to pre-strain effect at strain of over 10 s^-¹ but SPRC45E was not affected by pre-strain effect.
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.