열탄성 구조물의 최적설계

조희근(Cho Hee-Keun),박영원(Park Young-Won) 한국정밀공학회 2000 한국정밀공학회 학술발표대회 논문집 Vol.2000 No.10월

전단농화 유체가 함침된 케블라 방탄재의 충돌 성능해석

조희근(Hee-Keun Cho) 한국기계가공학회 2017 한국기계가공학회지 Vol.16 No.6

This study investigated Kevlar fabric impregnated with shear thickening fluid (STF). The STF performance was assessed by comparing bullet-proof characteristics of STF impregnated and pure Kevlar material. The analysis employed a circular steel ball as the nominal warhead, and bulletproof characteristics were evaluated by the warhead residual velocity. Various initial velocity conditions were employed, with different bulletproof characteristics apparent for each velocity region. The results of this study provide effective data for future bulletproof material design and application.

용사 코팅된 그레이트바의 고온 내마모 특성 평가

조희근(Hee-Keun Cho),안진효(Jin-Hyo Ahn) 한국기계가공학회 2017 한국기계가공학회지 Vol.16 No.5

The grate bar, a component used in steel mills, is used in harsh environments where external disturbances such as high temperature, abrasion, corrosion, and impacts are present. Therefore, in this study, spray-coating was performed on the most severely affected surface to extend the lifetime of the grate bar. The thermal and mechanical properties of the sprayed coated bars were investigated based on the performances under abrasion, thermal shock, tension, and sand blasting, and the microstructures by microscope. By analyzing the thermal and mechanical properties of the uncoated original grate bar and coated grate bar and comparing them with one another, the physical performance improvement of the coated grate bar can be verified.

Optimization of Joint Hole Position Design for Composite Beam Clamping

Hee-Keun Cho(조희근) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.2

In recent years, the use of composite structures has become commonplace in various fields such as aerospace, architecture, and civil engineering. In this study, A method is proposed to find optimal position of bolt hole for fastening of composite structure. In the case of composites, stress distribution is very complicated, and design optimization based on this phenomenon increases difficulty. In selecting the optimum position of the bolt hole, the response surface method(rsm), which is a method of optimization, was applied. A response surface was created based on design points by multiple finite element analyzes. The position of the bolt hole that minimizes the stress when bolting on the response surface was found. The distribution of the stress at the position of the optimal hole was much lower than that of the initial design. Based on the results of this study, it is possible to increase the design safety factor of the structure by appropriately selecting the position of the bolt hole according to various load types when designing the structure and civil structure.

퇴화 쉘 요소를 사용한 적층복합재의 증분형 비선형 좌굴 현상 및 적층 레이업 효과

조희근(Hee-Keun Cho) 한국기계가공학회 2016 한국기계가공학회지 Vol.15 No.1

Laminate composites have a number of excellent characteristics in aspects of strength, stiffness, bending, and buckling. Buckling and postbuckling analysis of laminate composites with layups of [90/0]2s, [±45/90/0]s, [±45]2s has been carried using the Total Lagrangian nonlinear Newton-Raphson method. The formulation of a geometrically nonlinear composite shell element based on a nonlinear large deformation method is presented. The used element is an eight-node degenerated shell element with six degrees of freedom. Square, circular cylinder, and arch panel laminate geometries were analyzed to verify the effects of the layups on the buckling and postbuckling behavior. The results showed that the effects of laminate layups on bucking and postbuckling behavior and the present formulation showed very good agreement with existing references.

과학기술위성 3호 홀추력기 추진계 개발

조희근(Hee-Keun Cho),유광선(Kwangsun Ryu),차원호(Won-Ho Cha),이종섭(Jong-sup Lee),서미희(Mi-Hee Seo),최원호(Won-Ho Choi),명로훈(Noh-Hoon Myung) 한국항공우주학회 2010 韓國航空宇宙學會誌 Vol.38 No.8

최신기술이 적용된 천구조 복합재 위성인 과학기술위성 3호 (STSAT-3)가 국내 최초로 재발 되었으며 2011년 발사예정이다. 모든 위성과 마찬가지로 과기 3호에는 다수의 탑재체가 탑재될 예정이며 그 주된 목적은 선진 우주기술의 과학적 검증에 있다. 제논 가스를 연료로 하는 홀추력기가 국내 최초로 개발되어 지상시험을 거친 후 과기3호에 탑재되었다. 본 연구는 홀추력기 개발에 적용된 전반적언 개발기술, 절차, 기능 빛 환경시험에 대한 내용이며 선진 우주기술 획득 및 차후 위성개발을 위한 기술자료 축적에 그 중요성이 있다. The STSAT-3 (science and technology satellite) is the first satellite whose entire structure was made of composite materials in Korea and it will be launched later in 2011. As like other small satellites, it is also equipped with several advanced instruments whose major objectives focused on the scientific tests in space. The HPS (hall thruster propulsion system) using xenon gas as a propellant has been developed and its overall ground tests were conducted. This research emphasizes on the technologies and procedure applied to the development of the entire HPS and its function and environment tests.

선재압연 설비의 실시간 진단 및 운전감시 프로그램 개발

조희근(Hee Keun Cho) 한국생산제조학회 2021 한국생산제조학회지 Vol.30 No.6

In this study, a monitoring system for multiple high-speed rolling mills in a steel manufacturing factory was developed. Rolling is a core device in a steel mill with a complex system composed of various processes and power transmission systems. A monitoring system was developed that can efficiently manage the entire rolling process through analysis of various mechanical elements, such as, power transmission, rolling, bearings, system analysis, efficiency, fatigue, and additionally computational analysis. The core monitoring factors include the load capacity, fatigue life, bearing life, power consumption, efficiency, etc. and the overall system management program was developed by synthesizing the interrelationships between these process parameters. The interrelationship between each process and device was identified and the monitoring system was optimized.

CNT와 Graphite 나노/마이크로 입자 배열에 의한 나노복합재의 제작과 기계적 강성 및 방사능 차폐 특성 평가

조희근 ( Hee Keun Cho ) 한국복합재료학회 2013 Composites research Vol.26 No.6

복합재료 중 가장 많이 사용되는 탄소계 나노복합재의 성능 향상에 대한 연구가 수행되었다. 나노 사이즈의 탄소나노튜브(CNT)와 마이크로 사이즈의 그레파이트(Graphite) 입자를 일정한 형태로 배열하여 나노복합재를 제작하였다. 입자를 배열하기 위하여 전기장을 활용하였다. 일정한 방향 혹은 형태로 배열된 입자는 에폭시 기지 속에서 섬유강화 복합재 처럼 일정한 방향으로 강성의 향상을 나타낸다. 복합재의 구조적 강성이나 물리적 특성은 강화 입자의 배열상태에 따라 매우 달라지게 된다. 본 연구에서는 특히 탄소나노튜브와 그레파이트 강화입자의 전기장 배열에 의해서 만들어진 나노복합재의 강성 및 방사능 차폐특성을 규명하였다. 전기장에 의한 입자의 배열로 만들어진 탄소계 복합재는 구조적 성능뿐만 아니라 물리적인 방사능 차폐에서도 훌륭한 특성을 나타내었다. Carbon particle based nanocomposites have been studied. Nanocomposites containing CNT and graphite particles were manipulated by aligning the micro/nano-size particles with electric field. Electric field is applied to the suspension of epoxy matrix and particulate inclusions in order to align them along the direction of the electric field. Particles aligned in a uniform direction act as a fiber in a CFRP composite. The mechanical strength and physical characteristics highly depend on particles` distribution pattern and amount. In this study, the characteristics of radioactive barrier are emphasized, which has been rarely discussed in the literature. A number of sample coupons were tested to verify their performance. The procedure of manufacturing nanocomposites by means of extremely small size particle alignment is presented in sequence. Several physical and structural performances of composites containing aligned and randomly distributed particles were compared. The results show particle alignment is very effective to enhance directional strength and radioactive barrier performance.

Thermal Impact Evaluation on Buckling of Cylindrical Structures Using Shell Elements

Hee-Keun Cho(조희근) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.1

Asymptotic 균질화법을 활용한 샌드위치패널로 제작된 위성 구조체의 동적 거동 분석

조희근(Hee Keun Cho) Korean Society for Precision Engineering 2013 한국정밀공학회지 Vol.30 No.11

Korea’s first Naro-Science small class satellite was launched by Naro launcher in 2013. The structure of the satellite is mostly composed of aluminum honeycomb and frame. The honeycomb structure is homogenized with asymptotic homogenization method and its mechanical properties were used for the numerical analysis. There have been some difficulties to modeling the honeycomb sandwich panels for FEA. In the present study, the mechanical characteristics of the sandwich panel composite were numerically computed and used for the simulation. This methodology makes it easy to overcome the weakness of modeling of complicated sandwich panels. Both an experiment of vibration test and numerical analyses were conducted simultaneously. The analysis results from the current homogenization were compared with that of experiment. It shows a good agreement on the dynamic responses and certified the reliability of the present methodology when manipulate sandwich panel structure.