• Proceedings of the KSME Conference
• /
• 2005.11a
• /
• pp.145.2-145.2
• /
• 2005

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.11
• /
• pp.762-769
• /
• 2017

The extensional stiffness in quasi-isotropic laminates is uniform in the radial direction, but the bending stiffness varies radially due to the stacking sequence. This paper addresses the directional dependency of the bending stiffness and its radial variation in three types of quasi-isotropic laminate reflectors consisting of unidirectional fiber composite materials (UDM) and randomly distributed composite materials (short fiber, RDM). The extensional stiffness and bending stiffness in optical reflectors using RDM are uniform, while the bending stiffness in those using UDM varies radially from 11% to 26%. Also, the stiffness sensitivity, such as the bend-twist or bend-torsion effect, due to the differences in the stiffness value in the composite, is large. These factors are problematic in the optical field requiring precision surfaces. Utilizing RDM might be one way to eliminate the presence of bending stiffness in composite mirror substrates.

• Korean Journal of Optics and Photonics
• /
• v.25 no.4
• /
• pp.207-215
• /
• 2014

In this paper the radial stiffness associated with stacking sequence effects, and the dimensional stability issue associated with thermally induced surface deformation in quasi-isotropic laminates due to the effect of stacking sequence and additional resin layer technique, are numerically investigated. Finally, the influence of surface resin layer techniques for fiber print-through mitigation in a composite mirror is tested for evaluation of surface accuracy across varying thermal conditions.

• The Optical Journal
• /
• s.104
• /
• pp.23-25
• /
• 2006

프린터 시장은 삼성과 HP가 전체 시장의 60% 이상 과점상태를 보이고 있지만 후발업체들이 추격을 강화하는 가운데, 전체 시장은 소폭의 성장과 함께 가격하락세를 보이고 있다. 지난해 프린터 시장은 잉크젯에서 컬러 레이저로, 프린터 단품에서 복합기로의 변화를 거듭했다. 지금까지 프린터 시장을 주도해왔던 잉크젯 단품 제품은 지난해 정점을 찍으면서 앞으로 점차 수요가 감소하고 이 자리를 컬러 레이저와 복합기가 차지할 것으로 보인다.이런 전망에 확신을 실어주듯 지난해 컬러레이저 시장은 성장성이 높은 시장으로 떠오르며 시장경쟁이 가장 치열했다. 또한 향후에는 컬러 레이저 제품이 급속도로 성장할 것으로 전망되며, 복사기 및 프린터 업체들이 공통으로 기업용 솔루션 관련 시장을 본격 공략하며 치열한 경쟁관계를 형성할 것으로 보인다.

• Composites Research
• /
• v.13 no.2
• /
• pp.22-29
• /
• 2000

Although C/C composites have excellent mechanical properties at high temperature, the disadvantage of oxidation in air restricts their applications. Thus a lot of investments have been studied to improve this drawback. In this study, SiC used as a thermal protective coating material possesses almost the same expansion coefficient compared to that of carbon, so SiC was coated on 4D C/C composites by Pack-Cementation process. For SiC-coated C/C composites, optical microscopy observations were performed to estimate the conversion mechanism involved and air oxidation tests were also performed to evaluate the improvement of oxidation resistance. Afterwards the optimum conditions of coating process were estimated from the results of several analysis and tests.

• The Optical Journal
• /
• s.130
• /
• pp.29-35
• /
• 2010

군사용 전자광학장비는 정보지식 기반의 현대무기체계에 필수적인 장비로 발전하고 있다. 그러나 광학부품의 원소재나 영상증폭관, 열상검출기 등의 일부 핵심부품은 여전히 해외도입에 의존하고 있으며, 항공기나 위성에 탑재되는 감시정찰용의 복합시스템에 대한 체계설계기술 역시 아직 미흡한 실정이다. 따라서 향후 군사용 전자광학장비의 완전한 자립을 위한 연구협력체 구성과 이를 통한 국제경쟁력 제고가 필요하다.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.2
• /
• pp.192.2-192.2
• /
• 2012

위성시스템 소형화, 탑재체 수용증대, 발사비용절감, 탐사임무 효율화 등의 요구로 인하여, 위성 설계에 있어 경량화는 오랜 기간 진행되어온 연구 주제였다. 이러한 연구결과로서, 위성 구조체를 복합재료로 대신하기 위한 구조 경량화 연구와 적용이 성과를 거두었으며, 현재 위성체 프레임이나 전개형 안테나, 광학구조물 등에 경량 탄소섬유 강화 복합재료의 적용은 보편화되어 있다. 한편, 위성시스템에서 전력, 통신, 명령/데이터처리, 자세제어 및 관측기기의 각종 전자장비를 보호하는 하우징 구조물에는 여전히 금속재료가 광범하게 적용되고 있다. 특히, 알루미늄 합금은 하우징 재료로 널리 사용되는데, 강도, 강성, 열전달, 우주방사, 전기전도도 및 EMI 차폐특성과 더불어 가공성이 우수하다는 장점을 지닌 반면에, 금속재료로서 중량이 상당하여 위성 경량화 관점에서는 한계를 갖게 하는 단점이 있다. 전자장비에 부여된 전자기능 측면에서 보면, 하우징은 기생 구조물로서, 경량으로 제공될수록 전자장비 전체 무게에서 전자유닛만의 무게가 차지하는 전기전자기능비가 향상되고 위성 경량화에 크게 기여할 수 있다. 구조 경량화를 위하여 전자장비 하우징을 경량 복합재로 대체하여 설계 및 제작하였으며, 복합재 하우징의 강도, 강성, 열전달, 우주방사, 전기전도도 및 EMI 차폐를 검증할 수 있는 방법에 대하여 검토하였다.

• Composites Research
• /
• v.24 no.2
• /
• pp.14-21
• /
• 2011

In this paper, a dynamic model is proposed for multi-axis optical structure of an aircraft. Modal analysis, sine-wave analysis, and random vibration analysis are done using a multi-body dynamic program for the multi-axis optical structure. By applying Al 6061-T6 and two types of CFRP to the camera module, x, y, and z responses are found and compared according to each axis excitation. The results will be used for reducing the weight of the camera module.

• Composites Research
• /
• v.27 no.2
• /
• pp.52-58
• /
• 2014

Short fiber reinforced composites manufactured by injection molding have diverse fiber orientations variable with measuring positions even in the same specimen, which is caused by the flow induced fiber orientation. Fiber orientations considerably affect the mechanical and thermal properties of final composite products. In this study, fiber orientation of injection molded carbon fiber reinforced PA6/PPO composite was measured at several points of the specimen by optical microscopy analysis and the corresponding izod impact strength, coefficients of thermal expansion (CTE) were also measured to investigate the influence of local fiber orientation on the mechanical and thermal properties. Izod impact strength where fiber was perpendicular to the direction of crack propagation was higher than where fiber was parallel to the direction, which could be explained be the impact resistance reinforcing mechanism by fiber orientation. CTE was also lower where fiber was parallel to the measurement direction of CTE than where fiber was perpendicular to the direction, which could be also explained by the dimensional stability mechanism by fiber orientation.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.26 no.6
• /
• pp.21-27
• /
• 2022

C_f/SiC composites have low density, high mechanical strength, and good thermal stability, making them promising materials for high-temperature applications such as rocket propulsion and military fields. However, the remaining Si deteriorates physical and thermal properties. In this paper, the de-siliconization was introduced as a method to remove the Si of the C_f/SiC composite fabricated through Liquid Silicon Infiltration(LSI) process. The stability of composite has been tested under an oxyacetylene torch flame for up to 5 minutes. The oxidized surface and cross section of specimens were characterized by 3D scanning, X-ray diffraction(XRD), Optical microscope(OM) and Scanning electron microscope(SEM).