• 대한기계학회논문집A
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• 제37권1호
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• pp.121-127
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• 2013

최근 경량 자전거에 대한 요구가 지속적으로 증가함에 따라 탄소섬유 복합재료가 자전거 프레임 및 부품 제작에 널리 활용되고 있다. 복합재료는 일반적인 등방성 재료와는 달리 적층판의 방향과 순서에 따라 그 구조적인 특성이 변화하기 때문에 복합재료 자전거의 디자인을 검증하기 위해서는 구조 해석을 수행하는 것이 필수적이다. 본 연구에서는 CFRP 소재를 적용하여 자전거 프레임을 설계하였고, 유한요소해석을 통하여 그 구조적 성능을 분석하였다. 다양한 적층 순서와 하중조건 하에서 섬유와 매트릭스의 파손지수를 측정함으로써 복합재의 적층 조건이 자전거의 구조 강도에 미치는 영향을 분석하였다. 또한 취약 부분은 추가적인 복합재 적층판을 이용하여 보강함으로써 자전거 프레임의 구조적 안전성을 확보할 수 있었다.

• 해양환경안전학회지
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• 제28권7호
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• pp.1222-1230
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• 2022

로터 블레이드는 조류발전 터빈의 매우 중요한 구성 요소로서, 해수의 높은 밀도로 인해 큰 추력(Trust force)와 하중(Load)의 영향을 받는다. 따라서 블레이드의 형상 및 구조 설계를 통한 성능과 복합소재를 적용한 블레이드의 구조적 안전성을 반드시 확보해야 한다. 본 연구에서는 블레이드 설계 기법인 BEM(Blade Element Momentum) 이론을 이용해 1MW급 대형 터빈 블레이드를 설계하였으며, 터빈 블레이드의 재료는 강화섬유 중의 하나인 GFRP(Glass Fiber Reinforced Plastics)를 기본으로 CFRP(Carbon Fiber Reinforced Plastics)를 샌드위치 구조에 적용해 블레이드 단면을 적층(Lay-up)하였다. 또한 유동의 변화에 따른 구조적 안전성을 평가하기 위해 유체-구조 연성해석(Fluid-Structure Interactive Analysis, FSI) 기법을 이용한 선형적 탄성범위 안의 정적 하중해석을 수행하였으며, 블레이드의 팁 변형량, 변형률, 파손지수를 분석해 구조적 안전성을 평가하였다. 결과적으로, CFRP가 적용된 Model-B의 경우 팁 변형량과 블레이드의 중량을 감소시켰으며, 파손지수 IRF(Inverse Reserce Factor)가 Model-A의 3.0^*V_r를 제외한 모든 하중 영역에서 1.0 이하를 지시해 안전성을 확보할 수 있었다. 향후 블레이드의 재료변경과 적층 패턴의 재설계뿐 아니라 다양한 파손이론을 적용해 구조건전성을 평가할 예정이다.

• 한국구조물진단유지관리공학회 논문집
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• 제24권6호
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• pp.102-112
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• 2020

본 연구에서는 교량구조물에 활용할 수 있는 폭 100mm 이상의 대형 탄소판을 고정할 수 있는 쐐기형 정착구를 설계하기 위해서, 주요설계변수인 쐐기의 각도, 정착블록-쐐기 사이의 마찰계수 등을 기준으로 거동특성을 수치해석방법으로 분석하였다. 설계변수 별로 탄소판의 응력상태를 계산하고, 복합재료 파괴기준에 의하여 정착구의 극한상태에서의 성능을 평가하였고, 이를 바탕으로 정착구의 최적설계 제원을 결정하였다. 실물실험을 통하여 최적설계된 정착구의 성능을 검증하였으며, 본 연구의 결과는 대형 구조물을 보강하기 위한 탄소판 정착구의 최적설계에 활용될 수 있을 것으로 판단된다.

• Advances in concrete construction
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• 제9권1호
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• pp.43-54
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• 2020

This paper presents an innovative stress-function variational approach in formulating the interfacial shear and normal stresses in an externally bonded concrete joint using carbon fiber-reinforced plastic (CFRP) plies. The joint is subjected to surface traction loadings applied at both ends of the concrete substrate layer. By introducing two interfacial shear and normal stress functions on the CFRP-concrete interface, based on Euler-Bernoulli beam idea and static stress equations of equilibrium, the entire stress fields of the joint were determined. The complementary strain energy was minimized in order to solve the governing equation of the joint. This yields an ordinary differential equation from which the interfacial normal and shear stresses were proposed explicitly, satisfying all the multiple traction boundary conditions. Lamination theory for composite materials was also employed to obtain the interfacial stresses. The proposed approach was validated by the analytic models in the literature as well as through a comprehensive computational code generated by the authors. Furthermore, a numerical verification was carried out via the finite element software ABAQUS. In the end, a scaling analysis was conducted to analyze the interfacial stress field dependence of the joint upon effective issues using the devised code.

• Composites Research
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• 제24권2호
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• pp.14-21
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• 2011

본 논문에서는 항공기에 장착되는 다축 구동 광학계에 대한 동역학 모델링을 하고, 다물체 동역학 해석프로그램을 사용하여 다축 구동 광학계의 모드해석, 사인파 해석 및 랜덤 진통해석을 하였다. 카메라 모듈의 물성으로는 Al6061-T6와 두 가지 형태의 강화 복합재 물성을 적용하였으며, x, y, z 축의 가진에 따른 각 축의 응답을 구하여 서로 비교하였다. 해석 결과는 카메라 모듈의 경량화를 위해 사용될 수 있을 것으로 사료된다.

• Advanced Composite Materials
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• 제18권1호
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• pp.43-59
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• 2009

The current study assessed the effect of a bolt hole on tensile fatigue properties of CFRP laminates. Two specimens, i.e. $[(0/90)_3]S$, $[(0/45/90/-45)_2]_S$, were analyzed using a finite element method and were experimentally tested for cases, both with and without a hole, whose diameter corresponded to 0.12 times the specimen width. Delamination positions predicted by a 3-dimensional static finite element analysis were matched well to those observed by an ultrasonic imaging system in the middle of fatigue test. A hole whose diameter corresponds to 0.12 times the specimen width caused the fatigue strength to decrease by 9% and 11% under 5 Hz loading frequency, and by 22% and 25% under 10 Hz loading frequency for $[(0/90)_3]_S$ and $[(0/45/90/-45)_2]_S$, respectively. Because the decrease in sectional area due to the hole was normalized in calculation of the tensile strength, a stress concentration around the hole is believed to induce the strength degradation of fatigue specimens. From the finite element analyses, the stress concentration factor around a hole was expected as 8.8 and 9.5 for $[(0/90)_3]_S$ and $[(0/45/90/-45)_2]_S$, respectively.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2328-2335
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• 2002

A hybrid composite material has many potential usage due to the high specific strength and the resistance to fatigue, when compared to other composite materials such as fiber reinforced plastic(FRP) and metal matrix composite(MMC). However, the fracture mechanism of hybrid composite material is extremely complicated because of the bonding structure of metals and FRP. In this study, Al 7075 sheets and carbon epoxy preprags were used to fabricate the hybrid composite. Recently, nondestructive technique has been used to evaluate the fracture mechanism of these composite materials. AE technique was used to clarify the microscopic damage behavior and failure mechanism of A17075/CFRP hybrid composite. It was found that AE paralneters such as AE event, energy and amplitude were effective to evaluate the failure process of Al 7075/CFRP composite. In addition, the relationship between the AE signal and the characteristics of fracture surface using optical microscope was discussed.

• 대한기계학회논문집A
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• 제20권6호
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• pp.1836-1842
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• 1996

In this paper, static and fatigue bending strengths of CFRP(carbon fiber reinforced plastic laminates having impact damage(FOD) are evaluated. Composite laminates used for this experiment are CF/EPOXY and CF/PEEK orthotropy laminated plates, which have two-interfaces[${0^0}_4{90^0}_4}$]$_sym$. A steel ball launched by the air gun colides against CFRP laminates to generate impact damages. The damage growth during bending fatigue test is observed by the scanning acoustic microscope(SAM). When the impacted side is compressed, the residual fatigue bending strength of CF/PEEK specimen P is greater that that of CF/EPOXY SPECIMEN B. On the other hand, when the impacted side is in tension, the residual fatigue bending strength of CF/PEEK speicemen P is smaller than that of CF/EPOXY specimen B. In the case of impacted-side compression, fracture is proposed from the transverse crack generated near impact point. On the other hand, fracture is developed toward the impact point from the edge of interface-b delamination in the case of impacted-side tension.

• 대한기계학회논문집A
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• 제26권3호
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• pp.570-575
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• 2002

It is well-known that the bond strength between CFRP(Carbon Fiber Reinforced Plastic) and aluminum is significantly affected by the surface treatment of the CFRP and the aluminum. This study investigates the surface treatment of CFRP to improve the T-peel strength of CFRP/aluminum composites. The surface of %CFRP([0^0]_{14})$ was treated by the ion assisted reaction method under oxygen environment. T-peel strength tests were performed based on the procedure of ASTM D1876-95. The T-peel strength of surface-treated CFRP/aluminum composites was compared with that of untreated CFRP/aluminum composites. The results showed that the T-peel strength of surface-treated CFRP/aluminum composites was about 5.5 times higher than that of untreated CFRP/aluminum composites. SEM examination showed that the improvement of T-peel strength was attributed to the uniform spread and fracture of epoxy adhesive.

• 한국항공운항학회지
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• 제25권3호
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• pp.35-43
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• 2017

Research for solar-powered high altitude long endurance(HALE) UAV was conducted by Korea Aerospace Research Institute(KARI), and the EAV-3 with 19.5m wing span was developed. For HALE flight, aircraft should be lightly designed. Especially, airframe structure that accounts for a large portion of the total weight of aircraft should be lightweight. In this paper, development process of airframe structure for solar-powered HALE UAV, EAV-3, is described briefly. Domestic developed T-800 grade CFRP(Carbon Fiber Reinforced Plastic) composite material with high modulus and strength was used to design main load carrying structures. Flightloads analysis that takes into account large structural deformation was carried out. Stress and flutter analyses for airframe structure sizing were conducted. Static strength test for main wing and aircraft ground vibration test were conducted successfully and structural integrity was secured.