해외 기술동향

황운봉 ( Hwang Un Bong ) 한국복합재료학회 2003 Composites research Vol.16 No.6

원공조치를 가진 탄소섬유강화 플라스틱 적층판의 피로수명에측

허재석,황운봉,박현철,한경섭,Heo, Jae-Seok,Hwang, Un-Bong,Park, Hyeon-Cheol,Han, Gyeong-Seop 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.3

Fatigue life prediction and fatigue behavior of circular notched carbon fiber reinforced plastic laminates are presented. Point and average stress criteria by Whitney and Nuismer are generalized to fatigue fracture criteria for notched laminates. Residual strength degradation model and the assumptions on the stress redistribution are introduced during the derivation of prediction equations. S-N curve, Basquin's relation, and H and H's FLPE1 are chosen for evaluation of residual strength of unnotched laminates and six prediction equations are derived. Experiments are performed using Graphite/Epoxy laminates whose fiber orientation is $[0$^\circ$/+45$^\circ$/-45$^\circ$/90$^\circ$]s. Presented prediction equations are reasonably close to experimental data and proposed appoach is found to be suitable to predict fatigue life of notched composite laminates.

강도를 고려한 원통형 복합재료 구조물의 최적설계

김창완,황운봉,박현철,신대식,박의동,Kim, Chang-Wan,Hwang, Un-Bong,Park, Hyeon-Cheol,Shin, Dae-Sik,Park, Ui-Dong 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.3

An optimization procedure is proposed for the design of cylindrically laminated composite shell having midplane symmetry and subjected to axial force, torsion and internal pressure. Tsai-Wu and Tsai-Hill failure criteria are taken as objective functions. The stacking sequence represents the design variable. The optimal design formulation based on state space method is adopted and solution proccedure is described with the emphasis on the method of calculations of the design sensitivities. A gradient projection algorithm is employed for the optimization process. Numerical results are presented for the several test problems.

축 방향 하중 전달 부재의 진동제어

최승주,박현철,황운봉,Choe, Seung-Ju,Park, Hyeon-Cheol,Hwang, Un-Bong 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.12

An active control of the vibration transmitted by longitudinal load in flight control system is investigated numerically. The flight control system is modeled as a finite, thin shell cylinder with constant thickness. A vibration source is generated by exterior monopole source. Distributed piezoelectric actuator is used to control of the vibration. Thin shell theory is used to formulate the numerical models. The amplitude of vibration at discrete location and power transmission are minimized by analytical optimization method. Genetic algorithm is used as numerical optimization method to search optimal actuator position and size which amplitude of vibration is minimized.

원통형 밀폐공간 내부의 능동소음제어

이호준,박현철,황운봉,Lee, Ho-Jun,Park, Hyeon-Cheol,Hwang, Un-Bong 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.9

An active control of the transmission of noise through an aircraft fuselage is investigated numerically. A cylinder-cavity system was used as a model for this study. The fuselage is modeled as a fi nite, thin shel cylinder with constant thickness. The sound field generated by an exterior monopole source is transmitted into the cavity through the cylinder. Point force actuators on the cylinder are driven by error sensor that is placed in 3D cavity. Modal coupling theory is used to formulate the numerical models and describe the system behavior. Minimization of the acoustic potential energy in the fuselage is carried out as a performance index. Continuous parameter genetic algorithm is used to search the optimal actuator position and both results are compared.

압전작동기를 이용한 트러스 구조물의 다중 모드 진동제어

주형달,박현철,황운봉,Ju, Hyeong-Dal,Park, Hyeon-Cheol,Hwang, Un-Bong 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.10

Truss structures are widely used in many space structures, such as large antenna systems, space stations, precision segmented telescopes because they are light in weight and amenable in assembly or deployment. But, due to the low damping capacity, they remain excited for a long time once disturbed. These structural vibrations can reduce life of the structures and cause unstable dynamic characteristics. In this research, vibration suppression experiment has carried out with a three-dimensional 15-member truss structure using two piezoelectric actuators. Piezoelectric actuators which consist of stacks of thin piezoelectric material disks are directly inserted to the truss structure collocated with the strain sensors. Each actuator is controlled digitally in decentralized manner, based on local integral and proportional feedback. The optimal positions of the actuators are determined by the modal damping ratio and the control force. Numerical simulation has carried out to determine optimal position of each actuator.

스마트 스킨 구조물 시편의 유한요소 해석

전지훈 ( Jeon Ji Hun ),황운봉 ( Hwang Un Bong ) 한국복합재료학회 2003 Composites research Vol.16 No.4

샌드위치 구조물의 응용된 형태인 스마트 스킨 구조물을 ABAQUS로 유한요소 해석하였다. 심재로 쓰이는 하니컴은 일반적으로 두께 방향 강성 및 전단 강성만 제작회사에 의하여 제공된다. 이를 바탕으로 하니컴 재료의 물성을 추정하여 다른 방향의 제공되지 않는 물성을 계산하였고, 이를 유한요소 해석시 물성 자료로 적용하였다. 또한, 스마트 스킨 구조물의 좌굴 및 3점 굽힘 거동을 유한요소 해석하였으며, 기존의 실험결과 및 이론값과 비교 분석하였다. 비교적 결과가 잘 일치하였다. 본 연구를 통하여서 하니컴의 물성을 사용 패키지에 적용하는 방법 및 타당한 근거를 제시하였고, 이 결과를 바탕으로 스마트 스킨 구조물을 상용 패키지로 유한요소 해석시 지침을 제시할 수 있다. FEM analysis of the smart skin structure, and application of the sandwich structures investigated. The honeycomb manufactures only provide stiffness of thickness direction and transverse shear modulus. Although these are dominant mechanical properties, the other mechanical properties are needed in FEM analysis. Hence, this work shows procedures of obtaining those mechanical properties. Honeycomb material was assumed to be an isotropic material and properties are estimated by its dominant honeycomb properties. The other honeycomb properties are then obtained by mechanical properties of Nomex. Buckling test and three point bending test were simulated by ABAQUS. Both the shell and solid element models were used. The results were compared with experimental results and analytical approaches. They showed good agreements. This study shows a guideline of FEM analysis of smart skin structure using commercial a FEM package.

표면 손상을 입은 적충판의 강도 예측 및 분석

최덕현 ( Choe Deog Hyeon ),황운봉 ( Hwang Un Bong ) 한국복합재료학회 2003 Composites research Vol.16 No.5

본 논문에서는 표면 손상을 입은 적충판의 파괴 강도를 결함이 없는 적충판의 파괴 강도와 결함이 있는 적충판의 파괴 강도를 이용하여 예측하였다. 이를 위해 고전 적충판 이론을 적용하여 적충판의 파괴 강도식을 단순화했으며 이를 표면 손상을 입은 적충판에 적용하였다. 단순화한 적충판의 파괴 강도 이론식의 검증을 위해 Lagace와 Tsai의 논문에서 측정한 데이터를 이용하였다. 또한 표면 손상을 입은 적충판의 파괴 강도 예측식의 검증을 위해 실험을 수행하였다. 실험을 위해 표면 결함이 없는 적충판과 표면 결함이 있는 적충판을 제작하여 실험하였으며 이 결과를 예측식과 비교하였다. 시편의 섬유 방향은 인장 방향과 같은 방향으로 제작되었으며, 예측식과 실험 결과는 잘 일치하였다. 따라서 본 논문에서 예측한 표면 결함이 있는 적충판의 파괴 강도 예측식을 이용하여 복합재료가 사용되는 구조물이 표면손상이 되었을 때 이 구조물의 파괴 강도를 예측할 수 있을 것이다. In this paper, the fracture strength of the surface damaged laminates was predicted by applying the fracture strengths of the unflawed and flawed laminates. For prediction, the theoretical equation about the fracture strength of laminates was simplified applying classical laminate theory and was applied to the surface damaged laminates. Lagace`s and Tsai`s experimental data were used for verifying the theoretical equation. Moreover, to verify the theoretical prediction, an experiment was performed. Surface unflawed laminate and flawed laminates were fabricated and the experiments were made and these results were compared with theoretical predictions. The specimens` fiber direction was same to the tensile direction and the theoretical predictions and the experimental results were showed good agreement. Therefore, by this equation, the fracture strength of structures made of composites will be able to be predicted when the surface of the structures was damaged.

압전감지기/작동기를 이용한 복합적층판의 다중모드 진동제어

김문현,강영규,박현철,황운봉,한경섭,Kim, Mun-Hyeon,Gang, Yeong-Gyu,Park, Hyeon-Cheol,Hwang, Un-Bong,Han, Gyeong-Seop 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.10

Multi-model vibration control of laminated composites plates for various fiver orientations has been carried out by making use of piezolectric materials(PZT) as sensors and actuators. Cantilever plate is used as a specimen to test multi-modal vibration supression under random exitation. Impulse technique is applied to determine the natural frequency, the damping ratio(.zeta.) and the modal damping(2.zeta..omega.) of the first bending and the trosion modes. Two independent controllers are implemented to control the two modes simultaneously and established digitally on the basis of the direct negative velocity feedback control with collocated sensor/actuator. Experimental results for various fiber orientations and feedback gains are compared with finite element analysis considering stiffnesses and dampings of piezoeletiric sensors, actuators and bonding layer.

통신 안테나용 허니콤 샌드위치 구조물의 충격 손상에 관한 연구

김차겸,이라미,박현철,황운봉,박위상,Kim, Cha-Gyeom,Lee, Ra-Mi,Park, Hyeon-Cheol,Hwang, Un-Bong,Park, Wi-Sang 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.2

The impact response and damage of CLAS panel was investigated experimentally. The facesheet material used was RO4003 woven-glass hydrocarbon/ceramic and the core material was Nomex honeycomb with a cell size of 3.2mm and a density of 96 kg/㎥. The shield plane used was RO4003 and 2024-T3 aluminum. Static indentation and impact test was conducted to characterize the type and extent of the damage observed in two CLAS panels, and the performance of antenna used in a wireless LAN system. Correlation of peak contact force, residual indentation and the delamination area shows impact damage of the panel with an aluminum shield plane is larger than that of the panel with RO4003 shield plane, although the former is more penetration resistant. The damage was observed by naked eye, ultrasonic inspection and cross sectioning. The shape and size of delamination was estimated by ultrasonic inspection, and the area of delamination linearly increases as impact energy increases. The performance of impact damaged antenna was estimated by measuring return loss and radiation pattern. It was revealed that the performance of antenna was related to the impact damage and there was a threshold that the performance of antenna fell as impact energy level changed. The threshold was between the impact energies of 1.5J and 1.75J.