• Advances in aircraft and spacecraft science
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• v.2 no.3
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• pp.303-328
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• 2015

A design methodology is presented to develop the hingeless control surfaces for MAV using adhesively bonded Macro Fiber Composite (MFC) actuators. These actuators have got the capability to deflect the trailing edge surfaces of the wing to attain the required maneuverability, besides achieving the set aerodynamic trim condition. A scheme involving design, analysis, fabrication and testing procedure has been adopted to realize the trailing edge morphing mechanism. The stiffness distribution of the composite MAV wing is tailored such that the induced deflection by piezoelectric actuation is approximately optimized. Through ground testing, the proposed concept has been demonstrated on a typical MAV structure. Electromechanical analysis is performed to evaluate the actuator performance and subsequently aeroelastic and 2D CFD analyses are carried out to see the functional requirements of wing trailing edge surfaces to behave as elevons. Efforts have been made to obtain the performance comparison of conventional control surfaces (elevons) with morphing wing trailing edge surfaces. A significant improvement in lift to drag ratio is noticed with morphed wing configuration in comparison to conventional wing. Further, it has been shown that the morphed wing trailing edge surfaces can be deployed as elevons for aerodynamic trim applications.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.2
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• pp.138-145
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• 2009

Structural vibration and noise are hot issues in underwater vehicles such as submarines for their survivability. Therefore, active vibration and noise control of submarine, which can be modeled as hull structure, have been conducted by the use of piezoelectric materials. Traditional piezoelectric materials are too brittle and not suitable to curved geometry such as hull structures. Therefore, advanced anisotropic piezocomposite actuator named as Macro-Fiber Composite(MFC), which can provide great flexibility, large induced strain and directional actuating force is adopted for this research. In this study, dynamic model of the smart hull structure is established and active vibration control performance of the smart hull structure is evaluated using optimally placed MFC. Actuating performance of MFC is evaluated by finite element analysis and dynamic modeling of the smart hull structure is derived by finite element method considering underwater condition. In order to suppress the vibration of hull structure, Linear Quadratic Gaussian(LQG) algorithm is adopted. After then active vibration control performance of the proposed smart hull structure is evaluated with computer simulation and experimental investigation in underwater. Structural vibration of the hull structure is decreased effectively by applying proper control voltages to the MFC actuators.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.233-240
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• 2012

Hybrid SHCC is being researched actively for its excellent performance in controlling macro and micro cracks using macro and micro fibers, respectively. However, a significant autogenous shrinkage of SHCC is expected since it possesses high unit cement volume in its mix proportion, resulting in autogenous shrinkage cracks. Therefore, this study was performed to evaluate mechanical property of shrinkage-reducing type hybrid SHCC mixed together with steel fiber and PE fiber with excellent micro/macro crack controlling performance. In order to evaluate mechanical property of shrinkage-reducing type hybrid SHCC, replacement ratios of 0% and 10% of expansive admixture and water to binder ratios of 0.45, 0.3, and 0.2 were considered as variables. Then, shrinkage, compressive, flexural, and direct tensile tests were performed. The test results showed that mix proportion with W/B 0.3 significantly improved mechanical performance by using 10% replacement of expansive admixture.

• Journal of the Society of Disaster Information
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• v.10 no.1
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• pp.61-70
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• 2014

Synthetic fiber reinforced concrete is applicable to many applications for construction material. In general, synthetic fibers have low tensile strength and elastic modulus, but they have many advantages such as high crack resistance, impact resistance, chemical resistance, flexural behavior and corrosion free in fiber reinforced concrete. Recently, fiber reinforced concrete with macro synthetic fibers has been used to improve performance of structures in tunnel shotcrete, precast segmental lining and bridge slab and precast concrete structures. This study investigated the influence of bundled type polyamide fiber reinforced concrete on the flexural behavior in accordance with ASTM C 1609 and KS F 2566 standards.

• Journal of the Korean Wood Science and Technology
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• v.47 no.5
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• pp.617-632
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• 2019

This study aimed to investigate the anatomical structure and fiber quality of four lesser-used wood species namely Benuang (O. sumatrana), Duabanga (D. moluccana), Pisang Merah (H. hellwigii), and Terap (A. odoratissimus). This study evaluated its suitability for raw material in pulp and paper manufacturing. The anatomical structure was observed macro- and microscopically. Macroscopic structures were observed directly to the wood samples, while microscopic characteristics were observed through microtome specimens. Fiber dimension was measured through macerated specimens and fiber quality was analyzed following the Rachman and Siagian's method. Results showed that these four timber species have similarity in the indistinct growth ring, diffuse porous in a radial pattern, rounded solitary vessel outline, 1 to 3 cells of ray width, deposits within the rays, fiber length, and cell wall thickness. Differences were found on vessel diameter, vessel grouping, vessel frequency, tyloses existence, type of axial parenchyma, and ray height. Based on fiber length and its derived values, the wood fibers of all species studied are suitable for pulp and paper manufacturing. They belong to the II quality class. The produced pulp and paper would have good quality, especially in tensile, folding, and tear strength. To promote their utilization, silviculture aspect of these four species has to be well understood.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.644-647
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• 2004

Modulus of rupture (MOR) and flexural toughness in hybrid fiber reinforced cement pastes mixed with micro-fiber (carbon fiber) and macro-fiber (steel fiber) and replaced with silica fume according to the fixed ratio were researched. Reinforcing efficiency in specimens were estimated by two factors, such as strengthening factor $(F_s)$ and toughening factor $(F_t)$, which were calculated from the analysis of variance (ANOVA) of the response values, such as MOR and absorbtion energy $(W_0)$. According to the experimental design by the fractional orthogonal array, nine hybrid fibrous reinforced paste series and one non-reinforced control paste were manufactured. Specimens of each series were tested by the INSTRON Inc. 8502(model) equipment in three-points bending and then measured the load-deflection response relationships. Considerable strengthening of cement pastes resulted in' the case of other factors without carbon fiber and toughening of cement pastes about all factors showed high. Based on the significance of factors related to response values from ANOVA, following assessments were available; $F_s$ or MOR: silica fume $\gg$ steel fiber $\gg$ carbon fiber; $F_t\;or\;W_0$: steel fiber > carbon fiber > silica fume. Optimized composition condition was estimated by steel fiber of $1.5\%$, carbon fiber of $0.5\%$ and silica fume $7.5\%$ in side of strengthening and steel fiber of $1.5\%$, carbon fiber of $0.75\%$ and silica fume $7.5\%$ in side of toughening.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.651-658
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• 2010

Sixteen concrete mixes reinforced with hybrid steel-polybinyl alcohol (PVA) fibers and a control concrete mix with no fiber were tested in order to examine the effect of the micro and macro fibers on the slump and different mechanical properties of concrete. Main variables investigated were length and volume fraction of steel and PVA fibers. The measured mechanical properties of hybrid fiber reinforced concrete were analyzed using the fiber reinforcing index and compared with those recorded from monolithic steel or PVA fiber reinforced concrete. The initial slump of hybrid fiber reinforced concrete decreased with the increase of the aspect ratio and the volume fraction of fibers. In addition, splitting tensile strength, modui of rupture and elasticity, and flexural toughness index of concrete increased with the increase of the fiber reinforcement index. Modulus of rupture and flexural toughness index of hybrid fiber reinforced concrete were higher than those of monolithic fiber reinforced concrete, though the total volume fraction of hybrid fibers was lower than that of monolithic fiber. For enhancing the flexural toughness index of hybrid fiber reinforced concrete, using the steel fiber of 60 mm length was more effective than using the steel fibers combined with 60 mm and 30 mm lengths.

• Carbon letters
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• v.3 no.2
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• pp.85-92
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• 2002

4D carbon fiber preforms were manufactured by weaving method and their carbon fiber volume fractions were 50% and 60%. In order to form carbon matrix on the preform, coal tar pitch was used for matrix precursor and high density carbon/carbon composites were obtained by high densification process. In this process, manufacture of high density composites was more effective according to pressure increasement. When densificating the preform of 60% fiber volume fraction with 900 bar, density of the composites reached at 1.90 $g/cm^3$ after three times processing. Degree of pressure in the densification process controls macro pore but it can not affect micro pore. During the carbonization process, micro pore of the preform were filled fully by once or twice densification processing. But micro pore were not filled easily in the repeating process. Therefore, over three times densification processing is the filling micro pore.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.10
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• pp.1499-1507
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• 2017

This paper presents an impact-based piezoelectric vibration energy harvester using a freely movable metal sphere and a piezoceramic fiber-based MFC (Macro Fiber Composite) as piezoelectric cantilever. The free motion of the metal sphere, which impacts both ends of the cavity in an aluminum housing, generates power across a cantilever-type MFC beam in response to low frequency vibration such as human-body-induced motion. Impacting force of the spherical proof mass is transformed into the vibration of the piezoelectric cantilever indirectly via the aluminum housing. A proof-of-concept energy harvesting device has been fabricated and tested. Effect of the indirect impact-based system has been tested and compared with the direct impact-based counterpart. Maximum peak-to-peak open circuit voltage of 39.8V and average power of $598.9{\mu}W$ have been obtained at 3g acceleration at 18Hz. Long-term reliability of the fabricated device has been verified by cyclic testing. For the improvement of output performance and reliability, various devices have been tested and compared. Using device fabricated with anodized aluminum housing, maximum peak-to-peak open-circuit voltage of 34.4V and average power of $372.8{\mu}W$ have been obtained at 3g excitation at 20Hz. In terms of reliability, housing with 0.5mm-thick steel plate and anodized aluminum gave improved results with reduced power reduction during initial phase of the cyclic testing.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.1
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• pp.9-15
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• 2010

In this paper, dynamic modeling of hull structure including surface-bonded piezoelectric composite actuator was developed and structural vibration control performance was evaluated. Cylindrical shell structure with end-caps was considered as a host structure which could be used as a simple model of fuselage of aircraft and underwater vehicles. An advanced piezoelectric composite, macro-fiber composite(MFC), which has been developed in NASA Langley Research Center was applied for the effective structural vibration control. MFC has great flexibility by using piezoceramic fiber sheet and enhanced piezoelectric effect for in-plane motion by utilizing interdigitated electrode. Governing Equations were derived from the finite element model and modal characteristics were investigated. Modal test was conducted to verify the finite element model. Optimal controller was designed and implemented for the evaluation of vibration control performance. Structural vibration was controlled effectively by applying proper control input to the piezoelectric actuators.