• Journal of Electrical Engineering and Technology
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• v.9 no.4
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• pp.1349-1354
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• 2014

This paper presents a compact and portable high-voltage generator based on magnetic-core Tesla transformer for driving an UWB high power electromagnetic source. In order to optimize the performance of the high-voltage generator, a novel open-loop cylindrical magnetic-core adopting the quad-division lamination structure is proposed and manufactured. The designed high-voltage generator using the proposed magnetic core has a battery-powered operation and compact size of $280mm{\times}150mm$ in length and diameter, respectively. The high-voltage generator can produce a voltage pulse waveform with peak amplitude of 450 kV, a rise time of 1.5 ns, and pulse duration of 2.5 ns at the 800 V input voltage.

• Journal of the Korean Wood Science and Technology
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• v.51 no.1
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• pp.14-22
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• 2023

Economical use of larix (larch) boards (grade 3) in industries is lower than that of imported hardwood; thus, studies have been conducted toward performance improvement of larix boards. Herein, flexural modulus of larix board samples laminated with wood adhesives polyurethane resins, poly (vinyl acetate) resins, phenol-resorcinol-formaldehyde resins, melamine-formaldehyde resins, and urea-formaldehyde resins was compared with that of the samples bonded with adhesives reinforced with mesh-type basalt fibers. Moreover, the flexural moduli of the laminated samples bonded by mesh-type basalt fibers were compared with those of reinforced samples. The results showed that boards laminated with polyurethane and urea-formaldehyde resin adhesives had higher flexural modulus than those without the lamination. In particular, the increase in the flexural modulus was relatively significant for the 2- and 3-ply board structures laminated with polyurethane adhesives compared to those with reinforcement. The 3-ply board structure without reinforcement had the highest flexural modulus when the urea-formaldehyde resin adhesive was used.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.444-449
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• 1998

A modal transducer in two-dimensional structure can be implemented by varying the distributed transducer's gain spatially. In this paper, a method based on finite element method is developed for optimizing spatial gain distribution of PVDF transducer to create the modal transducer for specific modes. Using this concept, one can design the modal transducer in two-dimensional structure having arbitrary geometry and boundary conditions. As a practical means for implementing this continuous gain distribution without repoling die PVDF film, the gain distribution is approximated by optimizing gain-weights of interface circuit. The whole spatial area of the PVDF film is divided into several electrode segments and the signals from each segment are properly weighted and summed by interface circuit. This corresponds to the approximation of a continuous function using discrete values. The electrode partition is optimized using the genetic algorithm. Gain-weights are optimized using the simplex search method. A modal sensor for first to fourth modes of aluminum plate is designed using PVDF film with gain-weighted interface circuit. Various lamination angles of PVDF film are taken into consideration to utilize the anisotropy of the PVDF film. Performance of the optimized' PVDF sensor is demonstrated by numerical simulations..

• Steel and Composite Structures
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• v.28 no.5
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• pp.629-639
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• 2018

In this paper, the vibroacoustic responses of baffled laminated composite sandwich flat panel structure under the influence of harmonic excitation are studied numerically using a novel higher-order coupled finite-boundary element model. A numerical scheme for the vibrating plate has been developed in the frame work of the higher-order mid-plane kinematics and the eigen frequencies are obtained by employing suitable finite element steps. The acoustic responses are then computed by solving the Helmholtz wave equation using boundary element method coupled with the structural finite elements. The proposed scheme has been implemented via an own MATLAB base code to compute the desired responses. The validity of the present model is established from the conformance of the current natural frequencies and the radiated sound power with the available benchmark solutions. The model is further utilized to scrutinize the influence of core-to-face thickness ratio, modular ratio, lamination scheme and the support condition on the sound radiation characteristics of the vibrating sandwich flats panel. It can be concluded that the present scheme is not only accurate but also efficient and simple in providing solutions of the coupled vibroacoustic response of laminated composite sandwich plates.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.41-48
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• 2014

Direct writing(DW) is a method of patterning materials to a substrate directly, without a mask. It can use a variety of materials and be applied to various fields. Among DW systems, the flow-based type, using a syringe pump and nozzle, is simpler than other types. Furthermore, the range of materials is exceptionally wide. In additive processes, a three dimensional structure is made of stacking layer. Each layer is made of several lines. In this regard, good surface roughness of fabricated layers is essential to three dimensional fabrication. The surface roughness of any fabricated layer tends to change with the dispensing pattern. When multiple layers fabricated by a nozzle dispensing system are stacked, control of the nozzle position from the substrate is important in order to avoid interference between the nozzle and the fabricated layer. In this study, a fluid direct writing system for three dimensional structure fabrication was developed. Experimentsto control the position of the nozzle from substrate were conducted in order to examine the characteristics of the material used in this system.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.363-369
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• 2001

By alternating $Al_{18}B_4O_{33}$/AC4CH composites with Al1050 sheets and then hot pressing, MMC/Al laminate composites have been successfully fabricated as parameters of the laminate structure and the number of Al sheet. Impact properties for laminate composites have been evaluated both in the laminate structure and in the impact load direction. Lamination of Al sheet and MMC layer showed a remarkable improvement in the absorbed impact energy compared to that of monolithic MMC. Laminate composites mounted with Al sheet at the outside of the configuration had a higher impact energy in the edge wise compared to that with Al sheet at the inside. Furthermore, there was an anisotrpy in the impact value of laminate composites, that is, impact values for the flat wise in a constant volume fraction of Al sheet dramatically increased along with Al sheet number, even if impact values fur the edge wise were nearly constant.

• Transactions on Electrical and Electronic Materials
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• v.13 no.1
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• pp.23-26
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• 2012

A zero-shrinkage sintering process in which the shrinkage of x-y axis is controlled to be zero is in great demand due to the trend of high integration in the ceramic modules. Among the zero-shrinkage sintering processes that are available, the proposed glass infiltration method where the viscous but fluidic glass infiltrates of the $Al_2O_3$ particles in the structure of $Al_2O_3$/glass/$Al_2O_3$ during firing is one of the applicable methods. However, the above proposed glass infiltration method has the problem of the warpage-like delamination. This occurred at the outermost surface of the multiple-bundle substrate. It is thought that the decomposed gas rapidly expands in low viscous glass to create vacant space. To solve this problem, the vacant space was tamped with $Al_2O_3$ particles to lead to the actual improvement of the sintered properties. With 15 wt% of tamping $Al_2O_3$ particles in glass, most of the vacant space disappeared. Fully densified zero-shrinkage substrate without delamination can be obtained.

• Composites Research
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• v.32 no.2
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• pp.108-112
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• 2019

There has been a continuous study on the weight reduction of structure by composites. Unlike isotropic materials, the physical properties of composites vary according to the direction of laminate and the order of lamination. Therefore, in the case of composite ladders, it is essential to perform structural analysis to verify the planned design. In this study, ladder was designed by applying fabric material. In addition, the effect of loading position on the ladder was analyzed through finite element analysis, and structural performance was analyzed by selecting the most problematic location. We analyzed the effect of stacking order on the structural strength of the ladder by analyzing the structure by applying various stacking sequence and measuring the failure value in each layer.

• Journal of the Korean Society of Safety
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• v.29 no.6
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• pp.9-14
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• 2014

Recently many efforts and researches have been done to cope with industrial facilities that require a low energy machines due to the gradual depletion of the natural resources. The fiber-reinforced composite materials in general have good properties and have the proper mechanical properties according to the change of the ply sequences and fiber distribution types. However, in the fiber-reinforced composite material, there are several problems, including fiber breaking, peeling, layer lamination, fiber cracking that can not be seen from the metallic material. Particularly, the fracture and delamination are likely to be affected by the thickness of the stacking laminates when the bi-material laminated structure is subjected to a load of the mixed mode. In this study, we investigated the effect of the thickness ratio of the difference in the CFRP/GFRP bi-material laminate composites by measuring the cracking behavior and the AE characteristics in a mixed mode loading, which may be generated in the actual structure. The results show that the thickness of the CFRP becomes more thick, the mode I energy release rate becomes a larger, and also the influence of mode I is greater than that of mode II. In addition, AE amplitude which shows the level of the damage in the structure was obtained the more damage in the CFRP with the thin thickness.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.126-129
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• 2001

LIPCA (LIghtweight Piezo-composite Curved Actuator) is an actuator device which is lighter than other conventional piezoelectric ceramic type actuator. LIPCA is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. LIPCA has curved shape like a typical THUNDER (thin-layer composite unimorph feroelectric driver and sensor), but it is lighter an than THUNDER. Since the curved shape of LIPCA is from the thermal deformation during the manufacturing process of unsymmetrically laminated lay-up structure, an analysis for the thermal deformation and residual stresses induced during the manufacturing process is very important for an optimal design to increase the performance of LIPCA. To investigate the thermal deformation behavior and the induced residual stresses of LIPCA at room temperature, the curvatures of LIPCA were measured and compared with those predicted from the analysis using the classical lamination theory. A methodology is being studied to find an optimal stacking sequence and geometry of LIPCA to have larger specific actuating displacement and higher force. The residual stresses induced during the cooling process of the piezo-composite actuators have been calculated. A lay-up geometry for the PZT ceramic layer to have compression stress in the geometrical principal direction has been designed.