• Composites Research
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• v.24 no.1
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• pp.17-23
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• 2011

The failure of composite sandwich joints was experimentally investigated. A total of 30 joint specimens of 5 different types were tested with various fastening methods and core materials. In the NomexTM core sandwich joints, the core shear buckling was commonly observed in all the specimens which was followed by the slope change of the load-displacement curve. After the shear buckling, however, the joints carried additional loads of 50~200% over the buckling loads and then finally failed in the upper face breakage. The joints of PMI foam core showed the shear failure of the core instead of shear buckling and experienced the sharp drop of the carried load. Considering the failure modes, while both the core and face properties are important in the $Nomex^{TM}$ core joints, core shear strength seems to be the critical factor for the foam core joints.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.1
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• pp.115-126
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• 2001

In this paper, through a series of comparative experiments, effects of two different cure processing methods, cocure and precure, on the mechanical properties of honeycomb core materials for aircraft applications are considered. Mass of moisture accumulated into the closed cells of the sandwich panel specimen from the measured mass of moisture diffused to the full saturation state into the elements(skin, adhesive layer, Nomex honeycomb), consisting the honeycomb sandwich specimen has been calculated. Water reservoir of 70$\^{C}$ was used to have specimens absorb moisture to see the influence of moisture absorbed into sandwich panel on its mechanical properties. For the repair condition holding for 2 hours at 177$\^{C}$(350℉) temperature, a pressure due to the vapor expansion in each cell of the sandwich panel, which may result in the local separation of the interface between laminated skin and the surface of the honeycomb, has been estimated by vapor pressure-temperature relation from the thermodynamic steam table and compared to the pressure from the ideal gas state equation. The bonding strengths of the laminated skins on the flat surface of the Nomex honeycomb have been compared by the flatwise tension test and climbing drum peel test performed at room temperature for dry, wet and wet-repair specimens, respectively.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.1-4
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• 2004

In this paper we developed Composite-Smart-Structures(CSS) using sandwich structure composed of Glass/Epoxy laminates and Nomex honeycomb and microstrip antenna. Transmission/reflection theory shows that antenna performances can be improved due to multiple reflection by Glass/Epoxy facesheet, and honeycomb is used for air gap between antenna and facesheet. Stacked radiating patches are used for the wideband. Facesheet and honeycomb thicknesses are selected considering both wideband and high gain. Measured electrical performances show that CSS has wide bandwidth over $10\%$ and higher gain by 3.5dBi than initially designed antenna, and no doubt it has excellent mechanical performances by sandwich effect given by composite laminates and honeycomb core. The CSS concept can be extended to give a useful guide for manufacturers of structural body panels as well as antenna designers, promising innovative future communication technology.

• Composites Research
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• v.20 no.5
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• pp.26-33
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• 2007

Pull-out and shear strengths of insert Joints of sandwich structure were investigated by experiment. Specimens were prepared by cocuring of nomex honeycomb core and carbon-epoxy composite face using an adhesive FM73. A total of 75 specimens with 10 different types depending on the core height and density, face thickness, and loading direction were tested. In the test under pull-out loading, although both the core height and density affect the failure loads, the effect of cell density is more serious. Dominant factor fur failure loads of the joints under shear loading is face thickness and the effect of core height is negligible. In the joint with same dimension, failure loads vary depending on the potted area of the core, particularly in the pull-out test.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.74-77
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• 2001

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/$\textrm{m}^{3}$. 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 tile 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.

• Composites Research
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• v.14 no.6
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• pp.1-8
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• 2001

In this paper, the sandwich panel composites consisting of core material and face sheet were studied to evaluate the mechanical properties, noise level and fire resistance including flammability, smoke, and toxicity. Four types of sandwich panel were prepared using various kinds of panel and honeycomb materials. It was observed that Al honeycomb/Al skin composite materials had the excellent flatwise tensile strength and edgewise compressive strength compared with other types of composites. The flatwise compressive strength and flexural strength of Nomex honeycomb/Al skin composite were higher than those of other composites. PMI form/Al skin composite showed the higher core shear strength and facing bending strength. From the experimental results of flame resistance tests, it can be said that the phenol based skin composite has the excellent flame retardation properties, which are similar to those of the commercial skin composites.

• Journal of Aerospace System Engineering
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• v.4 no.1
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• pp.23-26
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• 2010

In this study, it was performed damage assesment of small scale composite aircraft developing. This aircraft adopted the sandwich structure to skin of wing. This study aims to investigate the residual strength of sandwich composites with Nomex honeycomb core and carbon fiber face sheets after the open hole damage by the experimental investigation. The 4-point bending tests were used to find the bending strength, and the open hole was applied to introduce the simulated damage on the specimen. The bending strength test results after open hole was compared with the results of no damaged specimen test. The FEM analysis is assessed via an experimental 4-point bending test.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.735-737
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• 2003

A superconducting motor consisting of high temperature superconducting (HTS) rotor and air-core stator is under development in Korea Electrotechnology Research Institute. HTS motor was designed for having the rated power of 100hp at 1800 rpm. HTS field winding is composed of sixteen HTS race track shaped coils wound with stainless steel-reinforced Bi-2223 tape conductor by react and wind fabrication method. Nomex Paper was used for electrical insulation. Each of four magnet pole assemblies was constructed with four double pancake sub-coils, mechanically stacked and electrically in series. Four magnet assemblies were fixed on an aluminum support structure to make effective heat transfer. Critical current (Ic) of HTS field winding was 41A but minimum Ic of sub-coils was 35A at 77K and self field. Joule heat generated in HTS field winding was 2.11W at 77K and 35A.

• Composites Research
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• v.30 no.2
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• pp.132-137
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• 2017

The purpose of this paper is to investigate failure characteristics of Carbon/BMI-Nomex honeycomb sandwich on design parameters. A total of 6 types sandwich specimens were manufactured according to core height, face thickness and density, and environmental condition were applied to evaluate temperature and humidity effects of one of these specimens. The test results show that the core shear buckling loads was commonly observed in all specimens except for the joint with density of $64kg/m^3$. After core shear buckling, however, the joint carried additional loads over the buckling loads and then finally failed in the upper face and lower face at the same time. In the case of specimen having high stiffness, the maximum failure load was low due to interfacial failure of the upper face and core without initial core shear buckling. The ETW1 and ETW2 conditions, which were carried out to evaluate the environmental condition of the sandwich specimen, show an initial failure mode which was significantly different from RTD condition. Also, the ETW2 condition with increased temperature under the same humidity shows that the core shear buckling load was 18% less than ETW1 condition.

• Composites Research
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• v.27 no.2
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• pp.77-81
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• 2014

In this study, it was performed damage assessment and repair of small scale aircraft adopted on composite. This aircraft adopted the sandwich structure to skin of wing. This study aims to investigate the residual strength of sandwich composites with nomex honeycomb core and carbon fiber face sheets after the open hole damage by the experimental investigation. The 4-point bending tests were used to find the bending strength, and the open hole was applied to introduce the simulated damage on the specimen. The bending strength test results after open hole were compared with the results of no damaged specimen test. In addition, The damaged composite structure was repaired using external patch repair method after removing damaged area. After that, this study presents comparison results of the experimental investigation between the damaged and the repaired specimen. It was found that the bending strength of repaired specimen was recovered up to 95% of undamaged specimen.