• Composites Research
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• v.17 no.3
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• pp.15-22
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• 2004

Acoustic load generated by rocket propulsion system is one of major dynamic loads during lift-off phase so that it causes the structural failure and electronic malfunction of payloads. Acoustic loads can be greatly reduced by an appropriate acoustical design of nose faring structures. This paper deals with the acoustical design of the nose fairing structure for launch vehicle. It is well known that a honeycomb sandwich structure is a poor sound insulator because of its high specific stiffness. In this paper, the sound transmission characteristics of four kinds of honeycomb structures for noise fairing were investigated by means of numerical and experimental ways. In order to estimate transmission loss, infinite plate theory by Moore and Lyon and statistical energy analysis (SEA) method were used. The predicted results showed a good agreement with measured ones. These enabled us to determine a proper core material for nose fairing, which shows good sound insulation performance per weight.

• 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.17 no.6
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• pp.22-27
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• 2004

The objective of this work is to design Surface Antenna Structure (SAS) and investigate fatigue behavior of SAS that is asymmetric sandwich structure. This term, SAS, indicates that structural surface becomes antenna. Constituent materials are selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, SSSFIP elements inserted into structural layers were designed fur satellite communication at a resonant frequency of 12.5 GHz and final demonstration article was $16{\;}{\tiems}{\;}8$ array antenna. From electrical measurements, it was shown that antenna performances were in good agreement with design requirements. In cyclic 4-point bending, flexure behavior was investigated by static and fatigue test. Fatigue life curve of SAS was obtained. The fatigue load was determined experimentally at a 0.75 (1.875kN) load level, Experimental results were compared with single load level fatigue life prediction equations (SFLPE) and in good agreement with SFLPE. SAS concept is the first serious attempt at integration fur both antenna and composite engineers and promises innovative future communication technology.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.9
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• pp.862-868
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• 2010

Development of a small scale aircraft has been carried out for the BASA(Bilateral Aviation Safety Agreement) program in Korea. This aircraft adopted all the composite structures for environmental friendly by low fuel consumption due to its lightness behavior. However the composite structure has s disadvantage which is very weak against impact due to foreign object damages. Therefore the aim of this study is focusing on the damage evaluation and repair techniques of the aircraft composite structure. The damages of composite laminates including the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate were simulated by a drop weight type impact test equipment and the damaged specimen were repaired using the external patch repair method after removing damaged area. The compressive strength test and analysis results after repairing the impact damaged specimens were compared with the compressive strength test and analysis results of undamaged specimens and impact damaged specimens. Finally, the strength recovery capability by repairing were investigated.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.56-64
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• 2002

In this work, a smart skin of multi-layer structure is designed and manufactured. Through the compression test, the characteristic of smart skin behavior was examined. We have predicted stress of each layer and the first failed layer of the smart skin structure by using MSC/NASTRAN. The finite element model was verified by comparing measured data from the compression test and result from the geometrically linear/non-linear analysis. The finite element model was used for obtaining design data from the parametric study. It was confirmed that shear moduli of honeycomb core affect the buckling load of smart skin where shear deformation was considerable.