• International Journal of Highway Engineering
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• v.12 no.4
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• pp.175-186
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• 2010

When a rigid post is exposed to traffic, it is hazardous not only to head-on impacts but also to side impacts. Clip-type slip base is an effective measure to reduce the severity of head-on impacts and side impacts as well because of its multi-directional release mechanism. Side impact tests were conducted and the results were analysed to demonstrate the hazardousness of a rigid post to a side impact and the crash worthiness of a post having clip-type slip base. For that, side impact test standard was made adapting the NCHRP Report 350, and 820kg-50km/h side impact tests were made for posts of D101.6mm(t=4.2mm) with and without slip base. Additionally, 35km/h side impact to the same post with slip base was conducted to check whether the clip-type slip base release mechanism works properly to the low impact speed. The tests revealed that the rigidly connected post was very hazardous to side impact while the post with the clip-type slip base reduced the impact severity tremendously.

• Composites Research
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• v.13 no.1
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• pp.40-49
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• 2000

The objective of this research is to develop the impact monitoring techniques providing impact identification and damage diagnostics of smart composite laminates susceptible to impacts. This can be implemented simultaneously by using the acoustic waves by the impact loads and the acoustic emission waves from damage. In the previous research, we have discussed the impact location detection process in which impact generated acoustic waves are detected by PZT using the improved neural network paradigm. This paper describes the implementation of time-frequency analysis such as the Short-Time Fourier Transform (STFT) and the Wavelet Transform (WT) on the determination of the occurrence and the estimation of damage.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.340-343
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• 2011

Explosive bolts are reliable and efficient mechanical fastening devices having the special feature of a built-in release. The disadvantage of explosive bolt lies in that it is based on the high explosive effect of a pyrotechnic charge. The aim of the present work is to propose a pyrotechnically releasable mechanical linking device for two mechanical elements that does not suffer from such drawbacks. The pyro-lock using the pressure cartridge has the release characteristic without fragmentation and minimum pyro-shock. The present work is focused on the design, the interpretation of structure, the separation mechanism, separation force, and the results of various tests.

• Magazine of RCR
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• v.4 no.2
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• pp.50-52
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.74-74
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• 2004

탄소섬유강화 적층재(Carbon Fiber Reinforced Plastic, 이하 CFRP)는 강성도는 뛰어나지만 충격특성에는 취약한 단점이 있다. 따라서 충격저항과 충격에너지 흡수율이 상대적으로 우수한 유리섬유강화 적층재(Glass Fiber Reinforced Plastic, GFRP) 및 아라미드섬유강화 적층재(Aramid Fbier Reinforced Plastic, 이하 AFRP)를 CFRP 적용분야에 대체하고 점차적으로 피로특성을 개선시켜 나간다면 특성이 더욱 개선된 제품을 사용할 수 있을 것으로 판단된다.(중략)

• Polymer(Korea)
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• v.26 no.2
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• pp.270-278
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• 2002

In this study, the fracture behavior by low velocity impact damage and the tendencies of impact energy absorption were investigated. Low velocity impact tests were performed using a mini tower drop weight impact tester, and graphite powder, carbon black and milled carton fiber were chosen as additives. Addition of graphite powder increased the maximum load and maintained the stress long until the total penetration happened. At the content of 9 vol%, they showed the maximum of 42% improvement in impact strength compared composites containing no additives. At the test with low impact energy of 0.4 J, impact energy was consumed by delamination in the composite containing no additives, however, as graphite contents increased, the tendency of failure changed to the penetration of the specimen.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.208-211
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• 2007

Separation Devices have two functions. These two functions are to bond and to separate two bodies. This paper is about separation devices which use explosives to separate their bodies. Explosive bolt is separated with two bodies when the explosives in the body detonated. The good things of explosive bolt are that it has simple operational system and it is made of few parts. But it has side effects; fragment and pyre-shock. To avoid these side effects gas expansion separation(GES) bolt and pressure cartridge actuation separation(PAS) devices are invented. These use pressure to separate their bodies. The pressure is generated when explosives are burned. But the sizes of PAS devices are bigger than explosive bolts. And GES bolt has a mechanically lower bonding ability than that of explosive bolt. When you design separation devices, it is recommended to know operational system and characteristics of separation devices, to design best one.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.22-28
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• 2010

To detect the damage in composite structure, nondestructive evaluation techniques are widely used. Tapping test is perhaps the most common technique used for the detection of damage in composite laminates. The method is accomplished by tapping the inspection area with light hammer-like device. The tapping test has the ability that indicates damages in a structure due to a localized change of stiffness. The change in vibration signature may be detected by measurement of the dynamic contact force during impact. In this study, it has been shown that the characteristics of impact force histories from a structure during tapping are changed by the presence of damage such as surface crack and delamination. And impact response analysis has been performed on composite rotor blade with crack to investigate the effect of damage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.23-31
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• 2018

Recently, there was an collision accident of vehicle-concrete median barrier and unfortunately, passengers were killed by exceeded capacity of concrete median. Therefore, improving the capacity of concrete median barrier is need to reduce damage. Accordingly, in this study, appropriate collision model verified by using the FE analysis program LS-Dyna and recommend a concrete median barrier section. The improvement parameters such as wire mesh diameter, steel plate, rubber pad were selected for improved capacity of the median barrier. Finally, section of concrete median barrier improved wire mesh diameter decreased volume loss, section of concrete median barrier improved rubber pad accepted impact loading and increased elastic area.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.18-25
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• 2005

This paper describes a supersonic separation of air-launching rocket from the mother plane. Three dimensional Euler equations were numerically solved to analyze steady/unsteady state fluid flows. The results of simulation clearly demonstrate effect of shock-expansion wave interaction between the rocket and the mother plane. Moreover, important influential factors at separating stage of the rocket were extracted with a comprehensive analysis. Finally, from the consideration of supersonic-separation, a guideline to safety-separation is given to the design of supersonic air-launching rocket.