• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.55-62
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• 2015

The electromagnetic force induced by an intense electric current pulse, which generates an electromagnetic field around the metal jet originating from a shaped charge, can disperse and scatter the high-speed metal jet. An electric device consisting of an RLC circuit applies an intense electric current pulse that flows in the circuit while the metal jet passes between two electrodes. In this study, the metal jet formation was simulated using the ALE technique in 2-D, and a 3-D finite element model was mapped using 2-D simulation results to induce the electric current directly. The deformed shapes of the metal jet and the electromagnetic force were calculated using a finite element analysis by inducing the electric current directly, and the major parameters of the intense electric current pulse for breaking up the metal jet were examined.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.121-131
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• 2005

For thrust motion of high speed underwater torpedo the special hydro reactive fuels that burns in vapor water and water supply from aboard is used. The main component of this hydro reactive fuel is the powder of active metal (Mg, Al) that can burn in water vapor with large heat generation in the rocket combustion chamber. The thermodynamic analysis of combustion properties of the burning of the particles of these active metal in the vapor water have been carried out. The conception for the possible content variants of the hydro reactive fuels have been discussed using the geometrical and thermodynamic combustion conditions with the basic recommendation for contents of designed hydro reactive fuels in future.

• Explosives and Blasting
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• v.36 no.2
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• pp.10-18
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• 2018

The shaped charge is used in explosive demolition of steel frame structure, but it was often not used because it was limited to use or impossible to supply at domestic and foreign. To solve this problem, we needed a device that could generate matal jets using industrial explosive. In this study, we made a charging container, which metal jets were generated when explosives were detonated. Cutting performance tests were carried out to evaluate the effect of cutting of a charging container on a steel plate of 25mm thickness. In addition, we compared the results between the numerical simulation of penetration process and cutting performance tests and then was evaluated a cutting performance for steel plates of 35mm and 70mm thickness.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.5
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• pp.577-584
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• 2014

In this study, the behavior of a shaped charge projectile's metal jet was analyzed using flash radiography. The projectile was installed horizontally to observe the behavior of jet for enough time. While the X-ray tube heads are fixed at one point, the behavior range of the jet is wide in this experimental set up, therefore the angle between the X-ray tube heads and the jet tip is changed continuously as jet moves forward. Jet particle's locations calculated from the X-ray films become different from their real positions under this situation because of the film to object distance(FTOD) and correction for error by FTOD is required. In this study, a method was devised to correct the error by FTOD and this was applied for the investigation of jet behavior of a 70 mm caliber's shaped charge.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.1
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• pp.26-32
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• 2014

In this study, DC (Direct current) type steam plasma igniter is developed for effective ignition of high-energy density metal aluminum and gas temperature is measured by emission spectrum of OH radical. Because of the ultra-high gas temperature, the DC plasma jet is measured by Boltzmann plot method which is the non-contact optical technique and spectrum comparison-analysis. And both methods were applied to experiment after accurate verification. As a result, we could identify that plasma jet temperature is 2900 K ~ 5800 K in the 30 mm range from the nozzle tip.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.3028-3044
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• 1993

A metallic bond of great strength for the same or dissimilar metals can be produced by the explosive welding. The formation of a metallic jet at the interface between the two impacting plates has been simulated using the numerical hydrocode DYNA2D. The mechanism of explosive welding for the wave formation is also analyzed by the computer simulation technique. The microscopic with the experimentally observed behaviour of the explosive welding. The computer simulations of the explosive welding process have proven especially useful for analyzing the mechanism of metallic bones.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.6
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• pp.9-15
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• 2012

As a propellant of a high speed underwater vehicle, the hydro-reactive solid metal particles using seawater as a oxidizer maximizes its specific impulse when the solid metal particles and the seawater are uniformly mixed in the combustion chamber. The purpose of this study is to investigate the effects of injector geometry on the particle distribution of similarity point of view. For the purpose of this similarity of the mean velocity and particle number density along the radial direction was measured by Particle Image Velocimetry(PIV).

• Journal of the KSME
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• v.32 no.7
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• pp.604-612
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• 1992

D-Gun과 plasma 코팅이라고 하는 코팅(도금) 기술은 1950년대 미국 유니온 카바이드사에 의해 세계 최초로 개발되어 실용화된 이래 전세계의 산업전반에 걸쳐 꾸준히 그 응용분야가 확대되어 왔으며, 오늘날에는 점보 제트 여객기의 엔진으로부터 석유화학설비, 제철제강설비, 섬유기계, 인쇄기계, 제지기계, 식품기계, 발전설비, 자동화부품, 전자제품 등에 이르기까지 각종 산업기계 및 제품 생산에 응용되고 있다. 특히 최근에는 이들 산업기계가 고속화, 고성능화, 고품질화됨에 따라 그 구성부품도 필연적으로 고성능의 내구성 등이 요구되어 세라믹 등 특수 코팅의 필요성이 절실히 요구되고 있다.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.72-82
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• 2017

Nozzleless booster is one of the applicable components for integral rocket ramjet (IRR). In order to predict nozzleless solid booster performance, the simplified theoretical analysis was applied for L/D=5, 6, 7, 9, 11, and 13. Al-HTPB and Zr-HTPB propellant with a high metal content were used to increase the hardness because of the combustion gas flow effect. It was found that the trends between the simplified theoretical analysis and experiments were similar.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.84-92
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• 2010

현재 가동 중인 몇몇 가압 경수로 원전 안전 1등급 설비의 이종금속 용접부는 일차수응력부식균열(PWSCC : Primary Stress Corrosion Cracking) 발생의 세가지 조건(민감 재질, 부식 환경, 인장응력)을 동시에 충족하고 있다. 즉, 이종금속 용접부는 PWSCC에 민감한 재질인 Alloy 600 계열 합금으로 제작 또는 용접되어 있으며 고온 수화학 부식 환경 하에 놓여있다. 아울러 오스테나이트 스테인리스 강의 예민화 예방을 위한 용접 후열처리 미실시로 높은 인장 용접 잔류응력이 작용하고 있다. 이러한 이종금속 용접부의 특성상 PWSCC가 발생할 잠재성이 있을 뿐만 아니라 국내외적으로 Alloy 600 계열 합금으로 제작 및 용접된 가압 경수로 원전 안전 1등급 설비의 이종금속 용접부에 실제 PWSCC가 발생된 사례들이 다수 보고되고 있다. 운전 환경 및 재질 변화 없이 PWSCC 발생을 예방하기 위해서는 인장 잔류응력을 이완시켜 낮은 인장 또는 압축 응력화하여야 한다. 이러한 인장 잔류응력 이완방법들로는 PWOL(Pre-emptive Weld Overlay), 레이저 피닝(Laser Peening), MSIP(Mechanical Stress Improvement Process), 워터 제트 피닝(Water Jet Peening), IHSI(Induction Heating Stress Improvement) 방법들이 있는데 공정 시간이 짧고 열 에너지 원이 필요 없으며 전체적인 소성 변형을 야기시키지 않는 레이저 피닝을 본 연구의 대상 방법으로 한다. 본 연구에서는 동적 유한요소 해석을 통해 용접 잔류응력을 이완시키는 레이저 피닝의 효과를 검증하고 용접 잔류응력에 미치는 레이저 피닝 변수의 영향을 고찰하고자 한다. 내부 보수용접이 수행된 경수로 원전 가압기 노즐 이종금속 용접부에 레이저 피닝을 적용한 경우에 대해 상용 유한요소 해석 프로그램인 ABAQUS를 이용하여 동적 유한요소해석을 수행한 결과, 고온 수화학 일차수와 접하는 Alloy 600 계열 합금 내면에서의 인장 잔류응력이 상당히 이완됨을 확인하였다. 또한, 최대충격 압력이 증가할수록, 충격압력 지속시간이 증가할수록, 레이저 스팟 직경이 증가할수록 내표면 인장 잔류응력 이완 정도는 감소하나 이완되는 영역의 깊이는 증가함을 알 수 있다. 또한, 레이저 피닝 방향이 잔류응력 이완에 미치는 영향은 미미함을 알 수 있다.