• Title/Summary/Keyword: 고속충격

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Evaluation on Rear Fracture Reduction and Crack Properties of Cement Composites with High-Velocity Projectile Impact by Fiber Types (섬유 종류에 따른 시멘트복합체의 고속 비상체 충격에 대한 배면파괴저감 및 균열특성 평가)

  • Han, Sang-Hyu;Kim, Gyu-Yong;Kim, Hong-Seop;Kim, Jung-Hyun;Nam, Jeong-Soo
    • Journal of the Korea Concrete Institute
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    • v.27 no.2
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    • pp.157-167
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    • 2015
  • Cement composites subjected to high-velocity projectile shows local failure and it can be suppressed by improvement of flexural toughness with reinforcement of fiber. Therefore, researches on impact resistance performance of cement composites are in progress and a number of types of fiber reinforcement are being developed. Since bonding properties of fiber with matrix, specific surface area and numbers of fiber are different by fiber reinforcement type, mechanical properties of fiber reinforced cement composites and improvement of impact resistance performance need to be considered. In this study, improvement of flexural toughness and failure reduction effect by impact of high-velocity projectile have been evaluated according to fiber type by mixing steel fiber, polyamide, nylon and polyethylene which are have different shape and mechanical properties. As results, flexural toughness was improved by redistribution of stress and crack prevention with bridge effect of reinforced fibers, and scabbing by high-velocity impact was suppressed. Since it is possible to decrease scabbing limit thickness from impact energy, thickness can be thinner when it is applied to protection. Scabbing of steel fiber reinforced cement composites was occurred and it was observed that desquamation of partial fragment was suppressed by adhesion between fiber and matrix. Scabbing by high-velocity impact of synthetic fiber reinforced cement composites was decreased by microcrack, impact wave neutralization and energy dispersion with a large number of fibers.

Influence Factor Analysis of Projectile on the Fracture Behavior of Aluminum Alloys Under High Velocity Impact with Latin Square Method (라틴방격법을 이용한 고속 충격 알루미늄합금의 파괴거동에 미치는 충격자 영향 분석)

  • Kim, Jong-Tak;Cho, Chang-Hee;Kim, Jin-Young;Kim, Tae-Won
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.9
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    • pp.1021-1026
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    • 2011
  • Structural impact problems are becoming increasingly important for a modern defense industry, high-speed transportation, and other applications because of the weight reduction with high strength. In this study, a numerical investigation on the impact fracture behavior of aluminum plates was performed under various projectile conditions such as nose shapes, velocities, and incidence angles. In order to reduce the iterative numerical analysis, the Latin Square Method was employed. The influence factor was then determined by an FE analysis according to the conditions. The results were evaluated by means of a statistical significance interpretation using variance assessment. It was shown that the velocity and incidence angle can be the most important influence factors representing the impact absorption energy and plastic deformation, respectively.

Dynamic Failure Behavior of Ceramic/Fiber-Reinforced Composites under High Speed Impact Loading (고속충격에 의한 세라믹/섬유강화 복합재료의 동적파손 거동)

  • Kim, Hui-Jae;Yuk, Jong-Il;Lee, Seung-Gu
    • Korean Journal of Materials Research
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    • v.7 no.9
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    • pp.795-804
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    • 1997
  • 전면재를 알루미나, 후면재를 Kevlar또는 S-2 유리 섬유강화 복합재료로 접합한 이종재료 장갑에 대하여 알루미나의 두께 변화와 복합재료의 적층구조에 따른 고속충격 특성 변화에 대하여 연구하였다. 또한 시험재료의 동적 관통현상을 분석하기 위하여 고속촬영기법이 이용되었다. 시험결과, 전면재인 알루미나는 충격탄자 직경의 80% 상당하는 두께(본 실험에서는 6nm)인 경우 양호한 방탄성능을 보였다. 후면재인 복합재료는 섬유를 alternating 주조로 적층한 경우가 laminar구조로 적층한 것에 비하여 더 우수한 방탄성능을 나타내었다.

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Detection of High-Velocity Impact Damage in Composite Laminates Using PVDF Sensor Signals (고분자 압전 필름 센서를 이용한 복합재 적층판의 고속 충격 손상 탐지)

  • Kim Jin-Won;Kim In-Gul
    • Composites Research
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    • v.18 no.6
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    • pp.26-33
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    • 2005
  • The mechanical properties of composite materials may severely degrade in the presence of damage. Especially, the high-velocity impact such as bird strike, a hailstorm, and a small piece of tire or stone during high taxing, can cause considerable damage to the structures and sub-system in spite of a very small mass. However, it is not easy to detect the damage in composite plates using a single technique or any conventional methods. In this paper, the PVDF(polyvinylidene fluoride) film sensors were used for monitoring high-velocity impact damage initiation and propagation in composite laminates. The WT(wavelet transform) and STFT(short time Fourier transform) are used to decompose the sensor signals. A ultrasonic C-scan and a digital microscope are also used to examine the extent of the damage in each case. This research shows how various sensing techniques, PVDF sensor in particular, can be used to characterize high-velocity impact damage in advanced composite.

Study on Behavior Analysis of Crash Cushion Using Analysis Data of High-Speed Camera (고속카메라 영상분석 데이타를 이용한 충격흡수시설의 충돌거동 분석에 관한 연구)

  • Jang, Dae-Young;Ko, Man-Gi;Lee, Yoon-Ki;Joo, Jae-Woong
    • International Journal of Highway Engineering
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    • v.11 no.2
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    • pp.75-83
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    • 2009
  • Collision behavior of clash cushion occurs for a second of less than 0.4sec usually so that it is too hard to calculate numerically. Therefore, for development of trash cushion, it rely on full-scale vehicle crash test without any design procedure. Occupant safety indices if calculated from acquired data by data measurement system and collision behavior of vehicle and crash cushion is filming using high-speed camera in the crash test. But practical ufo scope of high-speed camera is limited and it is not using to calculated the occupant safety indices or analyzed the energy dissipated mechanism of crash cushion. This work is to estimate to be suitable or not for compare the data from measurement system with the data from high-speed camera. And also it is to grope for practical use scheme to calculation of occupant safety indices or analysis of collision behavior.

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High-Velocity Impact Experiment on Impact Resistance of Steel Fiber-Reinforced Concrete Panels with Wire Mesh (와이어매쉬와 강섬유로 보강된 콘크리트 패널의 내충격성 규명을 위한 고속충격실험)

  • Kim, Sang-Hee;Hong, Sung-Gul;Yun, Hyun-Do;Kim, Gyu-Yong;Kang, Thomas H.K.
    • Journal of the Korea Concrete Institute
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    • v.27 no.2
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    • pp.103-113
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    • 2015
  • This paper studies impact performance of wire-mesh and steel fiber-reinforced concrete based on high-velocity impact experiments using hard spherical balls. In this experimental study, panel specimens were tested with various parameters such as steel fiber volume fraction, presence/absence of wire mesh, panel thickness, impact velocity, and aggregate size for the comparison of impact resistance performance for each specimen. While improvement of the impact resistance for reducing the penetration depth is barely affected with steel fiber volume fraction, the impact resistance to scabbing and perforation is improved substantially. This was due to the fact that the steel fiber had bridging effects in concrete matrix. The wire mesh helped minimizing the crater diameter of front and back face and enhanced the impact resistance to scabbing and perforation; however, the wire mesh did not affect the penetration depth. The wire mesh also reduced the bending deformation of the specimen with wire mesh, though some specimens had splitting bond failure on the rear face. Additionally, use of 20 mm aggregates is superior to 8 mm aggregates in terms of penetration depth, but for reducing the crater diameter on front and back faces, the use of 8 mm aggregates would be more efficient.

Simulation and Design of High-Speed Hydraulic Velocity Generator in Shock Test Machine (충격시험장치 고속유압 속도발생기 해석 및 설계)

  • Kim, Tae Hyeong;Shul, Chang Won;Kim, Yoon Jae;Yang, Myung Seog;Lee, Gyu Sub
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.6
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    • pp.663-668
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    • 2014
  • Mechanical and electrical devices in various forms are used in many different fields. These can be exposed to external environmental factors such as shock. Therefore, a shock test machine is commonly used to test these devices and evaluate their shock resistance. In this test, the break-down or permanent deformation and malfunction of inner parts due to a high stress or acceleration can be evaluated. As part of a shock test machine, a velocity generator is needed to create shocks between objects. In this study, a hydraulic velocity generator was conceptually designed and an AMESim model was developed to simulate the velocity under different conditions. Simulation results using this model were compared with the test results from a reduced-size velocity generator, and we designed a velocity generator that fits the target payload and velocity using the simulation results.

축소형 로켓 엔진의 소음 특성 연구

  • 조남경;문일윤;정용갑;오승협
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2000.04a
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    • pp.31-31
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    • 2000
  • 로켓 엔진은 고속의 고온 고압 제트가 분출함으로 인해 현존하는 소음 소스 수준 중 가장 큰 소음을 발생시킨다. 로켓 엔진에서 생기는 소음은 충격소음과 유동소음으로 구분할 수 있다. 충격소음은 연소제트의 불완전 팽창으로 인한 shock cell의 영향으로 shock wave가 발생하게 되어 고속의 제트가 대기와 충동함으로 인해 형성되는 충격파로 인해 발생되는 소음이며 유동소음은 mixing의 초기부분에서 초음속의 High velocity gas가 주변대기와 부딪히면서 생기는 난류와 전단력 때문에 발생하는 압력의 요동이 그 원인이 되어 고주파 소음의 특성을 띤 작은 eddy들에 의해 발생하는 소음이다.

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Finite Element Simulation of High-Speed Impact in Plane Structure (고속충격하중을 받는 평면구조의 유한요소해석)

  • 황갑운
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.12 no.2
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    • pp.119-128
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    • 1999
  • 본 연구는 등방탄성체에 고속충격하중이 작용하는 경우에 대한 유한요소해석에 관한 것으로 대상구조는 여러 가지 모양의 2차원 평면구조를 택하였다. Galerkin 방법을 이용하여 유한요소 정식화하였으며 직접시간적분법에 의해 수치해를 구하였다. 본 해석에서는 균열이 없는 평판으로 수치해와 이론해를 비교하여 수치해의 신뢰성을 확인하였으며, 0°, 30°, 45°경사 균열이 없는 평판에 적용한 3가지 예를 분석하였다. 수치해석 결과는 이론해의 결과와 상호 잘 일치하였다.

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Analytical Evaluation of High Velocity Impact Resistance of Two-way RC Slab Reinforced with Steel Fiber and FRP Sheet (강섬유 및 FRP Sheet로 보강한 2방향 RC 슬래브의 고속 충격저항성능에 대한 해석적 평가)

  • Lee, Jin Young;Shin, Hyen Oh;Min, Kyeng Hwan;Yoon, Young Soo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.17 no.3
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    • pp.1-9
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    • 2013
  • This paper presents high-velocity impact analysis of two-way RC slabs, including steel fibers and strengthening with fiber reinforced polymer (FRP) sheets for evaluating impact resistance. The analysis uses the LS-DYNA program, which is advanced in impact analysis. The present analysis was performed similarly to the high-velocity impact tests conducted by VTT, the technical research center of Finland, to verify the analysis results. High-velocity impact loads were applied to $2100{\times}2100{\times}250$ mm size two-way RC slab specimens, using a non-deformable steel projectile of 47.5kg mass and 134.9m/s velocity. In this research, extra impact analysis of material specimens was carried out to verify the material models used to the analysis. The elastic-plastic hydrodynamic model, concrete damage model and orthotropic elastic model were used to simulate the non-linear softening behavior of steel fiber reinforced concrete (SFRC), and material properties of normal concrete and FRP sheets, respectively. It is concluded that the suggested analysis technique has good reliability, and can be effectively applied in evaluating the effectiveness of reinforcing/retrofitting materials and techniques. Also, the Steel fiber and FRP sheet strengthening systems provided outstanding performance under high-velocity impact loads.