• Computers and Concrete
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• 제3권2_3호
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• pp.79-90
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• 2006

This paper describes the results of an investigation into high mass-low velocity impact behaviour of reinforced concrete beams. Tests have been conducted on fifteen 2.7 m or 1.5 m span beams under drop-weight loads. A high-speed video camera has been used at rates of up to 4,500 frames per second in order to record the crack formation, propagation, particle spallation and scabbing. In some tests the strain in the reinforcement has been recorded using "Durham" strain gauged bars, a technique developed by Scott and Marchand (2000) in which the strain gauges are embedded in the bars, so that the strains in the reinforcement can be recorded without affecting the bond between the concrete and the reinforcement. The impact force acting on the beams has been measured using a load cell placed within the impactor. A high-speed data logging system has been used to record the impact load, strains, accelerations, etc., so that time histories can be obtained. This research has led to the development of computational techniques based on combined continuum/discontinuum methods (finite/discrete element methods) to permit the simulation of impact loaded reinforced concrete beams. The implementation has been within the software package ELFEN (2004). Beams, similar to those tested, have been analysed using ELFEN a good agreement has been obtained for both the load-time histories and the crack patterns.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
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• pp.75-76
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• 2015

This study has examined the impact resistance and blast resistance characteristics of HPFRCC as a research on impact resistance and blast resistance characteristics using high volume mortar and high velocity projectile for evaluating the protection performance of actual buildings as small quantity experiment of laboratory conditions is performed although there was an instance of performing research on mortar that has reinforced fiber followed by the rise of problems on the damage of human life and buildings created due to explosion and shock. As a result, the destruction loss area and depth have decreased in case of the surface compared to the rear side. As tensile strength and tenacity have increased with the increased fiber replacing ratio, a tendency of destruction loss area and depth getting decreased was shown as the impact resistance has increased.

• 한국운동역학회지
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• 제16권3호
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• pp.43-51
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• 2006

The purpose of this study was to analyze kinematic variables during turing back kick motion of Taekwondo. The subjects of this study were the 4 skilled and 4 unskilled of male university player in respectively. The experiment of this study was used two 16mm high speed cameras and its speed 125 frames/s. Analysis of this data was three dimensional cinematography using KWON3D program package. The results were as following; 1. In the elapsed time, there was no significance difference statically between a skilled and unskilled group. But skilled group was more fast during the motion of I phase. And unskilled group was more fast during the motion of II phase so called force production section, which had an influence on Diechagi's velocity. 2. In the center of gravity of human body, the changing of it was $1.10{\pm}0.04m$, $1.12{\pm}0.03m$ of LFM(left foot movement) and $1.36{\pm}0.08m$, $1.39{\pm}0.09m$ of RKF(right knee flection), and $1.44{\pm}0.08m$, $1.42{\pm}0.09m$ of RFI(right foot impact). There was no significance difference statically between the two groups. 3. The velocity of heel on impact was 1.13m/s in the skilled group and 1.23m/s in the unskilled group, when each angle of knee was $110.4{\pm}10.9deg/s$, $114.8{\pm}28.4deg/s$. The maximum velocity of each performance was reached before the RKF, and the velocity and angle at impact along by two groups did not show any significant difference statically. 4. In the angular velocity of just RKF of lower leg, there was significance difference statically between the two groups(p<.05).

• 한국항공우주학회지
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• 제41권2호
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• pp.120-126
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• 2013

현재 자연적 또는 인공적으로 늘어난 지구 주위의 수많은 미세 입자들은 인공위성에 위협이 되고 있으며 인공위성과 우주 먼지간의 충돌 속도는 수 km/s에 이른다. 본 연구에서는 이러한 우주 먼지를 모사하기 위하여 작은 금속판을 레이저를 이용하여 가속하였다. 기존 연구에서는 다중코팅을 이용하여 속도 효율을 향상시켰으나 코팅하는데 시간과 비용이 많이 드는 단점이 있었다. 본 연구에서는 그러한 다중코팅 대신 단순한 검은색 페인트를 이용하여 코팅을 하지 않았을 때보다 1.5~2배 정도의 속도향상을 보였으며 Nd:YAG 레이저를 이용하여 1.4J이하에서 최대 1.42km/s의 속도를 얻었다. 이 속도는 정지궤도에서의 인공위성과 우주먼지 충돌을 모사하는데 적합하다.

• 대한기계학회논문집A
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• 제24권7호
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• pp.1863-1870
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• 2000

When an impact stress is applied on the external boundary of double cantilever beam of orthotropic material which crack length is greater than specimen hight and anistropic ratio is very high, dyna mic energy release rate is derived, and the relationship between dynamic energy release rate and crack propagating velocity is studied. Dynamic energy release rate to static energy release rate is decreased with increasment of crack propagating velocity. The relationships between dynamic energy release rate and vertical strain have a similar pattern with those between static energy release rate and vertical strain. When normalized time(Cstla) is greater than or equal to 2, dynamic energy release rate approaches to a constant value.

• 대한기계학회논문집B
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• 제27권8호
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• pp.1165-1173
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• 2003

The effects of (1) phonon dispersion on thermal conductivity model and (2) differentiation of group velocity and phase velocity are examined for germanium. The results show drastic change of thermal conductivity regardless of the same relaxation time model. Also the contribution of transverse acoustic (TA) phonon and longitudinal acoustic (LA) phonon on the thermal conductivity at high temperatures is reassessed by considering more rigorous dispersion model. Holland model, which is commonly used for modeling thermal conductivity, underestimates the scattering rate for TA phonon at high frequency. This leads the conclusion that TA is dominant heat transfer mode at high temperatures. But according to the rigorous consideration of phonon dispersion, the reduction of thermal conductivity is much larger than the estimation of Holland model, thus the TA at high frequency is expected to be no more dominant heat transfer mode. Another heat transfer mechanism may exist at high temperatures. Two possible explanations we the roles of (1) Umklapp scattering of LA phonon at high frequency and (2) optical phonon.

• 한국염색가공학회지
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• 제28권4호
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• pp.246-252
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• 2016

In comparison to metal alloys, braided composite features a high impact resistance and crash energy absorption potential, and also it still remained competitive stiffness and strength properties. Braiding angle is one of the most important parameters which affect the mechanical behaviors of braided composite. This paper presents transverse low velocity impact failure behavior analysis on the carbon 3D triaxial braided composite tube with the braiding angle of $20^{\circ}$, $50^{\circ}$ and $80^{\circ}$. The flexural behaviour of 3D triaxial braided composite tube under bending loads was studied by conducting quasistatic three point bending test. Also, the low velocity impact responses of the braided composite tubes were also tested to obtain load-displacement curves and energy absorption. Consequently, the increase of the braided angle, the peak load also increases owing to the bigger bending stiffness.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.561-566
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• 2008

Recently, because of development of the high speed train technology, the vibration loads by train is significantly increased ever than before. This buried gas pipelines are exposed to both repeated impact loads, and, moreover, they have been influencing by vibration loads than pipeline which is not located under vehicle loads. The vibration characteristic of pipeline is examined by dynamic analysis, and variable is only train speed. Since an effect of magnitude of vibration loads is more critical than cover depth, as increasing the train speed, the vibration speed of buried pipelines is also increased. The slope of vibration velocity is changed by attenuation of wave, at train speed, 300 km/h. From the analysis results, the vibration velocity of pipelines is satisfied with the vibration velocity criteria which are established by Korea Gas Corporation. The results present operation condition of pipelines under rail loads has fully sound integrity based on KOGAS specification.

• 한국방재학회 논문집
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• 제9권3호
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• pp.49-57
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• 2009

충돌사고시 스마트하이웨이의 정시성과 안전성의 손상정도를 최소화 하도록 스마트하이웨이의 종방향 방호울타리 충돌조건으로 기존의 충돌조건보다 상당히 상향된 충돌조건이 결정되었다. 충돌조건은 충돌차량, 충돌속도, 충돌각도로 구성된다. 가능한 많은 승용차의 탑승자 안전을 고려할 수 있도록 충돌시 피해가 크게 나타나는 작은 차량을 충돌차량으로 선정 하였다. 가능한 많은 사고 충돌속도를 포함하도록 기존의 충돌속도보다 20% 큰 충돌속도가 결정되었다. 충돌각도는 예상되는 사고 충돌각도를 거의 모두 포함하도록 결정되었다. 기존의 국내 최고성능등급의 종방향 방호울타리에 대하여 다양한 충돌조건을 적용한 시뮬레시션을 수행하고 그 결과를 분석하여 제시된 스마트하이웨이 충돌조건이 탑승자 안전에 미치는 영향을 파악하였다. 기존의 국내 최고성능등급의 종방향 방호울타리는 제시된 스마트하이웨이 충돌조건을 만족하지 못하였다. 충돌사고시 스마트하이웨이의 정시성과 안전성의 손상정도를 최소화 하기 위해서 새로운 고성능의 종방향 방호울타리가 필요하다고 판단된다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 봄 학술발표회 논문집
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• pp.111-118
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• 2004

For the precise analysis of high velocity impact problem though FEM with element erosive method, the adequate mesh size and critical equivalent plastic strain(EQPS) is chosen prior to the simulation. In this research, it is strongly required from a standpoint that critical EQPS is used to decide whether perforation occurs or not. The optimization of dual armor plate consisting of 4340 steel and 2024 aluminium against a die steel sphere with high-velocity has been suggested using Lagrangian explicit time-integration code, NET2D. The response surface method based on the design of experiment is utilized for the size optimization. The optimized thickness of each layer, in which perforation does not occur, the strength of multi-layer is maximized and total weight is minimized, is obtained at a constant velocity of a pellet with a designated total thickness.