• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.527-532
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• 2000

The armor composite material targets such as aramid FRMLs with different type and ply number of face material and different type of back-up material, were studied to determine ballistic impact resistance and dynamic failure behavior during ballistic impact. Ballistic impact resistance is determined by $\textrm{V}_{50}$ ballistic limit, a statical velocity with 50% probability for complete penetration, test method. Also dynamic failure behaviors are respectfully observed that result from $\textrm{V}_{50}$ tests. $\textrm{V}_{50}$ tests with $0^{\circ}$ obliquity at room temperature were conducted with projectiles that were able to achieve near or complete penetration during high velocity impact tests. As a result, ballistic impact resistance of anodized Al 5052-H34 alloy(2 ply) is better than that of anodized Al 5052-H34 alloy(1 ply), but Titanium alloy showed the similar ballistic impact resistance. In the face material, ballistic impact resistance of titanium alloy is better than that of anodized Al 5052-H34 alloy. In the back-up material, ballistic impact resistance of T750 type aramid fiber is better than that of CT709 type aramid fiber.

• 대한기계학회논문집A
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• 제25권4호
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• pp.629-636
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• 2001

In order to investigate the possibility of impact punching in brittle materials, an experimental setup was developed. In the setup, a long bar as a punch was used to apply the impact load to the specimen plate and measure the applied impact force during the impact punching process. Impact punching tests with various shape of punches were performed in soda-lime glass and silicon wafer under a different level of contact pressure. The damage appearance after the impact punching was examined according to the applied contact pressure. The minimum contact pressure required for a complete punching in glass specimens without development of radial cracks around the punched hole was sought at each condition. The minimum contact pressure increased with increasing the thickness of specimens and decreasing the end radius of punches. The profile of impact forces was measured during the impact punching experiment, and it could explain well the behavior of the punching process in brittle material plates. The measured impact force increased with increasing the contact pressure applied to the plates.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1341-1344
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• 2003

Studies on impact damage of composite laminate shells were fewer compared with those on impact behaviors to analyze time-load, displacement-load and impact energy - energy absorption. Up to date the studies were not enough to demonstrate suitability of their results because they were dependent on theories and numerical analyses. In particular, it is a well-known fact that there was a correlation between initial peak load and damage resistance of composite material flat plates imposed with low-speed impact, but studies on composite material shells with curvature were also very few. Actually structures such as wings or moving bodies of airplanes, motor cases and pressure containers of rockets are circular. And as low-speed impact load is imposed for optimal design of take-off and landing, and containers of airplanes, it is very important to analyze evaluation of behaviors and damaged areas. Therefore, in this paper to evaluate the impact characteristics of the CFRP laminate shell according to size of curvature quantitatively, it was to identify energy absorption and impact damage instruments according to change of impact speed.

• Structural Monitoring and Maintenance
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• 제3권3호
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• pp.195-214
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• 2016

Monitoring of impact loads is a very important technique in the field of structural health monitoring (SHM). However, in most cases it is not possible to measure impact events directly, so they need to be reconstructed. Impact load reconstruction refers to the problem of estimating an input to a dynamic system when the system output and the impulse response function are usually known. Generally this leads to a so called ill-posed inverse problem. It is reasonable to use prior knowledge of the force in order to develop more suitable reconstruction strategies and to increase accuracy. An impact event is characterized by a short time duration and a spatial concentration. Moreover the force time history of an impact has a specific shape, which also can be taken into account. In this contribution these properties of the external force are employed to create a sample-force-dictionary and thus to transform the ill-posed problem into a sparse recovery task. The sparse solution is acquired by solving a minimization problem known as basis pursuit denoising (BPDN). The reconstruction approach shown here is capable to estimate simultaneously the magnitude of the impact and the impact location, with a minimum number of accelerometers. The possibility of reconstructing the impact based on a noisy output signal is first demonstrated with simulated measurements of a simple beam structure. Then an experimental investigation of a real beam is performed.

• 대한기계학회논문집
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• 제18권2호
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• pp.359-371
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• 1994

A drop weight type impact test system is designed and set up to experimentally investigate impact responses of composite laminates subjected to the low-velocity impact. Using the test system, the impact velocity and the rebound velocity of the impactor as well as the impact force history are measured. An error of the measured data due to a difference in measuring position of the sensor is corrected and, for the estimation of real contact force history, a method of correcting an error due to friction forces is developed. Experimental methods to fix the boundary edgy of laminate specimens in impact testing are investigated and the impact tests on the specimens fixed by those methods are performed. Impact force histories and dynamic strains measured from the tests are compared with numerical results from the finite element analysis using the contact law. Consequently, the nonlinear numerical results considering the large deflection effects are agreed with the experimental results better than the linear ones.

• 폴리머
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• 제26권2호
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• pp.270-278
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• 2002

저밀도 2-D 탄소/탄소 복합재료의 저속 충격에 의한 파괴 거동과 첨가제에 따른 충격 에너지 흡수 경향을 연구하였다. 저속 충격시험은 mini tower 낙추 충격 시험기를 이용하였으며, 흑연, 카본블랙, 분쇄탄소섬유를 첨가제로 선택하였다. 흑연의 첨가는 최대하중값을 증가시켰으며, 전체적인 관통이 일어나기까지 응력을 오랫동안 유지시키는 효과를 나타내었다. 특히 9 vol%의 함량에서 흑연이 첨가되지 않은 씨편보다 약 42%의 충격 흡수 개선을 보였다. 약 0.4 J의 낮은 충격에너지에 의한 충격 회수에 따른 실험에서 첨가제가 첨가되지 않은 시편의 경우, 충격에너지는 층간분리에 의해 소모되고, 흑연의 함량이 증가함에 따라 파괴 경향은 시편의 관통으로 변화함을 관찰할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.146-152
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• 1997

This paper deals with a study of striker type impact hammer drill for improving the drilling performance. The study was performed through a numerical simulation of the impact hammer mechanism, an experimental comparison of the numerical simulation results and an optimization of the impact mechanism. The numerical model of the impact hammer drill takes into account the striker motion and the effects of the pressure in the cylinder as well as the friction acting on the striker. The equation of motion is solved with the pressure equation in the cylinder and the friction force. At the moment of impact, an ideal impact model that uses restitutiion codfficient is used to calculate the sudden change of the striker motion. The impact force numerically simulated shows a good agreement with the experimental results and thus, the validity of the numerical model is proven. Based upon the proposed model, an optimization was performed to improve the impact force of the hammer drill. The objective function is to maximize the impact force and the design variables are striker mass, frequency of piston, bit guide mass, cylindrical diameter and dimensions of the mechanism components. Each design variable and some other conditions that are essential to maintain normal operation of the hammer drill are considered as constraints. The optimized result shows remarkable improvement in impact force and an experimental proof was investigated.

• 한국압력기기공학회 논문집
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• 제4권2호
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• pp.20-28
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• 2008

According to IAEA regulations, a transportation package of radioactive material should perform its intended function of containing the radioactive contents after the drop test, which is one of hypothetical accident conditions. Impact limiters attached to a transport cask absorb the most of impact energy. So, it is appreciated to determine properly the shape, size and material of impact limiters. A material data needed in this determination is a dynamic one. In this study, several materials considered as those of impact limiters were tested by a drop weight facility to acquire dynamic material characteristics data. Impact absorbing volume of the impact limiter was derived mathematically for each drop condition. A size optimization of impact limiter was conducted. The derived impact absorbing volumes were applied as constraints. These volumes should be less than critical volumes generated based on the dynamic material characteristics. The derived procedure to decide the shape of impact limiter can be useful at the preliminary design stage when the transportation package's outline is roughly determined and applied as input value.

• 한국조경학회지
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• 제27권5호
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• pp.66-79
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• 2000

Landscape impact assessment(LIA) is an aid to decision-making. For the decision maker, LIA provides a scientific examination of the predicted landscape implications of a proposed action and of the mitigation measures, before a decision is taken. Thus, the efficacy of LIA depends on the scientific credibility of the prediction and mitigation measures described in the landscape impact statement. The purpose of this paper was to examine the efficacy of LIA through the content analysis of prediction and mitigation measures in the selected 39 landscape impact statements and 34 environmental impact statements. The content of the selected statements was analyzed in terms of the quantification, precision, significance, and likelihood. The results showed that both prediction and mitigation measures were very low in the scientific credibility. Specifically, the prediction was ambiguously described without scientific probability, and the effect of mitigation measures was not specifically presented in the reports. Thus, landscape impact statement can not give credible information in the decision making process, which weakens the efficacy as an aid to decision-making. Based on the results, several suggestions were presented to enhance the efficacy of LIA.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1998년도 제13차 학술회의논문집
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• pp.295-300
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• 1998

In this paper, a real time diagnostic algorithm fur estimating the impact location by loose parts is proposed. It is composed of two modules such as the alarm discrimination module (ADM) and the impact-location estimation module(IEM). ADM decides whether the detected signal that triggers the alarm is the impact signal by loose parts or the noise signal. When the decision from ADM is concluded as the impact signal, the beginning time of burst-type signal, which the impact signal has usually such a form in time domain, provides the necessary data fur IEM. IEM by use of the arrival time method estimates the impact location of loose parts. The overall results of the estimated impact location are displayed on a computer monitor by the graphical mode and numerical data composed of the impact point, and thereby a plant operator can recognize easily the status of the impact event. This algorithm can perform the diagnosis process automatically and hence the operator's burden and the possible operator's error due to lack of expert knowledge of impact signals can be reduced remarkably. In order to validate the application of this method, the test experiment with a mock-up (flat board and reactor) system is performed. The experimental results show the efficiency of this algorithm even under high level noise and potential application to Loose Part Monitoring System (LPMS) for improving diagnosis capability in nuclear power plants.