• Composites Research
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• v.29 no.1
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• pp.1-6
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• 2016

Low-speed impact was localized on a stiffened composite structure, using 4 FBG sensors with 100 kHz-sampling rate interrogator and devised localization algorithm. The composite specimen consists of a main spar and several stringers, and the overall size of the specimen's surface is about $0.8{\times}1.2m$. Pre-stored reference data for 247 grid locations and 36 stiffener locations are gathered and used as comparison target for a random impact signal. The proposed algorithm uses the normalized cross-correlation method to compare the similarities of the two signals; the correlation results for each sensor's signal are multiplied by others, enabling mutual compensation. 20 verification points were successfully localized with a maximum error of 43.4 mm and an average error of 17.0 mm. For the same experimental setup, the performance of the proposed method is evaluated by reducing the number of sensors. It is revealed that the mutual compensation between the sensors is most effective in the case of a two sensor combination. For the sensor combination of FBG #1 and #2, the maximum localization error was 42.5 mm, with average error of 17.4 mm.

• 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.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.1
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• pp.8-13
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• 2016

The purpose of the pyro-shock compliant joint is to isolated vibration using the compliant material in order to prevent the shock generated by pyro propulsion at the electronics equipment. The performance of the pyro-shock compliant joint can be determined by measuring bending natural frequency and transmissibility. In this study, we established the design requirements based on bending natural frequency and transmissibility results of the reference model. We developed a compliant material with sufficient shock compliant properties and a pyro-shock compliant joint for the new rocket. This results can be used to develop a pyro-shock compliant joint for any rocket using the compliant material and performance measurement.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.33-36
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• 2008

It is generally known that a shell in the form of layered structures stacked up thin elements by organic adhesives has high resistance capacity against static and impact loading. The complex materials such as these diversified layered structures are more reliable and efficient to the impact loading than the single material. In this study, the segmented composites in the shape of a beam were made, using mortar and concrete block and tested under static and impact loading in order to develop the complex materials in the form of layered structures as the segmented composites to resist impact loading. And it compared to the normal concrete beams having the same compressive strength to evaluate the differences in their performance and failure modes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.321-328
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• 2009

Shock absorption performances of various rubbers were investigated by using drop impact test. Several types of rubber such as NR, NBR, EPDM, SR and PUR with three respective levels of shore hardness were used for the test. As in the cases, the absorbed impact energies in rubbers were measured under seven different loads against impact energy between 5-80J. The impact absorption efficiencies of the rubbers then were evaluated by means of both single impact energy condition and summation of all impact energy applied condition. As shown in the results, PUR and EPDM have better shock absorption performances than other rubbers. Further analysis was extended to determine a shear modulus of SR through the finite element implementation with Blatz-Ko model. As can be seen, relatively higher level of absorption energy results in a decreasing shear modulus.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05b
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• pp.15-18
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• 2004

피뢰기에 뇌 또는 이상전압과 같은 정격이상의 고장전류가 유입되어 발생하게 되는 순간적인 열 충격과 내부압력 상승은 폭탄이 내부에서 터지는 것과 같은 엄청난 양의 충격에너지이다. 본 연구에 있어서 폴리머 피뢰기의 제조에 사용된 모듈용 브레이드 복합재료는 압력해소 및 폭발 비산하지 않도록 하는 기능을 수행하도록 설계되어있다. 기존의 폴리머 피뢰기에 적용된 복합재료보다 충격에너지를 흡수하는 구조물에 유리한 브레이드 복합재료를 피뢰기 모듈의 제조에 도입한 것은 매우 의미 있는 일이라 판단된다. 따라서 본 연구에서는 열경화성 브레이드 복합재료를 제조하기 위하여 프리폼을 먼저 제작한 다음 금형에 삽입한 후 진공상태에서 수지를 주입하여 경화시키는 RTM공법을 이용하였다. 본 연구의 목적은 브레이드 패턴 및 방압개소 설계 등의 기초적인 자료조사 및 실험을 통하여 폴리머 피뢰기의 폭발 비산을 방지할 수 있는 압력해소 성능을 위한 기초 자료를 확보하고자 하는 것이다. 브레이드 복합재료의 기본적인 경화거동을 등온 및 동적 DSC를 이용하여 고찰하였고, 기본적인 전기적 특성을 평가하였으며, 방압개소를 가진 폴리머 피뢰기 모듈의 고장전류시험시 예상되는 열 충격에 대한 성능을 검증하기 위하여 열팽창계수를 측정하였다.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.369-379
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• 2012

The collapse of concrete structures by extreme loads such as impact, explosion, and blast from terrorist attacks causes severe property damage and human casualties. Concrete has excellent impact resistance to such extreme loads in comparison with other construction materials. Nevertheless, existing concrete structures designed without consideration of the impact or blast load with high strain rate are endangered by those unexpected extreme loads. In this study, to improve the impact resistance, the static and impact behaviors of concrete beams caste with steel fiber reinforced concrete (SFRC) with 0~1.5% (by volume) of 30 mm long hooked steel fibers were assessed. Test results indicated that the static and impact resistances, flexural strength, ductility, etc., were significantly increased when higher steel fiber volume fraction was applied. In the case of the layered concrete (LC) beams including greater steel fiber volume fraction in the tensile zone, the higher static and impact resistances were achieved than those of the normal steel fiber reinforced concrete beam with an equivalent steel fiber volume fraction. The impact test results were also compared with the analysis results obtained from the single degree of freedom (SDOF) system anaysis considering non-linear material behaviors of steel fiber reinforced concrete. The analysis results from SDOF system showed good agreement with the experimental maximum deflections.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.449-455
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• 2001

도로교통소음의 저감을 위해 설치되는 방음벽의 성능평가를 위해서는 흡음률 및 투과손실과 같은 음향성능에 대한 평가뿐만 아니라, 풍압 및 충격하중과 같은 구조성능과 방음판 제작에 사용되는 재질에 관한 성능평가도 수반되어야 한다. 따라서, 본 논문에서는 이러한 방음벽의 성능평가를 위한 음향 구조 및 재질에 관한 시험 및 평가방법을 제시하였다.

• Composites Research
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• v.29 no.2
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• pp.73-78
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• 2016

In this paper, The concept of a wheel with carbon fiber composite is to replace the conventional material used for a wheel hub, such as plastic, with a disk-type hub made of carbon fabric and epoxy resin. The impact load from the ground under real conditions was considered; a low-velocity impact test was conducted to evaluate the impact performance of the carbon wheel and compare it with that of a conventional plastic wheel. This study applied a 70 J impact load as a test condition. The impact energy was controlled in the test by adjustment of height and weight of impactor. The use of a carbon disk wheel hub was confirmed to reduce weight and generate an excellent repulsive force at low energy under conditions similar to real driving conditions. The results showed that the maximum load increased proportionally depending on the impact load, but the growth of the maximum load was reduced at a 20 J impact load and tended to decrease at a 45 J impact load. The carbon wheel showed excellent properties ; the level of rebounding was 35.3% and 19.1% of the total impact energy at impact loads of 5 J and 10 J, respectively. On the other hand, the carbon disk wheel rebounded less than 5% of the total energy due to crack generation of the thin carbon hub for impact loads of more than 20 J.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.6
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• pp.83-88
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• 2005

In this paper, detection based - adaptive windowed nonlinear filters(DB-AWNF) are proposed for removing one-side impulse noise in infrared image. They are composed of impulse detector and window-size-variable median filters. Impulse detector checks whether current pixel is impulse or not using range function and nonlinear location estimator. If impulse is detected, current pixel is filtered according to four kinds of local masks by use of median filter. If not. current pixel is delivered to output like identity filter. In qualitative view, the proposed could have removed heavy corrupted noise up to $20\%$ and reserved the details of image. In quantitative view, PSNR was measured. The proposed could have 13 - 31[dB] more improved performance than those of median($3{\times}3$) filter and 18 - 25[dB] more improved performance than those of median($5{\times}5$) filter.