• Composites Research
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• v.24 no.6
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• pp.49-55
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• 2011

The use of advanced composite materials in main structures of military and civil aircraft has been increased rapidly because of their considerable metals in high specific strength and stiffness. However, the mechanical properties of composite materials may severely degrade in the presence of damage. Especially, the high-velocity impact such as 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 sensor or any conventional methods. In this paper, the PVDF sensors and AE sensors were used for monitoring high-velocity impact damage initiation and propagation in composite laminates. The WT(wavelet transform) is used to decompose the sensor signals. In the PVDF sensor and AE sensor signal analysis, amounts of high-frequency signals are increased when the impact energy is increased. PVDF sensor and AE sensor signal appeared similar results. This study shows how various sensing techniques can be used to characterize high-velocity impact damage of advanced composite laminates.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.2
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• pp.81-88
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• 1997

Impact behavior of carbon fiber reinforced plastics (CFRP) laminates were evaluated with tension test and compact tension test. A steel ball launched by an air gun collides against CFRP laminates to generate impact damage of relatively low energy. The static tensile and fracture toughness tests were performed to evaluate the residual strength and the AE behavior of impact-damaged laminates. As a results, it was found that the static strength, the fracture toughness and the AE-event count were decreased with increasing of impact velocity and delamination area, and to have a different strength ratio and fracture toughness ratio for each stacking method. And also, it was confirmed that strength and fracture toughness of impact-damaged CFRP laminates could be evaluated and analyzed quantitatively by AE techniques.

• Journal of IKEEE
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• v.3 no.1 s.4
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• pp.101-108
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• 1999

In this paper, a real time diagnostic algorithm for 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). First, ADM decides whether the detected signal that triggers the alarm is the impact signal by loose parts or the noise signal. Second, IEM by use of the arrival time method estimates the impact location of loose parts. 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.

• Journal of the Korean Geotechnical Society
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• v.16 no.3
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• pp.131-144
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• 2000

본 연구는 비검측공 시험법으로서 널리 사용되고 있는 충격반향기법(impact-echo test)의 적용서을 수치해석 및 실내 실험을 통하여 분석해 보았다. 즉, 결함이 없는 말뚝과 결함이 있는 말뚝에 대하여 1차원 및 2차원 축대칭 유한요소해석을 실시하였으며, 또한 모노캐스트라고 하는 일종의 플라스틱 원형 봉의 말뚝에 축대창 공극, 비축대칭 공극, 병목부 및 단면 확대부와 같은 결함을 각각 크기와 깊이를 변화시켜 제작한 후 공기 중과 지반 내부에서 충격반향기법 실험을 수행하였다. 실험결과 충격반향기법의 말뚝 결함 탐지능력은 수치해석에서 얻은 결과와 함께 결함의 크기와 위치에 영향을 받는 것으로 나타났으며 결함의 크기가 커질수록 탐지의 정확도가 향상되는 것을 알 수 있었다. 결함의 상대면적이 말뚝 단면적의 50% 이상이면 충격반향기법에 의하여 결함의 위치를 파악할 수 있는 것으로 나타났으며, 공기 중 보다 지반에 근입 된 말뚝의 경우가 더욱 명확한 신호를 제공해주는 것으로 나타났다. 그리고 시간영역의 신호가 주파수 영역의 신호 보다 말뚝의 결함 크기에 더 민감히 반응하므로 주파수 영역에서 탐지할 수 없는 작은 크기의 결함을 시간 영역에서는 탐지할 수 있는 것으로 나타났다.

• Composites Research
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• v.27 no.4
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• pp.141-145
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• 2014

This paper presents a structural health monitoring method using piezoelectric paint sensor designed for an impact sensor. The piezoelectric paint sensor can be flexibly deposited onto most structural surfaces in a thin form of the paint, and measure impact signals without any external device such as a power amplifier. In this study, a composite plate having four zones coated with piezoelectric paint was used for impact monitoring test. The sensitivity of the piezoelectric paint sensor was obtained by measuring the output voltages against the impact force. In addition to the sensitivity measurement, the impact position has been also estimated by comparing the output signals of the paint sensors when the impact occurs on the specimen.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.915-916
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• 2006

본 논문은 원자력 발전소의 금속파편감시계통(LPMS)에서 충격신호의 탐지를 위해 사용되는 하드웨어 구현에 관한 것이다. 본 논문에서 구현한 것은 LPMS의 하드웨어 중에서 입력된 신호를 디지털로 변환하여 충격신호의 트리거 판단기능을 하는 DAM(Data acquisition module)보드이다. 본 논문에서 구현한 DAM은 디지털 필터와 트리거 판단을 위한 알고리즘이 DSP에서 실시간으로 처리되어 LPMS의 기능을 업그레이드 하였다.

• 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.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.3.2-6
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• 1998

본 논문에서는 실측된 실내 충격 응답을 모델링하여 실내 잔향 필터 설계를 시도하였다. 급강하법(steepest descent method)을 이용하여 측정된 실내 충격 응답을 4개의 콤 필터(comb filter)와 2개의 올패스 필터(allpass filter)로 이루어진 잔향 필터로 모델링하여, 잔향 필터의 계수를 결정하였다.

• Composites Research
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• v.13 no.1
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• pp.89-97
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• 2000

Fatigue damage detection and vibration sensing for a laminated composites and impact location detection for a steel beam have been carried out using optical fiber sensor. Intensity based optical fiber sensor is constructed by placing two cleaved fiber end in a hollow glass tube, and multiple reflection within the cavity is considered. Fatigue signals are measured by embedded optical fiber, surface mounted optical fiber sensor and strain gage simultaneously. For vibration sensing, optical fiber sensor is mounted on the carbon fiber composite beam and its response to free vibration and forced vibration is investigated. In impact location detection, two optical fiber sensors are used and the information obtained from two sensors is arrival time delay of vibration caused by impact. Impact location can be calculated from this time delay. The obtained results show that the intensity based optical fiber sensor provide reliable data during long-term fatigue loading, unlike strain gage which deteriorate during the early part of the fatigue test. Optical fiber sensor signals coincide with gap sensor in vibration sensing. The precise locations of impact can be detected within 4.1% error limit.

• Journal of Aerospace System Engineering
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• v.13 no.2
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• pp.19-25
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• 2019

To detect the impact location of a structure, the authors' group conducted a study on piezoelectric paint sensor. The piezoelectric paint sensors are used for impact detection due to their inherent characteristics: sensitivity to high-frequency signal and impact. Additionally, the paint sensor can be applied on curved and complex structures where ceramic sensor would not be applicable. Moreover it is a self-powered sensor therefore no need for an external power source. For impact localization, mosaic pattern electrodes were coated on the specimen and the impact signal obtained from any part of the electrode where the impact occurred. If we more precise impact localization is required, the electrodes should be divided into more parts and impact data acquisition conducted in all the points of the electrode. In this paper, we developed a light, cheap and simple multi-channel data acquisition system to aid in data gathering. In total four channels data acquisition have been tested using the ARM Cortex-M3.