• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.172-175
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• 2005

The numerical simulation is performed for the acoustic emission and the wave propagation due to fiber breakage in single fiber composite plates by the finite element transient analysis. The acoustic emission and the following wave motions from a fiber breakage under a static loading is simulated to investigate the applicability of the explicit finite element method and the equivalent volume force model as a simulation tool of wave propagation and a modeling technique of an acoustic emission. For such a simple case of the damage event under static loading, various parameters affecting the wave motion are investigated for reliable simulations of the impact damage event. The high velocity and the small wave length of the acoustic emission require a refined analysis with dense distribution of the finite element and a small time step. In order to fulfill the requirement for capturing the exact wave propagation and to cover the 3-D simulation, we utilize the parallel FE transient analysis code and the parallel computing technology.

• Smart Structures and Systems
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• 제11권2호
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• pp.185-197
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• 2013

We developed a simultaneous strain measurement and damage detection technique using a pair of surface-mounted piezoelectric transducers and a fiber connecting them. This is a novel sensor configuration of the fiber acoustic wave (FAW) piezoelectric transducer. In this study, lead-zirconate-titanate (PZT) transducers are installed conventionally on a plate's surface, which is a technique used in many structural health monitoring studies. However, our PZTs are also connected with an optical fiber. A FAW and Lamb wave are simultaneously guided in the optical fiber and the structure, respectively. The dependency of the time-of-flight of the FAW on the applied strain is quantified for strain sensing. In our experimental results, the FAW exhibited excellent linear behavior and no hysteresis with respect to the change in strain. On the other hand, the well-known damage detection function of the surface-mounted PZT transducers was still available by monitoring the waveform change in the conventional Lamb wave ultrasonic path.

• 한국통신학회:학술대회논문집
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• 한국통신학회 1983년도 추계학술발표회논문집
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• pp.44-47
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• 1983

Through intensity modulation induced by micro bending of an optical fiber, a sensor detects the pressure and frequency of acoustic wave has been implemented. Axial slots on the cylinder suface with a period of 5.5 mm induce efficient microbending of the fiber, and a rubber sleeve covering the fiber enhances the fiber. Compared with a conventional hydrophone, it has a low minimum detectable pressure and can detect acoustic wave in 100Hz - 2KHz range.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.169-174
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• 2006

The outstanding mechanical property of optical fiber and the merits of acoustic emission sensing technique are unified for novel sensor system. The generated ultrasonic wave from piezoelectric generator are propagated along the optical fiber and also sensed. The propagated wave can be influence by external pressure on the optical fiber or environmental circumstance. The optical fiber sensor using ultrasonic wave has advantages compare with existing sensor system. In this study, the sensitivity of the optical fiber sensor is experimentally investigated. As the applications of the optical fiber sensor system using piezoelectric ultrasonic waves, the point load on the optical fiber is measured and the monitoring system for the void fraction of two phase flows is developed. The experimental results show the linear relationship between sensed voltage and void fraction.

• The Journal of the Acoustical Society of Korea
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• 제21권1E호
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• pp.25-30
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• 2002

We report on the development of a fiber optic hydrophone consists of a sensing Michelson interferometer and a compensating Mach-Zehnder interferometer for optical path length compensation. The double interferometer configuration has the following advantages: the hydrophone can be made more small; a laser source with a relatively short coherence length can be used; and the compensating interferometer can be located near the signal processing electronics, far away from the sensing interferometer and noise introduced by reference arm can be greatly reduced. The performance of the hydrophone is evaluated experimentally by immersing the sensing interferometer in a water tank to detect underwater acoustic signals generated by an acoustic wave projector. Experimental results show that over the frequency range of 1 to 4 kHz, the hydrophone has an almost flat response with an average normalized sensitivity of -302 dB re 1/ μ Pa.

• 한국광학회:학술대회논문집
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• 한국광학회 2008년도 동계학술발표회 논문집
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• pp.151-152
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• 2008

• Smart Structures and Systems
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• 제18권3호
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• pp.471-484
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• 2016

Optical fiber sensors have been proven that they have the potential to detect high-frequency ultrasonic signals, in structural health monitoring field which generally refers to acoustic emission signals from active structural damages and guided waves excited by ultrasonic actuators and propagating in waveguide. In this work, the sensing properties of optical fiber sensors based on Mach-Zehnder interferometer were investigated in the metal plate. Analytical formulas were conducted first to explore the parameters affecting its sensing performances. Due to the simple and definable frequency component, the Lamb wave excited by the piezoelectric wafer was employed to study the sensitivity of the proposed optical fiber sensors with respect to the frequency, rather than the acoustic emission signals. In the experiments, according to above investigations, spiral shape optical fiber sensors with different size were selected to increase their sensitivity. Lamb waves were excited by a circular piezoelectric wafer, while another piezoelectric wafer was used to compare their voltage responses. Furthermore, by changing the excitation frequency, the tuning frequency characteristic of the proposed optical fiber sensor was also investigated experimentally.

• 한국항공우주학회지
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• 제36권1호
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• pp.57-61
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• 2008

광섬유 내의 Depolarized-GAWBS를 이용한 변형율 측정방식에서, 측정부에 2개의 검광자를 배치하는 광학계를 꾸밈으로써 편광조절이 불필요한 간단한 변형율 측정방법을 제안하였다. 또한, 광섬유 재킷의 유무가 측정정확도에 미치는 영향도 함께 알아보았다.

• 한국해양공학회지
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• 제16권2호
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• pp.67-71
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• 2002

Damage process of CFRP laminates was characterized by Acoustic Emission (AE). The main objective of this study is to determine if the sources of AE in CERP laminates could be identified from the characteristics of the waveform signals recorded during monotonic tensile test. The time history and power spectrum of each individual wave signal recorded during test were examined and classified according to their special characteristics. The wave from and frequency of AE signal from a specimens is an aid to the determination of the extent of the different fracture mechanism such as matrix crack, debonding, fiber pull-out and fiber fracture as load is increased. Four distinct types of signals were observed regardless of specimen condition. The result showed that the AE method could be effectively used for analysis of fracture mechanism in CFRP laminates.

• 비파괴검사학회지
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• 제18권1호
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• pp.1-9
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• 1998

짧은 섬유로 강화된 열가소성수지의 복합재료를 대상 재료로 하여 AE의 발생위치(AE source location)를 구하고 AE신호의 진폭분포에 미치는 감쇠 손실(attenuation loss)의 영향을 정량적으로 검토했다. 모의 AE파를 이용하여 측정된 감쇠율은 시험편내의 섬유체적함유율의 증가에 따라 단순 선형관계식으로 예상되는 값보다 더 작았다. 시험편에서 계측된 AE진폭분포에 감쇠손실을 보정한 결과, 시험편의 게이지부에 설정된 각 구역에서 서로 유사한 수준의 진폭분포가 나타났다. 또한 보정된 AE진폭은 시험편의 변형이 진행됨에 따라 더욱 크게 되었다. 따라서, AE진폭을 이용한 고분자복합재료의 손상해석에서는 AE파의 감쇠효과를 보정해야 됨이 확인되었다.