Measurements of strain distributions with a long gauge FBG sensor using optical frequency domain reflectometry

Igawa, Hirotaka; Murayama, Hideaki; Kasai, Tokio; Yamaguchi, Isao; Kageyama, Kazuro; Ohta, Keiich

doi:10.1117/12.624250

Cited by 21 publications

(14 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Fourier transform of the signal sampled at the constant wavenumber interval provides the information on the position of each FBG in the array, and a narrow inverse Fourier transform at specific positions (frequencies) within this Fourier transform can then be used to recover the wavelength spectrum of a specific FBG. In the distributed measurement using OFDR we can easily map the strain profile along a long gauge FBG from a spectrogram given by Fourier transform analysis with a sliding window [10]. In this study we evaluated the spatial resolution and the sensitivity of this approach in distributed strain measurements from the results of simulations and experiments.…”

mentioning

confidence: 98%

Distributed Strain Measurement with High Spatial Resolution Using Fiber Bragg Gratings and Optical Frequency Domain Reflectometry

Murayama

Igawa

Kageyama

et al. 2006

Optical Fiber Sensors

View full text Add to dashboard Cite

High spatial resolution and sensitivity are required in distributed strain measurements for structural health monitoring. In this paper we show that the distributed strain measurements with the high spatial resolution can be implemented by optical frequency domain reflectometry (OFDR). We could easily map the strain profile along a long gauge FBG from a spectrogram by applying Fourier transform analysis with a sliding window to the signal obtained from the measurement system. The OFDR signal can be simulated by the transfer matrix method based on coupled mode theory. We evaluated the spatial resolution and the sensitivity from the results of simulations and experiments. We confirmed that the spatial resolution of the current system is about 4 mm and it may be changed according to the location of the grating in the sensing fiber. In addition, the strain distribution adjacent to holes of an aluminum tensile specimen was measured. The agreement between this experimental result and the simulated one was good. IntroductionDistributed measurements using fiber optic sensors attract the attention of researchers studying on structural health monitoring (SHM) systems, because they can effectively obtain useful information on the structural integrity all over a structure from those systems [1]. Fiber optic distributed strain sensors can provide the information on harmful deformation or stress concentration due to damage or an unexpected large load. In order to assess the structural integrity properly according to the strain/stress distributions obtained from the distributed strain sensors, it is important that the sensors can detect slight anomaly in the distributions [2]. Therefore, the high spatial resolution and the sufficient sensitivity are required in the measurement system.In recent years various techniques for distributed strain measurements have been proposed. Among them, the distributed sensing techniques based on Brillouin scattering have been developed by many researchers and have drawn attention in SHM fields [3,4]. While fiber Bragg grating (FBG) sensors with some interrogation systems are ordinarily employed for quasi-distributed strain or temperature measurements, they can be also applied to full-distributed sensing. If a strain distribution measured is monotonic, the strain profile along the grating can be determined by analyzing the reflection spectrum [5]. A strain distribution along a chirped grating is measured by the phase-based sensing method or the low-coherence reflectometry [6,7]. However, these distributed sensing methods have a drawback, such as elimination of uniform gratings or short sensing range. By using a tunable laser demodulation, the strain profile along a uniform grating with a long gauge length can be mapped based on Fourier transform analysis [8]. Although this sensing system can measure strain distributions with the high spatial resolution, it seems that signals outputted from several photodetectors in the sensing system have to be acquired individually and analyzed step by step.In t...

show abstract

mentioning

confidence: 98%

Distributed Strain Measurement with High Spatial Resolution Using Fiber Bragg Gratings and Optical Frequency Domain Reflectometry

Murayama

Igawa

Kageyama

et al. 2006

Optical Fiber Sensors

View full text Add to dashboard Cite

show abstract

“…This paper presents that resin flow monitoring during VaRTM can be implemented by the distributed sensing technique based on long gauge FBGs and OFDR [13][14]. Finally, we attempt to apply this system to cure monitoring and structural health of composite structure fabricated by VaRTM, because FBG responds to temperature and strain.…”

Section: Introductionmentioning

confidence: 98%

Resin flow monitoring in vacuum-assisted resin transfer molding using optical fiber distributed sensor

Eum

Kageyama

Murayama

et al. 2007

Behavior and Mechanics of Multifunctional and Composite Materials 2007

View full text Add to dashboard Cite

In this study, we implemented resin flow monitoring by using an optical fiber sensor during vacuum assisted resin transfer molding (VaRTM).We employed optical frequency domain reflectometry (OFDR) and fiber Bragg grating (FBG) sensor for distributed sensing. Especially, long gauge FBGs (about 100mm) which are 10 times longer than an ordinary FBG were employed for more effective distributed sensing. A long gauge FBG was embedded in GFRP laminates, and other two ones were located out of laminate for wavelength reference and temperature compensation, respectively. During VaRTM, the embedded FBG could measure how the preform affected the sensor with vacuum pressure and resin was flowed into the preform. In this study, we intended to detect the gradient of compressive strain between impregnated part and umimpregnated one within long gauge FBG. If resin is infused to preform, compressive strain which is generated on FBG is released by volume of resin. We could get the wavelength shift due to the change of compressive strain along gauge length of FBG by using short-time Fourier transformation for signal acquired from FBG. Therefore, we could know the resin flow front with the gradient of compressive strain of FBG. In this study, we used silicon oil which has same viscosity with resin substitute for resin in order to reuse FBG. In order to monitor resin flow, the silicon oil was infused from one edge of preform, the silicon oil was flowed from right to left. Then, we made dry spot within gauge length by infusing silicon oil to both sides of preform to prove the ability of dry spot monitoring with FBG. We could monitor resin flow condition and dry spot formation successfully using by FBG based on OFDR.

show abstract

“…The most important one was the lack of the spatial resolution [14]. So the authors have developed the sensing system to measure strain distribution with a high spatial resolution for a decade [15]. We have also applied the developed fiber-optic distributed sensor to load identification and damage detection in the field of SHM, especially for structures made of advanced composite materials [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Structural health monitoring by using fiber-optic distributed strain sensors with high spatial resolution

2013

View full text Add to dashboard Cite

In this paper, we review our researches on the topics of the structural health monitoring (SHM) with the fiber-optic distributed strain sensor. Highly-dense information on strains in a structure can be useful to identify some kind of existing damages or applied loads in implementation of SHM. The fiber-optic distributed sensors developed by the authors have been applied to the damage detection of a single-lap joint and load identification of a beam simply supported. We confirmed that the applicability of the distributed sensor to SHM could be improved as making the spatial resolution higher. In addition, we showed that the simulation technique considering both structural and optical effects seamlessly in strain measurement could be powerful tools to evaluate the performance of a sensing system and design it for SHM. Finally, the technique for simultaneous distributed strain and temperature measurement using the PANDA-fiber Bragg grating (FBG) is shown in this paper, because problems caused by the cross-sensitivity toward strain and temperature would be always inevitable in strain measurement for SHM.

show abstract

Measurements of strain distributions with a long gauge FBG sensor using optical frequency domain reflectometry

Cited by 21 publications

References 0 publications

Distributed Strain Measurement with High Spatial Resolution Using Fiber Bragg Gratings and Optical Frequency Domain Reflectometry

Distributed Strain Measurement with High Spatial Resolution Using Fiber Bragg Gratings and Optical Frequency Domain Reflectometry

Resin flow monitoring in vacuum-assisted resin transfer molding using optical fiber distributed sensor

Structural health monitoring by using fiber-optic distributed strain sensors with high spatial resolution

Contact Info

Product

Resources

About