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Optical Fiber Sensors for Aircraft Structural Health Monitoring.

García I, Zubia J, Durana G, Aldabaldetreku G, Illarramendi MA, Villatoro J - Sensors (Basel) (2015)

Bottom Line: Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors.Several practical applications for structures and engines we have been working on are reported in this article.With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

View Article: PubMed Central - PubMed

Affiliation: Department of Communications Engineering, E.T.S.I. of Bilbao, University of the Basque Country UPV/EHU, Alda. Urquijo s/n Bilbao 48013, Spain. iker.garciae@ehu.eus.

ABSTRACT
Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

No MeSH data available.


Related in: MedlinePlus

(a) Ideal behavior of the reflected spectrum of an FBG subjected to a longitudinal strain; (b) Effect of a transverse stress on the reflected spectrum of the FBG. In all figures the blue line represents the non-perturbed spectrum of the FBG and the red one is the spectrum after the application of the load.
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sensors-15-15494-f002: (a) Ideal behavior of the reflected spectrum of an FBG subjected to a longitudinal strain; (b) Effect of a transverse stress on the reflected spectrum of the FBG. In all figures the blue line represents the non-perturbed spectrum of the FBG and the red one is the spectrum after the application of the load.

Mentions: Thus, it is clearly seen that the Bragg wavelength presents a cross-sensitivity phenomenon (it is sensitive to both temperature and strain). For strain measurements, the effect of temperature has to be compensated. Different configurations have been reported for this purpose [32,33,34,35,36,37,38,39,40,41,42,43,44]. However, when temperature gradients in the structure are not excessive, the use of a single FBG insulated from the effect of the strain is enough to compensate the effect of temperature in the rest of the FBGs, thus allowing us to discriminate the variations in the Bragg wavelength that appear as a consequence of strain. FBGs are excellent strain sensors when the load is applied in the axial direction of the sensor. In this situation, the FBG only undergoes contraction or elongation. If there is a transverse stress applied, the fiber presents birefringence due to the variation experienced by the effective refraction index on each propagation axis [45]. As a consequence, the grating exhibits two different Bragg conditions, and the approximately Gaussian-shaped reflected spectrum of the FBG splits into two peaks, as represented in Figure 2 [46]. Another similar phenomenon appears when there is a non-uniform strain field, because, in this case, the spectrum is broadened and even split into several peaks [20], which makes it difficult to track the Bragg wavelength. Both problems can arise when the FBG is embedded in composite materials. In conclusion, FBGs constitute a mature technology and compared to strain gauges, provide multiple benefits and attractive properties, such as multiplexing capability, the possibility of being embedded in the structure, long term stability and a competitive cost per channel. Nevertheless, some issues, like non-uniform or multidirectional complex strain conditions and the lack of aircraft certification must be solved, so that FBGs can be used in SHM systems for aircraft structures.


Optical Fiber Sensors for Aircraft Structural Health Monitoring.

García I, Zubia J, Durana G, Aldabaldetreku G, Illarramendi MA, Villatoro J - Sensors (Basel) (2015)

(a) Ideal behavior of the reflected spectrum of an FBG subjected to a longitudinal strain; (b) Effect of a transverse stress on the reflected spectrum of the FBG. In all figures the blue line represents the non-perturbed spectrum of the FBG and the red one is the spectrum after the application of the load.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4541841&req=5

sensors-15-15494-f002: (a) Ideal behavior of the reflected spectrum of an FBG subjected to a longitudinal strain; (b) Effect of a transverse stress on the reflected spectrum of the FBG. In all figures the blue line represents the non-perturbed spectrum of the FBG and the red one is the spectrum after the application of the load.
Mentions: Thus, it is clearly seen that the Bragg wavelength presents a cross-sensitivity phenomenon (it is sensitive to both temperature and strain). For strain measurements, the effect of temperature has to be compensated. Different configurations have been reported for this purpose [32,33,34,35,36,37,38,39,40,41,42,43,44]. However, when temperature gradients in the structure are not excessive, the use of a single FBG insulated from the effect of the strain is enough to compensate the effect of temperature in the rest of the FBGs, thus allowing us to discriminate the variations in the Bragg wavelength that appear as a consequence of strain. FBGs are excellent strain sensors when the load is applied in the axial direction of the sensor. In this situation, the FBG only undergoes contraction or elongation. If there is a transverse stress applied, the fiber presents birefringence due to the variation experienced by the effective refraction index on each propagation axis [45]. As a consequence, the grating exhibits two different Bragg conditions, and the approximately Gaussian-shaped reflected spectrum of the FBG splits into two peaks, as represented in Figure 2 [46]. Another similar phenomenon appears when there is a non-uniform strain field, because, in this case, the spectrum is broadened and even split into several peaks [20], which makes it difficult to track the Bragg wavelength. Both problems can arise when the FBG is embedded in composite materials. In conclusion, FBGs constitute a mature technology and compared to strain gauges, provide multiple benefits and attractive properties, such as multiplexing capability, the possibility of being embedded in the structure, long term stability and a competitive cost per channel. Nevertheless, some issues, like non-uniform or multidirectional complex strain conditions and the lack of aircraft certification must be solved, so that FBGs can be used in SHM systems for aircraft structures.

Bottom Line: Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors.Several practical applications for structures and engines we have been working on are reported in this article.With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

View Article: PubMed Central - PubMed

Affiliation: Department of Communications Engineering, E.T.S.I. of Bilbao, University of the Basque Country UPV/EHU, Alda. Urquijo s/n Bilbao 48013, Spain. iker.garciae@ehu.eus.

ABSTRACT
Aircraft structures require periodic and scheduled inspection and maintenance operations due to their special operating conditions and the principles of design employed to develop them. Therefore, structural health monitoring has a great potential to reduce the costs related to these operations. Optical fiber sensors applied to the monitoring of aircraft structures provide some advantages over traditional sensors. Several practical applications for structures and engines we have been working on are reported in this article. Fiber Bragg gratings have been analyzed in detail, because they have proved to constitute the most promising technology in this field, and two different alternatives for strain measurements are also described. With regard to engine condition evaluation, we present some results obtained with a reflected intensity-modulated optical fiber sensor for tip clearance and tip timing measurements in a turbine assembled in a wind tunnel.

No MeSH data available.


Related in: MedlinePlus