Extrinsic Fabry-Perot Interferometric Strain Sensors Research Articles

Evaluating damage in smart composite laminates using embedded EFPI strain sensors

Extrinsic Fabry-Perot interferometric (EFPI) strain sensors (SSs) were assessed for their sensing capacity and survivability via surface mounting and interior embedment in the carbon/epoxy beams. Artificial delaminations of two different sizes were used to simulate delamination. The embedded EFPI-SSs along with surface-mounted SGs were used to evaluate the effect of the delaminations on bending stiffness induced by quasi-static loading on a comparative basis. The linear responses of EFPI-SSs up to a bending strain of 0.5% were in good agreement with the interpolated strains of surface strain measurements. The embedded EFPI-SSs were able to differentiate the effect of the tensile delaminations on bending stiffness. The interior strain data from embedded EFPI-SSs were shown to be very useful to extrapolate the strain difference on both sides of the delaminations as well as deducing local stresses.

Evaluation of embedded optical fiber sensors in composites: EFPI sensor fabrication and quasi‐static evaluation

AbstractThis article reports on the fabrication and evaluation of extrinsic Fabry–Perot interferometric (EFPI) sensors when embedded in fiber‐reinforced composites and tested under quasi‐static tensile and compressive mechanical loading. The EFPI strain sensors were embedded in carbon fiber composite test specimens, and their performance was compared against a surface‐mounted extensometer and electrical resistance strain gauges. When the composite was subjected to quasi‐static tensile loading, the sensors failed around a strain level of 0.5%; under compressive loading, the sensors survived until the failure of the composite at 1.1% strain. The EFPI sensors used in this study were fabricated in‐house and the issues relating to fabrication are discussed in the context of their performance when embedded in composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

Damage evaluation of smart composite beams using embedded extrinsic Fabry–Perotinterferometric strain sensors: bending stiffness assessment

This paper reports on research work which is a comprehensive study involving the design ofan extrinsic Fabry–Perot interferometric strain sensor (EFPI-SS), the manufacture of smartcarbon/epoxy beams preconditioned with artificial delamination, and the testing of thesebeams in three-point bending. A loading applied to the beams was quasi-staticin nature and this was selected in order to facilitate the accurate and reliablecontrol of the beam deformations. The EFPI-SSs were validated for their sensingcapacity and survivability via surface mounting and interior embedment. Artificialdelaminations of two different sizes were embedded within the host beams to simulatedamage. Their effect on the bending stiffness induced by quasi-static loading wasexamined using the embedded EFPI-SSs along with surface-mounted conventionalstrain gauges (SGs) on a comparative basis. A linear response was obtained fromthe EFPI-SSs up to a strain level of 0.5%, and this was in good agreement withinterpolated strains as well as those from analytical prediction. It was shown that theembedded EFPI-SSs were able to differentiate the effect of the tensile delaminationson the bending stiffness when the level of strain was substantial. It was notedthat the interior strain data from the EFPI-SSs in conjunction with the surfaceSG data were very useful for extrapolating the strain difference on both sides ofthe delaminations, so that the possibility of delamination propagation could bededuced.

Single-crystal sapphire fiber-based strain sensor for high-temperature applications

Single-crystal sapphire fibers have a very high melting point (up to 2050°C), which renders them a very good candidate for sensing applications at a very high temperature. We present in this paper the recent work of developing single-crystal sapphire fiber extrinsic Fabry-Perot interferometric strain sensors based on the white-light interferometric spectrum demodulation technique. Prototype sapphire strain sensors were fabricated and tested at high temperatures up to 1004°C. The preliminary experimental results indicate that the sensors are promising to be used under high-temperature environments for making strain measurements with strain measurement resolution of 0.2-μ strain.

Multiple strain state measurements using conventional and absolute optical fiber-based extrinsic Fabry-Perot interferometric strain sensors

A modified design of the extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor to allow complete characterization of multicomponent strain fields is proposed. The novel EFPI includes a sensor head with two input fibers such that the respective interference pattern from the end face of the output multimode fiber are in quadrature. Any strain field possessing a component along the line joining the axes of the two fibers causes the initial phase difference to be modulated. The measured change in phase difference is employed to determine this transverse component of the strain field. Absolute, rather than differential measurements of strain are possible using the absolute EFPI sensing system. Applications of the modified sensor-head to smart materials and structures are discussed.