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

Abstract

This paper reports on research work which is a comprehensive study involving the design of an extrinsic Fabry–Perot interferometric strain sensor (EFPI-SS), the manufacture of smart carbon/epoxy beams preconditioned with artificial delamination, and the testing of these beams in three-point bending. A loading applied to the beams was quasi-static in nature and this was selected in order to facilitate the accurate and reliable control of the beam deformations. The EFPI-SSs were validated for their sensing capacity and survivability via surface mounting and interior embedment. Artificial delaminations of two different sizes were embedded within the host beams to simulate damage. Their effect on the bending stiffness induced by quasi-static loading was examined using the embedded EFPI-SSs along with surface-mounted conventional strain gauges (SGs) on a comparative basis. A linear response was obtained from the EFPI-SSs up to a strain level of 0.5%, and this was in good agreement with interpolated strains as well as those from analytical prediction. It was shown that the embedded EFPI-SSs were able to differentiate the effect of the tensile delaminations on the bending stiffness when the level of strain was substantial. It was noted that the interior strain data from the EFPI-SSs in conjunction with the surface SG data were very useful for extrapolating the strain difference on both sides of the delaminations, so that the possibility of delamination propagation could be deduced.

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