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

Abstract

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.