Simultaneous interferometric and polarimetric strain measurements on composites using a fiber-optic strain gauge

A fiber-optic Michelson interferometer is used for remote sensing of the bending-induced surface strain (up to 2500 microepsilon) of plates made from carbon-fiber composites. The double-polarization method is used for eliminating the ambiguity of fringe counting. Simultaneous measurement of the birefringencedependent phase offset yields an additional analog (polarimetric) signal, which allows for initialization of the incremental readout. The measured dependence of surface strain on plate bending agrees with the theoretically expected linear relationship, and it agrees with the gauge sensitivity published by Valis et al. [Proc. Soc. Photo-Opt. Instrum. Eng. 1170, 495 (1989)]. The observed hysteresis and temperature sensitivity are significantly smaller than the same effects in an electrical strain gauge.