In this work the superior fatigue performance of surface bonded optical fiber is compared to conventional foil gages.

The ability to make numerous, distributed measurements in a single, standard optical fiber makes fiber-optic sensing a practical and financially attractive alternative to conventional methods. Our technique for high resolution distributed fiber-optic strain sensing is based on measuring spectral shifts in the Rayleigh backscatter along an optical fiber. High-sensitivity Optical Frequency Domain Reflectometry (OFDR) is used to measure the scatter continuously along the fiber with sub-cm spatial resolution. In this work, the performance of surface-bonded, low bend loss, polyimide coated optical fiber sensors during high-strain fatigue tests is reported. The sensors were applied to fiberglass coupons subjected to a +/-4000μstrain cyclic load. All fiber optic sensors survived the fatigue tests and demonstrated consistency in strain measurements. All resistive gages demonstrated cumulative zero-shift in microstrain early in the test cycle. These values increased in magnitude throughout the test cycle. The susceptibility of strain gages to fatigue damage when strained cyclically at high amplitudes limits its suitability for high-cycle monitoring. Subsequently, superior fatigue characteristics of fiber optic strain sensors paves the way for overcoming this limitation and supports its use for fatigue testing and other high-strain cyclic monitoring.

N. A. A. Rahim et. al., "Superior Fatigue Characteristics of Fiber Optic Strain Sensors," Aircraft Structural Integrity Program Conference (ASIP), San Antonio, Tx, 2012.