Reliability of strain monitoring of composite structures via the use of optical fiber ribbon tapes for structural health monitoring purposes

In aerospace industry, a lot of effort has been focused on the practical implementation of optical fibers on composite subcomponents for health monitoring purposes during the service life of an aircraft. To this direction the fiber optic ribbon tapes (FORTs) concept was developed in order to ease the handling, the surface placement and the maintenance of such sensitive sensors. In this paper, we investigate the structural durability of this concept comparing two ways of mounting the FORT (co-bonding and secondary bonding) under fatigue loading conditions. Through long term fatigue tests and utilizing additional experimental (electrical strain gauges (ESG)), theoretical as well as numerical tools, it is concluded that the deviation of the experimentally measured strains using the FORT approach versus conventional ESG values are well within an error of maximum 6%. Moreover, they remain in this error bound for as much as 106 loading cycles, rendering FORTs a reliable solution for aerospace SHM. In the final part of the study, the effect of the FORTs placement on the stiffness of a structure is assessed through numerical analysis of the changes of the dynamic characteristics as well as the modal response of an aeronautical subcomponent representative of a wing front spar.