Cure monitoring of Boeing 737 test-bed fuselage skin composite repair using optical fibers sensing technique

This paper presents a cure monitoring process and service experience of a co-cured bonded composite patch repair applied to a damage on a Boeing 737 fuselage skin. This repair was applied in a location where no standard SRM repair could be adopted. Therefore, to ensure the quality and robustness of the repair, its application process was monitored by embedded fiber- optic Bragg sensors in real time. Such a sensing concept provides real time monitoring of the temperature distribution over the entire patch during the curing process. It also follows the development of the anticipated residual strains, which are induced, for a successful bonding of the composite patch to the aluminum substrate, by the mismatch between the thermal expansion coefficients of the two materials. Tracking these two parameters ensures proper temperature distribution at high spatial resolution, over the entire repair, combined with a quantitative assessment of the structural strength of the bond via the evaluation of the residual strains.