Monitoring of aeronautical composites with embedded FOBG sensor: Part I—Manufacturing and strain response under incremental fatigue loading spectrum

Carbon fiber-reinforced plastics were manufactured with embedded fiber optic Bragg grating (FOBG) sensors for strain monitoring purposes. A novel manufacturing concept was applied to decrease the possibility to induce damage on the ingress/egress point of the fiber to the laminate structure. Specimens without embedded sensors were manufactured as well, and quasi-static mechanical tests showed that FOBG embedding did not decrease the tensile mechanical properties. Coupons with embedded fiber were tested under different loading spectrum (ranging from 20% and up to 60% of ultimate tensile strength), and the differences between the loadings of the surface-attached strain gauge and the embedded sensor were less than 2.0% and for all the applied peak loads. Application of 65,000 fatigue cycles on several coupons was assessed to simulate the fatigue loading of the coupons over their life span. The already fatigued coupons were tested at the same loading spectrum, and their strain measurements were compared against the respective loading spectrum without prior fatigue. The differences at peak loads were less than 1.0%, and therefore, it can be assumed that fatigue damage after65,000 cycles was not accumulated in the sensing area of the Bragg grating sensor. To this end, the investigated FOBG embedding procedure and the proposed manufacturing methodology do not impose damage on the laminate composite.