Structural Compatibility and Fatigue Life of Integrated Optical Fiber Sensors for Helicopter Rotor Blades

This work evaluates the long-term fatigue life and structural compatibility of integrated optical fiber sensors (OFS) within an H145 (or BK117 D-3) helicopter flexbeam. Utilizing fiber Bragg grating (FBG) arrays, the study compares different deployment techniques under a 100,000-cycle fatigue test: embedded, surface-integrated, and surface-applied. A validated three-dimensional (3D) finite element model (FEM) was developed to reconstruct cross-sectional loads and correlate experimental strain data. Validation against conventional electrical strain gauges (SG) confirms that embedded FBGs significantly outperform SGs in durability, maintaining functionality beyond the operational limit of traditional sensors. Furthermore, the methodology successfully tracks global stiffness evolution and degradation throughout the fatigue life. Micro-computed tomography (µCT) scans verify that the integrated fibers do not compromise structural integrity. These findings demonstrate the potential of embedded OFS for continuous, in-service load monitoring and condition-based maintenance (CBM) of flight-critical rotorcraft components.