A Fully Distributed Strain Rosette Using High Definition Fiber Optic Sensing

Integration of new materials into critical structures and applications has driven the need for using strain profiles to characterize material behavior, conduct structural health monitoring, and enable in-situ non-destructive evaluation to drive condition-based maintenance. Due to their small size, flexibility, and low weight, High-Definition Fiber Optic Sensors (HD-FOS) have been frequently utilized for highly spatially-resolved strain measurements with a sampling spacing of 0.65 mm on a wide variety of materials and complex part geometries. HD-FOS, like many fiber optic sensors, is primarily sensitive to strain along the length of the fiber, making it impossible to accurately determine principal and shear strains with a single straight sensor. This work demonstrates how a single fiber can be configured into a rosette geometry, allowing planar and shear strains to be fully characterized. New research has shown that by arranging a single fiber optic sensor in an extended rosette pattern, distributed principal strains and their orientations can be determined at any location within the pattern. This research focused on integrating fiber optic sensors into composite structures and culminated with embedding a distributed rosette pattern into a composite helicopter rotor blade. The rotor blade was shown to be effective in measuring distributed strains on the order of +/- 500 microstrain along its curved surfaces, resulting in a highly-desirable smart structure capable of measuring its own mechanical integrity.