Temperature and Strain Measurements With Fiber Bragg Gratings Embedded in Stainless Steel 316

Single-mode optical fibers with thin nickel coatings (outer diameter similar to 350 mu m) are successfully embedded into stainless steel (SS) 316 components using bespoke laser-based additive manufacturing technology. In our approach, we manufacture SS 316 components using selective laser melting, incorporating U-shaped grooves with dimensions suitable to hold nickel-coated optical fibers. Coated optical fibers containing fiber Bragg gratings for strain monitoring and temperature sensing are placed in the groove. The embedding is completed by melting subsequent powder layers on top of the fibers. Cross-sectional microscopy analysis of the fabricated components, together with analysis of the Bragg gratings behavior during fabrication indicates a strong substance-to-substance bond between coated fiber and added SS 316 material. Temperature and strain cycling of the embedded sensors demonstrates the ability of gratings to survive the embedding process, and act as sensing elements in harsh environments. In situ strain and temperature measurements from within the component are demonstrated for high dynamic stress levels and elevated temperatures (<400 degrees C).