SMART STRUCTURAL MATERIALS WITH EMBEDDED FIBER OPTIC SENSORS FOR HEALTH MONITORING IN HARSH ENVIRONMENTS

Structural health monitoring is critical for components working in harsh environments to assessing their safety and integrity. This can be realized with advanced sensors, such as fiber optic sensors, embedded in these components. Recent studies have explored the use of ultrasonic additive manufacturing and laser-based additive manufacturing for fiber embedment. Fiber embedding using these techniques has been challenging for high-temperature materials commonly used in extreme environments, resulting in large gaps and voids around the embedded fiber. A good fiber-matrix bond is critical to guarantee free gas/liquid leaks as well as good temperature sensing and strain coupling. To this aim, this study proposed a novel fiber embedding technique using electric field-assisted sintering (EFAS). Sapphire fibers with a diameter of 125 mu m and length of 55 mm were placed in SS316L powder, which was subsequently sintered using EFAS. To optimize the processing parameters for fiber embedment, a parametric study was scoped. The as-fabricated samples were first examined using optical transmission testing to inspect fiber integrity. After that, the samples were cross-sectioned for microscopy analysis to evaluate the quality of bond between the embedded fiber and the matrix. The density, microstructure, and hardness of the sintered SS316L were also studied to optimize EFAS parameters. The result shows that intact sapphire fibers can be embedded in high-density SS316L with good metallurgical bonds using the optimized EFAS parameters. Optical transmission inspection demonstrates the successful transmission of light through the embedded fibers.