Optical frequency domain reflectometry measurements in internally clad single crystal sapphire fiber have received attention in recent years due to their high temperature distributed sensing potential. As work with these fibers has proceeded, there have been some inconsistencies in the results. Deeper investigation and testing has identified two critical considerations for the proper functioning of these fibers. First, users must address the propagation of multimode light along the outer surface of the fiber. By observing the far-field image of an internally clad sapphire fiber when adding index matching fluid to the outer fiber surface, we demonstrate the effects of removing the higher order modes from these fibers. The addition of index matching fluid resulted in nearly single mode performance where multimode performance was previously observed. Second, users must address the effect that coupling the fiber to the interrogator via silica based fiber has on the internally clad sapphire fiber's performance. Direct fusion splicing of silica to sapphire, as has been used in the recent work with these fibers, has a mode filtering effect which can be beneficial towards the modal behavior of the fibers. However, in this paper we demonstrate that the splicing can cause a sensing failure due to little or no low order mode light, that is useful for sensing, returning to the detector. The positive results from recent years have demonstrated that optical frequency domain reflectometry sensing performance will be successful in clad sapphire fiber; but only when the considerations described herein are addressed properly.

This paper discusses the development, processing steps, and evaluation of a smart build-plate or baseplate tool for metal additive manufacturing technologies. This tool uses an embedded high-definition fiber optic sensing fiber to measure strain states from temperature and residual stress within the build-plate for monitoring purposes. Monitoring entails quality tracking for consistency along with identifying defect formation and growth, i.e., delamination or crack events near the build-plate surface. An aluminum alloy 6061 build-plate was manufactured using ultrasonic additive manufacturing due to the process’ low formation temperature and capability of embedding fiber optic sensing fiber without damage. Laser-powder bed fusion (L-PBF) was then used to print problematic geometries onto the build-plate using AlSi10Mg for evaluation purposes. The tool identified heat generation, delamination onset, and delamination growth of the printed L-PBF parts.

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.

Rocket propulsion test facilities and test articles are highly instrumented to enable a comprehensive analysis of performance and to ensure propulsion system risks are mitigated for spaceflight. There is room to improve upon traditional instrumentation to provide the data fidelity necessary for monitoring remote, hazardous, or inaccessible locations. To address this challenge, the SensePipe was conceived that can measure multiple fluid parameters. The proof-of-concept prototypes used high-definition fiber optic sensors that were embedded into a pipe wall using ultrasonic additive manufacturing. The resulting design creates an intrinsically safe, low-profile, non-intrusive set fluid parameter sensors. This work demonstrates static measurement capabilities for temperature between -192°C to 70°C and fluid pressures up to 20 MPa. Regression standard errors for temperature and pressure were less than 8.11Δ°C and 0.386 MPa.