Design and Development of Fiber Bragg Grating Sensor Devices for Aerospace Applications

Abstract

Optical sensors are becoming increasingly popular and gradually replacing electrical sensors due to their faster response, higher sensitivity, immunity to electromagnetic interference and electrical sparking. The advancements in fiber-optic telecommunication systems, have led to the development of fiber-optic sensors to integrate optoelectronic devices and fiber-optic telecommunication components. This has tremendously reduced the cost of optical fibers and its related components. Fiber Bragg Grating (FBG) sensors are one of the most widely used types of fiber optic-based sensors due to their multi-parameter sensing capability and wavelength-encoded output which is independent of input light intensity fluctuations. FBG sensors are inherently sensitive to strain and temperature but can be modified to measure other physical parameters. They have been used in a multitude of applications such as bio-medical, civil engineering, chemical detection, marine engineering, structural health monitoring of aircraft composites, etc. In this thesis, we explore their potential for measurement of different parameters in aerospace applications. This Ph.D. dissertation work explores the development of FBG sensors for aerospace engineering applications, especially in ground based aerodynamic test facilities. FBG sensors have been used to design and develop novel sensor systems/probes for applications in supersonic ejector/jet facilities and impulse test facilities like shock tubes. Multiple parameters such as strain, pressure and temperature have been measured using FBG sensors in ground-based aerodynamic test facilities. Experimental results have been compared with conventional piezoelectric and piezoresistive sensors. Further, detailed analyses of the measured parameters are carried out to validate the experimental results of respective test facilities with simulation studies using COMSOL Multiphysics and ABAQUS numerical analysis tools. A concise summary of the work carried out in the thesis is presented below: For space applications, a diaphragm based FBG pressure sensor has been developed to measure high pressures up to 700 bar of cryogenic propellants as well as pneumatic pressure in rockets, missiles, and launch vehicles. The pressure sensor is compensated for a wide temperature range (-400C to 900C) to suit space conditions. FEM analysis of the sensor assembly has been carried out. The experimental results are validated with thermal and FBG strain transfer analysis using COMSOL Multiphysics. The dynamic pressure sensing capability of the diaphragm based FBG high-pressure sensor is tested using a shock tube facility. The stability and reliability of the sensor in vibration environments are studied using an electrodynamic shaker. For flow parameter measurement in a ground-based high-speed aerodynamic test facility, an FBG-based sensor setup has been designed and developed for simultaneous measurement of wall static pressure and temperature in a supersonic ejector facility. A pressure insensitive FBG temperature probe is developed for both temperature measurement and temperature compensation of FBG pressure sensor. The FBG pressure measurements are validated against a standard piezoresistive pressure sensor. Fluid-structure interaction simulation is carried out using COMSOL Multiphysics to understand the flow interactions with the fiber. In the next work, the use of FBG sensors for measuring blast wave-induced dynamic strain in aerospace-grade polymer materials has been demonstrated inside a Vertical Shock Tube (VST) which is an aerodynamic impulse test facility. A detailed experimental study is carried out with blast waves of different peak pressures generated inside VST. The strain responses of the two polymer samples namely, polypropylene and polytetrafluoroethylene, to different blast pressure amplitudes are recorded using FBG sensor. The material responses to blast wave impact are studied and compared using FFT and time-frequency analyses. The rise time and working frequency of FBG sensor are studied to verify the feasibility of FBG sensors for blast wave measurements. FEM analysis of the strain response of the two polymer samples to blast wave is carried out to validate the FBG strain measurement experiments. The last work describes the design and development of FBG pressure sensor probe for monitoring blast waves in a shock tube environment. The FBG pressure sensor probe is developed to have high pressure and harsh environment withstanding capability as well as compatibility for mounting on the shock tube. The FBG blast pressure measurements are validated against that of a standard piezoelectric (PCB) pressure sensor. Air blasts of different magnitudes ranging from low to high pressures are measured using an FBG sensor. The pressure time histories of FBG and PCB sensors are compared and verified. Time-frequency analysis of the pressure signals is carried out to study the dynamics of blast waves. Further, FBG sensor utility to measure dynamic pressure in a granular medium like sand column subjected to blast impact inside a shock tube is demonstrated for potential applications in blast protective sand barrier systems.