Session: 17-01-01: Research Posters

Paper Number: 149841

149841 - Investigation of Fiber Optic Sensing of Strain and Temperature Fields in Hypersonic Structures 

The objective of this research effort is to develop a Fiber Bragg Grating sensor network which is capable of monitoring the strain, temperature and vibrational impact of aerothermodynamic effects on a structure's surface. The sensor network will collect data through an optical interrogation system powered with a tunable laser. The motivation for the project is to lay the foundations for a system which is capable of operating in a high temperature, extreme environment such as a hypersonic flow. The resulting FBG sensor network would open the door for active monitoring of aerodynamic structures and control surfaces during high-speed flight conditions. A finned plate structure where the fin forces a shock to impinge onto the square compliant panel's outer surface, was used as the hardware test article. Validation and verification of measurements is a core driver of the research conducted and the combination of experimental and simulation processes was key. Experimental results collected simultaneously from an electronic strain gauge data acquisition system, provide a baseline strain reading to calibrate FBG results. This comparison technique ensures accurate FBG measurements for strain and vibrations on the compliant panel surface. Fiber Bragg Gratings are optical fibers with a laser engraved grating which is sensitive to thermal and physical strain. Without any electrical components at the measurement site, the sensor is discrete and is not affected by electromagnetic disturbances from actuators or other systems. The Bragg wavelength of each individual FBG shifts due to the strain applied; the index of refraction of the Bragg grating is altered by changes at the site where the sensor is bonded. To design the network layout, in an effort to avoid the vibrational nodes of the panel, a simulated model of the complaint panel was used to complete modal analysis. The mode shapes of the six lowest resonant frequencies were observed and used as a guide to determine the optimum locations for placing individual FBG sensors. This ANSYS simulation was further supported with single point vibrometer experiments where the resonant frequencies were derived from excitations with an impact hammer. Using a Fast Fourier Transform and a Power Spectrum approach, individually, the experimental data for a damped harmonic oscillation on the compliant panel, was analyzed. The experimental results were compared between the two data analysis methods and validated against the simulated panel results. The methodology used leveraged the computational modeling tools at our disposal while supporting our simulation data with physical replica experiments of the modeled behaviors. The simulations provide the benefit of relying on low-cost high density surface data with low fidelity at any given individual point. While the experiments enhance confidence by providing high fidelity results at discrete points. For hypersonic vehicles the development of a hull-surface-monitoring-system would add the benefit of providing whole body performance data under extreme conditions. Flight control systems can benefit from in-flight, continuously sampled, material performance data and pilots can benefit from vehicle performance heuristics which can be added to the instrument panel of the cockpit. Overall, a surface monitoring sensor network would allow detailed flight tracking and confidence during complex maneuvers at high velocity.

Presenting Author: Rafael Meza University of Maryland, College Park

Presenting Author Biography: Rafael is a Colombian born engineering student from South Florida completing his first year of M.S. in Mechanical Engineering at the University of Maryland, College Park. He completed his B.S. in Mechanical Engineering at Florida State University in December of 2023. Rafael is exploring the field of Optical Interrogation focusing on systems with Fiber Bragg Grating sensors and their application to testing in hypersonic environments. At the Sensors and Actuators Lab at UMD he is advised by Dr. Miao Yu and Dr. Balakumar Balachandran.

Authors:

Rafael Meza University of Maryland, College Park
Miao Yu University of Maryland, College Park
Balakumar Balachandran University of Maryland, College Park