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Elastic wave assessments of thermal protection systems with linear and nonlinear waveguides

Thermal protection systems are specialized material systems that protect underlying structures from high thermal loads. Breakdown of a TPS can lead to propagating and sometime catastrophic failures of the underlying structures. As such, there is interest in developing in situ methods of evaluating the condition, performance and health of a TPS. This presentation will describe results from a series of studies aimed at developing methods of monitoring TPS systems nominally designed for hypersonic vehicles using elastic waves. A practical issue is that piezoelectric transducers are not able to withstand the high temperatures that can arise in and on the backside of a TPS. A workaround is to place a transducer in a cooler environment and to use a waveguide to transmit elastic wave information back and forth from the TPS to the transducer. This allows for both acoustic emission and ultrasonic transmission methods. One approach is to use a high-fidelity linear waveguide, such as a straight metal rod. Acoustic emission experiments with a linear waveguide indicate that the elastic waves produced during high thermal loading contain broadband frequency content. Statistical pattern recognition methods can tease out different loading conditions. An alternative method is to use a ball chain nonlinear waveguide to transmit and receive specific elastic waves that correspond to conditions of interest in the TPS. Experiments using ball chain waveguides to transmit and receive waves to a TPS will be presented along with numerical simulations of design procedures.

Author(s):

Dryver Huston    
University of Vermont
United States

Jonathan Razinger    
University of Vermont
United States

Stephen Pearson    
University of Vermont
United States