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Title:Phononic materials as ultrasonic filters in nondestructive evaluation measurements
Author(s):Smith, Elizabeth J
Advisor(s):Matlack, Kathryn H.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Phononic materials
nonlinear ultrasound
nondestructive evaluation
ultrasonic filtering
additive manufacturing
direct metal laser sintering
Abstract:Nonlinear ultrasound is a nondestructive evaluation method that is sensitive to microscopic material damage, which is highly desirable information to prevent failure of critical components. The damage is correlated to the second harmonics generated in a material by a sinusoidal signal. However, measurements of the second harmonic are difficult to distinguish from experimentally-induced nonlinearities and require careful calibrations that have limited them to laboratory measurements. The periodic nature of phononic materials can be engineered to induce frequency regions of reduced transmission, called band gaps. This work presents a method to use phononic materials as ultrasonic filters in nonlinear ultrasound measurements, to passively filter extraneous nonlinearities present in experiments. Phononic materials were designed through finite element studies to transmit an ultrasonic wave but forbid the propagation of its second harmonic. Phononic filters were fabricated with direct metal laser sintering, and experimentally characterized in the ultrasonic regime. Results show that the filters behave as passive low-pass filters, mitigating transmission above an ultrasonic cut-off frequency by four orders of magnitude. This cut-off frequency is controlled by the unit cell geometry of the phononic material. The influence of the additive manufacturing process on the frequency transmission of phononic material is modeled to explain discrepancies between simulation and experiments. An analytical model of second harmonic generation in phononic filters is presented, and nonlinear ultrasound measurements are conducted with and without a phononic filter. Experiments and the analytical model show that phononic filter removes extraneous signals from the experiments, therefore isolating the second harmonic generation in a material. The flexibility of the additive manufacturing process allows for filter designs to be tailored for desired frequency ranges and materials. This work demonstrates how phononic materials could be used to advance nonlinear ultrasound measurements to in situ measurements of critical components, and may be further developed as waveguides to interrogate components with complex geometries.
Issue Date:2020-07-24
Rights Information:Copyright 2020 Elizabeth J. Smith
Date Available in IDEALS:2020-10-07
Date Deposited:2020-08

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