Degree Type

Dissertation

Date of Award

2005

Degree Name

Doctor of Philosophy

Department

Aerospace Engineering

First Advisor

Lester W. Schmerr, Jr.

Abstract

In this work ultrasonic models and measurements are used to characterize a number of the important elements of an ultrasonic measurement system as well as the entire system. Ultrasonic measurement models for predicting the response from reference reflectors are described, including a new ultrasonic measurement model recently developed to simulate the ultrasonic response of an infinitely long cylindrical cavity. The reference reflectors considered include spherical pores, flat-bottom holes and side-drilled holes, which are commonly used in nondestructive evaluation studies. These reflectors are employed in a series of modeling/experimental studies to assess where approximate and more exact scattering models are needed and to estimate the significance of beam variations over the reflector surface. Model-based simulated flaw responses are compared to experimentally determined flaw responses from these reference reflectors and the accuracy of the models is discussed.;The role that an ultrasonic piezoelectric transducer plays in an ultrasonic measurement system can be described in terms of the transducer's input electrical impedance and its sensitivity. A new model-based method for simultaneously determining the impedance and sensitivity of commercial ultrasonic immersion transducers is developed. This method is based on a pulse-echo setup and relies only on electrical measurements. It is demonstrated that sensitivities obtained with this new method agree well with the sensitivities obtained using a more complex three-transducer method originally developed for lower-frequency acoustic transducers that has been used in many previous studies. The influence of the pulser/receiver settings on the transducer electrical impedance and sensitivity is also discussed. Cabling effects present are compensated for in the new pulse-echo method.;The transducer impedance and sensitivity measurements obtained using this new pulse-echo method are combined with measurements/models for all the other electrical elements in an ultrasonic measurement system to determine a system transfer function that characterizes the effect of all the electrical and electromechanical components in the system. It is shown that by combining the system transfer function with models of the acoustic/elastic process present in a measurement system it is possible to accurately simulate the output voltage of the entire ultrasonic measurement system.

DOI

https://doi.org/10.31274/rtd-180813-11463

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Ana Lilia Lopez-Sanchez

Language

en

Proquest ID

AAI3184635

File Format

application/pdf

File Size

139 pages

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