Date of Award
1-1-2025
Document Type
Thesis
Degree Name
M.S. in Physics
First Advisor
Joel Mobley
Second Advisor
Cecille Labuda
Third Advisor
Likun Likun Zhang
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
This research investigates the ultrasonic behavior of nanocomposite and polymer materials by evaluating the phase velocity and attenuation coefficient of 20% multi-walled carbon nanotube (MWCNT) reinforced composites and nylon. The primary goal of the work is to study longitudinal and shear wave propagation in both composite and homogeneous media. To achieve this, I used thru transmission techniques to collect data at multiple incident angles, including 0°, 30°, 35°, and 40° relative to the transmitting transducer.
I analyzed the acquired ultrasonic signals using both time-domain and frequency-domain techniques. In the time-domain approach, I measured the peak-to-peak time delay from gated waveforms to measure the signal velocity. In the frequency domain, I extracted phase spectra to compute frequency-dependent phase velocity and used magnitude spectra to determine the attenuation coefficient across the usable frequency bandwidth. The gated waveform technique effectively reduced background noise and allowed for the isolation of wave modes, for shear wave measurements at higher angles.
The results showed that the longitudinal phase velocity measured at normal incidence was significantly higher than that of shear modes. At higher angles, mode converted shear wave were analyzed and found to have significantly higher attenuation than longitudinal waves. In terms of materials, the MWCNT sample consistently exhibited higher phase velocity than nylon at all angles, which likely reflects its enhanced stiffness due to nanofiller reinforcement. Phase velocities derived from the phase spectra matched closely with those calculated from time-domain waveform analysis, demonstrating good consistency between the two methods.
Attenuation coefficients increased with frequency for all samples and showed higher values at greater incident angles. This trend was particularly prominent for shear waves in MWCNT at 35° and 40°, where higher material damping and energy loss were evident.
Overall, this study confirms that the ultrasonic response of MWCNT composites and nylon varies significantly with wave type. The strong agreement between spectral and waveform-based phase velocity estimation validates the robustness of the experimental setup and processing techniques. These findings contribute to the broader understanding of wave propagation and mechanical properties of nanostructured composites.
Recommended Citation
Sonia, Farhana Afrose, "A Study of The Ultrasonic Properties of Dispersive Materials" (2025). Electronic Theses and Dissertations. 3394.
https://egrove.olemiss.edu/etd/3394
GS-11