Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Mechanical Engineering

Major Professor

Rasim Guldiken, Ph.D.

Committee Member

Julianne Harmon, Ph.D.

Committee Member

Ajit Mujumdar, Ph.D.

Committee Member

Kyle Reed, Ph.D.

Committee Member

Andres Tejada-Martinez, Ph.D.

Keywords

Attenuation, Finite Element Analysis, Leaky Rayleigh Wave, Solid Surface, Ultrasonic Waves

Abstract

In this dissertation, two separate applications that are related to surface acoustic waves in a solid media are presented. The first study concerns simulating and validating an experimentally study for quantifying the bolt tension in the bolted joints using the surface acoustic wave. The second study experimentally investigates measuring the level of a liquid existing on a solid surface via surface acoustic waves and exploring the effect of liquid existence on the propagation of surface acoustic waves over the solid surface.

Quantifying bolt tension and ensuring that bolts are appropriately tightened for large-scale civil infrastructures are crucial. This study investigates the feasibility of employing the surface acoustic wave (SAW) for quantifying the bolt tension via finite element modeling. The central hypothesis is that the real area of contact in a bolted joint increases as the tension or preload is increased, causing an acoustical signature change. The bolted joints was modeled using a Computer Aided Design Software and the simulation was carried out via Finite Element Analysis software (ANSYS18.1).The experimentally verified 3-D simulations were carried out in two steps: A preload was first applied to the bolt body to simulate the realistic behavior of bolted joints, and the SAW propagation was then excited on the top surface of the plate to reflect from the bolt. The bolt tension value was varied between 4 and 24 kN (properly tightened bolt) in the steps of 4 kN to study the effect of the bolt tension. The results indicate an increased reflected wave amplitude and a gradual phase shift, up to 0.5 µs, as the bolt tension increased. Furthermore, the result shows that the distance between the first reflected wave and the source becomes shorter as the preload increases, as hypothesized. A 1.9 mm difference in the distance between the maximum and minimum preload was observed. As part of this study, the simulation results were also compared with the experimental results, and a good agreement between the simulation and experiments was demonstrated.

The propagation of surface acoustic waves over a solid plate is highly influenced by the presence of liquid media on the surface. At the solid-liquid interface, a leaky Rayleigh wave radiates energy into the liquid, causing a signification attenuation of the surface acoustic wave amplitude. In this study, we take advantage of this spurious wave mode to predict the characteristics of the media, including the volume or height. In this study, the surface acoustic waves were generated on a thick 1018 steel surface via a 5 MHz transducer coupled through an angle beam wedge. A 3D-printed container was inserted on the propagation path. The pulse-echo time-domain responses of the signal were recorded at five different volumes (0, 400, 600, 1000, and 1800 µL). With the aid of parametric Computer Aided Design Software, both the position and distance of the entire traveling wave in the liquid layer were modeled and verified with experimental studies. The results indicated that the average drop in the reflected wave amplitude due to liquid loading is −62.5% compared to the empty container, and a percentage of error in height estimation was within 10% for all cases. Furthermore, no shift on the arrival time of the reflected wave from the defect (edge) was observed due to the liquid loading. Finally, the localized-time frequency components of the reflected wave were obtained via a Short-Time Fourier Transform technique using MATLAB software. A noticeable reduction in the central frequency was observed due to the liquid volume increasing. The method discussed herein could be useful for many applications, where liquid’s parameters or the ultrasonic wave behavior in the liquid need to be assessed.

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