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Title:Nonlinear ultrasonic testing using a non-collinear approach: application to heat treatment of steels and to asphalt concrete mixtures
Author(s):Price, Nathan
Advisor(s):Reis, Henrique M.
Department / Program:Industrial&Enterprise Sys Eng
Discipline:Systems & Entrepreneurial Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Non-Collinear Wave Mixing
Nonlinear Ultrasonic Testing
Nondestructive Evaluation
Heat Treatment
Acoustic Velocity Measurements
Abstract:Tests were performed to investigate micro-structural dependence of acoustic wave attenuation, velocity, and a non-linear parameter, non-collinear scattered wave amplitude. Specimens of various microstructures were prepared by means of heat treatment for 1045 and 4140 Steel. Nonlinear investigation was also performed on two asphalt specimens exposed to different aging conditions. Specimens made of 1045 Steel with various crystalline compositions were used as torsional wave guides in order to observe acoustic attenuation behavior. Bars of one eighth inch diameter and 15 inches in length were heated to austenization temperature and cooled at various rates in order to produce diverse microstructures. Cooling rates were varied by means of water quenching, oil quenching, air cooling, and oven cooling. Torsional acoustic waves were excited in through transmission for each bar, and the acoustic attenuation was obtained by fitting exponential curves to the maximum amplitude peaks of the first three reflected time signals. Attenuation values were obtained, compared, and discussed. The general trend showed increased attenuation coefficients with decreasing cooling rate. It is noted that water quenched bars, containing Martensite, demonstrated distinctly different behavior than the other tested specimens. All water quenched bars exhibited wave modes not predicted theoretically and absent from the time signals of specimens of all other cooling rates. This was due to a lack of symmetry during the cooling process, which led to guided-wave mode-conversion. Relevant carbon steel heat treatment and guided wave propagation theory is also presented to provide background. Rectangular bar specimens composed of 4140 Steel were exposed to five different cooling rates. Shear and longitudinal velocities were then measured using cross-correlation of back wall echoes. It was found that wave velocity increased with decreasing cooling rate for both shear and longitudinal waves for all heat treatments. Two different non-collinear wave mixing conditions (the mixing of two shear waves and two longitudinal waves) were then tested on 4140 specimens. No identifiable scattered wave was detected in either configuration. Investigation of non-collinear longitudinal wave mixing was also conducted on two asphalt specimens to evaluate the feasibility of estimating binder oxidation, i.e., aging. A range of interaction frequencies was used and maximum amplitude of the scattered wave frequency was identified for a frequency relationship. The amplitudes of the scattered wave amplitudes were then corrected for material attenuation at the excited frequencies. It was observed that a non-collinear approach can be used to estimate the level of aging in asphalt concrete mixtures.
Issue Date:2012-05-22
Rights Information:Copyright 2012 Nathan Price
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05

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