Non-contact Ultrasonic Technique Research Articles

Noncontact ultrasonic spectroscopy technique for the measurement of elastic moduli and ultrasonic attenuation of solids

A novel method and apparatus for measuring the elastic moduli and ultrasonic attenuation of small samples (millimeter dimensions) over a wide temperature range is described. In the most general case, a nonmagnetic sample is coated with a thin film of a magnetostrictive material. The film performs both as a driving transducer and as a receiving transducer. An alternating magnetic field of variable frequency generates a periodic stress in the film and drives the sample into mechanical resonances. The permeability of the film changes when the sample is resonating and allows the detection of the resonances. The operation of the system and the mathematical procedures to deduce the elastic moduli and ultrasonic attenuation are exemplified with measurements on amorphous and crystalline alloys. [Work supported by the U.S. Department of Energy.]

Analytical ultrasonics for characterization of metallurgical microstructures and transformations: Rosen, M. Analytical ultrasonics in materials research and testing. Proceedings of a conference, NASA Lewis Research Center, Ohio (United States), 13–14 Nov. 1984. pp. 83–102. NASA conference publication 2383 (1986)

The application of contact (piezoelectric) and noncontact (laser generation and detection) ultrasonic techniques for dynamic investigation of precipitation hardening processes in aluminum alloys, as well as crystallization and phase transformation in rapidly solidified amorphous and microcrystalline alloys is discussed. From the variations of the sound velocity and attenuation the precipitation mechanism and kinetics were determined. In addition, a correlation was established between the observed changes in the velocity and attenuation and the mechanical properties of age-hardenable aluminum alloys. The behavior of the elastic moduli, determined ultrasonically, were found to be sensitive to relaxation, crystallization and phase decomposition phenomena in rapidly solidified metallic glasses. Analytical ultrasonics enables determination of the activation energies and growth parameters of the reactions. Therefrom theoretical models can be constructed to explain the changes in mechanical and physical properties upon heat treatment of glassy alloys. The composition dependence of the elastic moduli in amorphous Cu-Zr alloys was found to be related to the glass transition temperature, and consequently to the glass forming ability of these alloys. Dynamic ultrasonic analysis was found to be feasible for on-line, real-time, monitoring of metallurgical processes.

Non-contacting ultrasonic techniques and applications

Non-contacting ultrasonic techniques and applications

Ultrasonic measurement of internal temperature distribution

Implementation of advanced materials processing strategies are presently hampered by a lack of adequate process-control sensors. For the processing of basic materials, such as steel and aluminium, an internal temperature-distribution sensor is needed. For these metals, the velocity of ultrasound is well known to be a strong function of temperature. We have therefore explored the feasibility of precisely measuring the velocity-temperature relation for a particular steel grade and using this to convert an ultrasonic-velocity distribution (tomogram) for a hot steel body to an internal temperature distribution. To overcome the usual need in conventional tomography for many thousands of path-integral measurements along intersecting ray paths, a priori heat-flow information has been incorporated into the reconstruction algorithms. As a result, for uniformly cooling bodies with the simple geometries usually encountered (e.g. circular, square or rectangular cross sections), the number of measurements can be reduced from many thousands to as few as three to five. Initial experiments on austenitic steel samples of cylindrical and square cross section by using non-contact ultrasonic techniques have shown that this approach yields acceptable temperature profiles at temperatures of up to 750 °C.

Noncontact Ultrasonic Characterization of Ceramics

A noncontact ultrasonic technique for the characterization of piezoelectric ceramics is described. The velocity of a laser‐generated surface‐acoustic‐wave pulse propagating at the surface of the ceramic material is measured by an optical probe. The laser beam has an annular section in order to produce a conveniently strong ultrasonic pulse without overheating the surface. Applications to the characterization of PZT samples are described.