Nonlinear resonant ultrasound spectroscopy (NRUS) is a method that can be used for detecting microcracks in structures. NRUS detects shifts in resonance frequencies versus excitation amplitude. Excitation of the sample is typically done with a piezoelectric transducer. We have been applying an electromagnetic excitation developed for resonant ultrasound spectroscopy [S. Garrett, J. Acoust. Soc. Am. 88(1), 210–221 (1990)] as an alternative for NRUS excitation. It involves gluing a coil of wire onto the end of a rod-shaped sample and placing it in a magnetic field. By controlling which part of the coil is in the strongest part of the magnetic field, we can control the principle direction of the driven oscillations in the rod. This method allows us to selectively excite longitudinal, torsional, and bending vibrations and measure the nonlinear properties of the sample for each type of vibration. We have applied this electromagnetic method to measuring the nonlinear properties of Berea sandstone, and we plan to use it to detect stress corrosion cracking in stainless steel samples. The purpose of this presentation is to illustrate the usefulness of the electromagnetic method.
Moving-coil loudspeaker parameters are typically derived from electrical impedance measurements. Leishman and Anderson previously provided the theoretical foundations for extracting these parameters from sound transmission measurements conducted in a plane wave tube. This presentation will discuss experimental results of using this idea to extract the parameters of moving-coil drivers and those of passive radiators, the latter of which cannot be derived from electrical impedance measurements. The two-load method is used to account for the non-anechoic behavior of the tube to better enable accurate extraction of the sound transmission. Mechanical parameters are extracted from an open-circuit sound transmission measurement, and the electrical parameters are extracted by placing a wire across the loudspeaker’s terminals to provide a closed-circuit sound transmission measurement. Parameters extracted from measurements of electrical impedance, sound transmission, and destructive analysis of diaphragm assemblies will be compared.
Spent nuclear fuel is often stored in stainless steel canisters in the United States. Stainless steel is susceptible to Stress Corrosion Cracking (SCC). This presentation will discuss progress on the use of the Time Reversed Elastic Nonlinearity Diagnostic (TREND) and Nonlinear Resonant Ultrasound Spectroscopy (NRUS) to determine whether SCC is present and attempt to quantify the depth of the cracking. NRUS is the measurement of the amplitude dependence of a sample’s resonance frequency, which occurs because of a softening of the elastic modulus in damaged media. NRUS provides a global indication of damage in a sample. TREND employs time reversal acoustics, which focuses wave energy at various points of interest to excite localized high amplitude. The amplitude dependence of this localized energy allows pointwise inspection of a sample. [This work was funded by the Nuclear Energy University Program of the U.S. Department of Energy through a subcontract from Los Alamos National Laboratory.]
Nonlinear resonant ultrasound spectroscopy (NRUS) is a method that can be used for detecting microcracks in structures. NRUS detects shifts in resonance frequencies versus excitation amplitude. Excitation of a sample is typically done with a piezoelectric transducer. Here, the application of an electromagnetic excitation is explored as an alternative for NRUS excitation. It involves gluing a coil of wire onto the end of a rod sample and placing it in a magnetic field. By controlling which part of the coil is in the strongest part of the magnetic field, the principle direction of the driven oscillations in the rod can be controlled. This method allows selective excitation of longitudinal, torsional, and bending vibrations, and the measurement of the nonlinear properties of the sample for each type of vibration is therefore possible. Both a piezoelectric transducer and electromagnetic excitation are used to measure the nonlinear elastic parameters of a Berea sandstone rod. The effects of heating of the sample and slow dynamics are explored and compared with each type of excitation. The purpose of this presentation is to illustrate the usefulness of the electromagnetic method and outline its differences from the piezoelectric method.
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