Resonant Ultrasound Spectroscopy Method Research Articles

Elastic constant measurements at elevated temperatures.

Resonant ultrasound spectroscopy (RUS) is a technique in obtaining the full elastic tensor of single crystal materials by measuring the mechanical resonances of a polished sample. Elastic constants of materials are a sensitive probe into the atomic environment; therefore, they are useful tools for studying phase transitions at high temperatures. A high-temperature system in which test samples are in direct contact with two transducers was designed to conduct RUS measurements up to 650 °C. Extremely high-temperature (∼650 °C) measurements are made possible by separating the sample, placed in a tube furnace, and the transducers with buffer rods made of low-acoustic attenuation materials with good thermal stability such as ceramic alumina or fused quartz. Results from the high-temperature measurements on a standard thermoelectric material, silicon-germanium, demonstrated that the system has the ability of acquiring resonance signals at temperatures up to 1000 °C. Experimental issues such as additional resonance peaks introduced by the buffer rods and sample loading will be addressed. The apparatus has been used to study phase transitions in transition metal oxides and novel Zintl phase thermoelectric materials. These results demonstrate the great potential of RUS methods in high-temperature physics.

Ultrasound-Induced Structural Anomaly of Supercooled Liquid in Some Bulk Metallic Glasses

We have studied the elastic and anelastic behavior of fully structural-relaxed Pd40Ni40P20 and Zr55Al10Ni5Cu30 bulk metallic glasses using high-frequency ultrasound vibrations at elevated temperature, and found that the structural anomaly is induced by ultrasound vibrations in a supercooled liquid region. The electromagnetic acoustic resonance and resonant ultrasound spectroscopy methods were employed to measure the resonant spectra and ultrasonic attenuation coefficients. When the glassy samples are subjected to sub/low-MHz ultrasound vibrations during heating process, the crystallization is accelerated around their glass transition temperatures, and with this abrupt structural change, irregular � shaped internal friction peaks appear. From the standpoint of ultrasonic echography, the glass transition and crystallization temperatures are considerably lowered by ultrasound vibrations in the present measurements.

Elastic properties of hot-isostatically-pressed magnesium diboride

Magnesium diboride was hot-isostatically pressed using three qualitatively different cycles: dense material cooled under pressure (DMCUP), “standard” cycle with pressure and temperature simultaneously reduced, and isothermal pressure release. Elastic properties of dense MgB2 were measured at normal conditions using resonant ultrasound spectroscopy method. The highest values of elastic moduli correspond to the sample processed using DMCUP cycle. The data for fully dense samples are in satisfactory agreement with theoretical predictions based on quantum mechanics calculations. The effect of lower density on elastic constants is consistent with a theoretical approach based on elasticity theory taking into account effect of porosity.

Resonant ultrasound spectroscopy in shear mode

We present an enhancement of the resonant ultrasound spectroscopy method for the determination of elastic and viscoelastic properties. By using shear transducers rather than the usual compressional ones, signal strength for the fundamental is enhanced by one to three orders of magnitude. This enables simplified determination of shear modulus and damping tan δ with off-the-shelf electronics. Moreover, the polarization of the shear transducers can be used to identify modes of vibration.

Complete mode identification for resonance ultrasound spectroscopy

This study is devoted to deducing exact elastic constants of an anisotropic solid material without using any advance information on the elastic constants by incorporating a displacement-distribution measurement into resonant ultrasound spectroscopy (RUS). The usual RUS method measures free-vibration resonance frequencies of a solid and compares them with calculations to find the most suitable set of elastic constants by an inverse calculation. This comparison requires mode identification for the measured resonance frequencies, which has been difficult and never been free from ambiguity. This study then adopts a laser-Doppler interferometer to measure the displacement-distribution patterns on a surface of the vibrating specimen mounted on pinducers; comparison of the measured displacement distributions with those computed permits us to correctly identify the measured resonance frequencies, leading to unmistakable determination of elastic constants. Because the displacement patterns are hardly affected by the elastic constants, an exact answer is surely obtained even when unreasonable elastic constants are used as initial guesses at the beginning of the inverse calculation. The usefulness of the present technique is demonstrated with an aluminum alloy and a langasite crystal.

Elastic property of aged duplex stainless steel

We have measured the elastic constants of duplex stainless steel, JIS-SCS14A (CF8M), aged isothermally at 400 °C up to 10,000 h, using resonant ultrasound spectroscopy method. The elastic constant c 11 (= λ+2 μ) increases monotonically with the aging time, but c 44 (= μ) remains virtually unchanged. Using a micromechanics model, we have deduced the elastic constants of α-phase on the assumption that those of γ-phase are unchanged with the aging. The increase of the α-phase elastic constants reflects the spinodal decomposition of α-phase.

Contactless mode-selective resonance ultrasound spectroscopy: Electromagnetic acoustic resonance

A noncontacting resonant-ultrasound-spectroscopy (RUS) method for measuring elastic constants and internal friction of conducting materials is described, and applied to monocrystalline copper. This method is called electromagnetic acoustic resonance (EMAR). Contactless acoustic coupling is achieved by energy transduction between the electromagnetic field and the ultrasonic vibrations. A solenoidal coil and static magnetic field induce Lorentz forces on specimen surfaces without using a coupling agent. By changing the field direction, a particular set of vibration modes can be selectively excited and detected, an advantage in identifying the vibration modes of the observed resonance peaks. Contactless coupling allows the measure of intrinsic internal friction free from energy loss associated with contact coupling. The elastic constants and internal friction measured by EMAR are compared with those by the usual RUS method for a rectangular-parallelepiped copper monocrystal. Both methods yielded the same elastic constants despite fewer resonant peaks in the EMAR case. The two methods gave essentially the same shear-mode internal friction, but the RUS method gave higher volume-mode internal friction.

Ultrasonic Characterization of Inertial Confinement Fusion Targets

Inertial confinement fusion (ICF) targets designed to achieve ignition must meet strict surface smoothness and sphericity requirements. One potentially valuable method for evaluating the quality of these targets is resonant ultrasound spectroscopy (RUS). When applied to simple geometries, such as layered spheres or rectangular parallelepipeds, RUS may yield significant information about alloy homogeneity, elastic constants, cavity geometry, the presence of gross defects such as cracking or hemishell bonding problems, and properties of interior fluids. The strengths of RUS techniques for ICF target characterization include applicability at all temperatures of interest with a single apparatus, high sensitivity in frequency spectral measurements, and the inherent acoustic indifference to optically opaque samples. Possible applications and the limitations of RUS methods for examining layer geometry and material properties are addressed. Preliminary room temperature experiments with a deuterium-filled aluminum shell are used to evaluate the utility of many of the described applications. The frequency spectrum compares favorably with theory and displays measurable mode splitting, acoustic-mode resonance widths indicative of cavity boundary dissipative mechanisms, and low-Q elastic modes. The acoustic cavity resonance structure confirms the internal gas density and is used to calculate the two lowest even-order cavity boundary perturbation amplitudes.