K.J. Sun

Propagation of Acoustic Waves in a Copper Wire Embedded in a Curing Epoxy

This paper investigates the propagation o f 0.8 to 5.8 MHz acoustic waves in a copper wire embedded in a curing epoxy. The acoustic amplitudes were measured as a function of time and temperature at atmospheric pressure. It was observed that the acoustic amplitude was sensitive to the epoxy state and temperature. For the initial portion of the cure cycle, the attenuation of all the acoustic modes excited in the wire increased. As the cure p rogressed, the attenuation of one mode began to decrease. The velocity of this mode was slightly less than the shear velocity of copper. The frequency of this mode is shown to be dependent on the ratio of the acoustic wavelength to the diameter of the wire. An independent measure of the shear velocity of epoxy indicates a functional dependence between it and the attenuation of the mode, which indicates the potential for measuring the acoustic p roperties of curing resins under extreme conditions such as high temperature or pressure with copper wires.

Effect of Rivet Rows on Propagation of Lamb Waves in Mechanically Fastened Two-Layer Aluminum Plates

Feasibility of using Lamb waves for disbonds and corrosion detections in aircraft fuselage structures was investigated in recent years. Measurement performed on various laboratory-fabricated specimens as well as on panels removed from aircrafts has shown consistent results and demonstrated its potential applications for large area structural integrity evaluation [1–3]. It has been observed that structural flaws existing on the path of Lamb waves not only changed amplitude of waves but also affected their velocities as well. Amplitude change caused by a disbond of size less than 0.5 in. × 0.5 in. was significant and has been measured. Variation in phase velocity was used to quantify the corrosion-induced thickness reduction in aluminum sheets. An area of size 1 in. × 1 in. with 8% thickness loss in subsurface of an 1 mm thick aluminum plate was detected by monitoring the phase velocity increase of SO mode. While these tests made major progresses toward developing a practical and low cost flaw assessment system, effects due to the presence of certain structural elements, such as coatings and fasteners, on the propagation of Lamb waves are becoming important issues, and need to be analyzed. These effects are themselves interesting physical phenomenon and worth investigation, however, it is hoped that propagation variations of waves induced by structural defects can be separated from these effects and be quantitatively correlated to the physical properties of defects.

Mode conversions of Lamb waves for inspection of disbonds

Disbond detection with Lamb waves is tested on lap splice joints and on laboratory specimens consisting of bonded aluminium sheets. Significant amplitude variation is observed between propagation over bond and disbond. Measurements conducted on laboratory specimens with different geometry of disbonds and on aircraft skins show results consistent with those obtained by standard C-scan ultrasonic test and other techniques.<<ETX>>

Relaxation behavior of ultrasonic attenuation in YBa/sub 2/Cu/sub 3/O/sub 7/

It is shown that temperature-dependence ultrasonic attenuation data of YBa/sub 2/Cu/sub 3/O/sub 7/ at various frequencies exhibit anomalies at temperatures close to T/sub c/. These attenuation maxima are found to be the result of a relaxation mechanism added on top of an unusual attenuation background. It is proposed that the grain boundary motions induced by the structural distortion and the propagation of sound waves enhances the energy dissipation around T/sub c/. Whether this structural distortion is the consequence of the onset of a superconducting state remains undetermined. It is also possible that either a tunneling effect of the acoustoelectric effect contributes to sound energy dissipation. The temperature dependence of ultrasonic velocity shows a softening around T/sub c/ which may be an intrinsic property of high-temperature superconductors. >

Ultrasonic absorption in the magnetic superconducting system Er1−x\HoxRh4B4

Ultrasonic attenuation measurements as a function of temperature at constant magnetic fields and as a function of magnetic field at constant temperatures in Er1−xHoxRh4B4 show interesting behavior at low temperatures. The enhanced attenuation observed in the superconducting state and the sharp change in attenuation at magnetic phase transition for the superconductors in this system are attributed to spin‐phonon interaction. The peculiar dependence of attenuation on orientation of magnetic field with respect to sound wave propagation direction evidences indirectly the coexistence of magnetic order and superconductivity. A two‐level model of phonon‐phonon interaction is proposed to elucidate the occurrence of relaxation type attenuation maxima observed in the temperature‐dependent attenuation curves of all the samples. Furthermore, the attenuation behavior at low temperatures in high magnetic fields may also manifest the occurrence of a new magnetoelastic coupling effect.

Ultrasonic Attenuation Measurement in High T C Superconductors and Heavy Fermion Superconductors

We have measured the ultrasonic attenuation in the heavy fermion superconductors UPt3 and URu2Si2; and also in pressed pellets of the high T superconductors, RBa Cu 0 with R = Y, Lu and Ho. departures from the behavior in conventional superconductors; both in the temperature and field variations. In magnetic field measurements a sharp peak is seen in the attenuation; separating two regions which may be two distinct superconducting phases. In the high Tc samples a large velocity change is seen. In one of the single phased sample, YBa2Cu307, a large attenuation maximum is seen below T. 2 37 In UPt3 the attenuation shows marked

Relaxation Attenuation in Er 0.187 Ho 0.813 Rh 4 B 4 and HoRh 4 B 4

The temperature dependence of the ultrasonic Rh B and attenuation of samples of Er HoRh B was measured at diffg+ii

Ultrasonic-attenuation measurements in single-phased YBa/sub 2/Cu/sub 3/O/sub 7/

frequencles. A bell-shaped maximum observed in each of the attenuation curves shifted to higher temperatures when the impressed frequency was increased. The maximum is believed to be a relaxation type attenuation maximum which is associated with the splitting of the ground state of the Ho3+ ions. An expression which relates the attenuati n to the oscillation of the energy levels of the €iog+ ions due to the propagation of an ultrasonic wave through the sample is derived. qualitatively agree with this Debye equation. The temperature dependence of the relaxation time between the energy levels may be obtained from the experimental results by using this equation, and yields reasonable shifts in temperature for the attenuation maxima at different frequencies. H00.813 4 4 4 4 The experimental results