Characteristics Of Ultrasonic Waves Research Articles

Time- and frequency-domain characteristics of laser-generated ultrasonic surface waves

The generation of elastic waves by illumination of a free metal surface with a laser pulse was studied to establish a quantitative basis for laser ultrasonics in nondestructive evaluation of surfaces. Experiments were carried out using a Q-switched Nd:YAG laser for generation and a wideband piezoelectric sensor for detection. A theoretical model for laser generation was developed for the thermoelastic energy regime. This model integrates over point source Green’s functions, suitably spread throughout the illuminated region. Good agreement was found between experiment and theory for characteristics in both time and frequency domains, for surface waves excited in the thermoelastic regime. For a given laser pulse energy, the highest Rayleigh wave peak frequency and bandwidth occurred when the Gaussian laser-beam half-width a was reduced just enough to begin surface damage. Once such damage commenced, further spot size reduction slightly lowered the peak frequency. Quantitative agreement with theory was found for the observed dependence, on both source–receiver distance and a, of the amplitudes for both the Rayleigh wave and the surface wave traveling at the bulk pressure wave speed (sP). In the nearfield, the sP wave overlapped the Rayleigh wave and made a greater contribution to the observed waveform than in the farfield.

Ultrasonic Spectroscopy for Teflon/Glass Bead Composite System

To investigate the frequency characteristics of ultrasonic waves transmitted through samples containing some foreign particles, ultrasonic Spectroscopy was carried out for Teflon/glass bead composite samples where bead sizes were varied from 850 µm to 25 µm. With the decrease of the bead size, the spectral amplitude first decreases over the whole frequency range, and the low frequency pattern recovers. The spectral amplitude takes minimum at a particular bead size depending on the frequency, and this minimum shifts to the small bead size side with the increase of frequency. Those behaviors are discussed with the theory of acoustic wave scattering.

弱い直交異方性体の音弾性関係の一般化

Since the anisotropy of ultrasonic SH wave velocities in plates was shown available to the nondestructive measurement of residual stress, much attention has been paid to the direction-dependence of propagation characteristics of ultrasonic waves. In this paper, it is intended to extend the acoustoelastic relation in slightly orthotropic materials to an arbitrary propagation direction of plane elastic waves. At first, the perturbation method was applied to the eigen value problem of the general acoustical tensor, and the formal solutions were obtained within the first-order of stress and the second-order of elastic anisotropy. Then these solutions were applied to the case where the effects of stress and anisotropy are of equal degree, and the velocities and polarization directions were explicitly expressed within the first-order of stress and anisotropy as the functions of the angles θ and φ specifying the propagation direction with respect to the principal axes of orthotropy. From these expressions, which are approximate but practically sufficient, the results previously obtained by Iwashimizu et al., King et al., and Thompson et al. were rederived by specializing the propagation direction. Finally, the simplification of the general relations was considered by imposing those restrictions on the anisotropic parameters, which are suggested by the theoretical analysis of macroscopic elastic constants of textured polycrystalline aggregates.

Ultrasonic wave attenuation spectra in steels

Recent work on well-characterised iron-carbon alloys has shown that the attenuation characteristics of high frequency ultrasonic waves depend on the mean grain size, the grain size distribution and on a damping term that has been associated with dislocations. Methods of analysis of the attenuation spectra are presented which offer the possibility of isolating each of these parameters so that their separate influence on mechanical properties can be investigated. Some typical results on particular alloys are presented to illustrate the analysis.

An Ultrasonic Device for Nondestructive Testing of Oilwell Cements at Elevated Temperatures and Pressures

Summary This paper describes a measuring technique and a hardware system that automatically monitors and records the complete history of compressive strength development and initial set of oilwell cement slurries under high pressures and high temperatures (HP/HT). The design is based on the transmission characteristics of ultrasonic compressional waves through cement slurries. In principle, an analyzer measures the transit time (reciprocal of velocity) of an ultrasonic wave pulse through a slurry sample, converts it to apparent compressive strength, and records the results continuously. One of the main advantages is that testing is nondestructive, and only one sample of slurry is required to determine both the compressive-strength development history and initial set of the cement slurry. Another important advantage of this device is that initial set of a cement slurry can be determined above 100 deg. C and at pressures far above atmospheric, the limiting factors in other methodsCompressive strengths, determined from ultrasonic transit time data, have shown deviations equal to or better than those obtained from mechanical tests. Since specimens are not removed and exposed to atmospheric pressure, the results should be more representative of actual downhole conditions. Also, the process promises to be well-suited to strength retrogression studies since there are no time gaps in the test results. Further experimental and analytical work is being carried out to evaluate the potential of this technique for measuring other slurry properties. Introduction The times required for and oil- or gaswell cementing slurry to reach an initial set and to develop useful compressive strength are important parameters in scheduling drilling or completion operations, such as temperature logs to locate top of cement fill, bond logs to evaluate cement jobs, continuation of drilling after setting intermediate casing or liners, perforating production zones, and cleanout and stimulation treatments. Without reliable set-time and compressive-strength data, temperature and cement bond logs can be run too soon or can be delayed unnecessarily. Further drilling also can be caned out either prematurely or later than needed, which translates into lost time and money. If cleanup and stimulation treatments are carried out too soon, inter-zone communication problems may develop. A complete knowledge of the history of compressive-strength development allows determination of the optimal time for perforation. This minimizes shattering and results in better zone isolation. Thus, a precise knowledge of initial set time and strength-development data is essential to perform these operations at the optimal time to avoid unnecessary delays. In the past, the usual method of determining the time required to reach initial set or a specific compressive strength was to cure a number of cube specimens in different HP/HT autoclaves and schedule test times that bracketed the strength value specified. Such procedures often wasted time and equipment. Problems were compounded in situations where slurries had to be specially tailored for a specific job. This is especially true for deep wells, where basic variations in the cement itself often necessitated extensive testing. JPT P. 2611^

Anomalous Attenuation of Piezoelectrically Active Ultrasonic Waves in Photoexcited Cadmium Sulfide

The structure-sensitive anomaly in the attenuation characteristics of ultrasonic waves in photoconducting single crystals of CdS illuminated with monochromatic light, reported earlier, has been further investigated. The attenuation and amplification characteristics, corresponding to various wavelengths of illumination, have been measured at room temperature and reduced temperatures in a number of samples, and in the same sample submitted to heat treatments in different ambients. The results obtained cannot be explained satisfactorily on the basis of existing theories, and the operation of an additional photosensitive loss mechanism, involving the piezoelectric field which accompanies the ultrasonic wave, has to be invoked. The possibility is examined that this extraneous attenuation arises as a result of photodielectric losses incurred by the piezoelectric field.

Structure-Sensitive Dependence of the Attenuation Characteristics of Ultrasonic Waves in Photoconducting Cadmium Sulphide on the Wavelength of Illumination

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