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Nov 1981

Volume 70, Issue S1, pp. S1-S109

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back to top Session Z. Physical Acoustics IV: Ultrasonic Characterization of Materials. II
Contributed Papers
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Industrial ultrasonic tomography (A)

M. C. Tsao

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S56-S56 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Based on applications, ultrasonic tomography can be classified into two categories, reflective tomography and transmissive tomography. Reflective tomography offers the most potential for characterizing the shapes and sizes of cracks, voids, inclusions, corrosion, erosion, detachment of bonds, or imperfections in weldments. The underlying principle of reflective tomography is to use the Time‐of‐Flight information from sound pulses to determine the location of discontinuities in an otherwise homogeneous material. Transmissive tomography, on the other hand, is most effectively used for determining more general variations in density. In this case, both Time‐of‐Flight information and variations in sound level attenuation are used to characterize the material properties of concern. Although the end results of displaying the reconstructed images are essentially the same for the two cases, the logic and algorithms are considerably different. The systems and examples of applications of both methods are discussed.
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Elastic wave propagation in materials with columnar grain structure (A)

Dale Fitting, Laszlo Adler, Ben Oliver, and Bruce Dewey

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S56-S56 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Several important structural materials (i.e., austentic stainless‐steel welds and centrifugally‐cast piping) are strongly anisotropic as a result of a columnar grain structure. Progress in modelling ultrasonic wave propagation in such materials is presented. Because elastic wave propagation in polycrystalline metal having a columnar grain structure is so complex, initial studies were directed toward components of these structures. Large single crystals of nickel were grown and the coordinate axes determined by x‐ray diffraction. The elastic constants for the crystalline samples were measured using an ultrasonic pulse‐transit‐time technique. Specimen properties were input to a finite‐element model of wave propagation. Results for elastic wave interactions at sample boundaries are given. [This work is supported by Basic Energy Science Program D.O.E.]
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Frequency dependence of ultrasonic waves scattered from surface breaking cracks (A)

Dale Fitting, Michel de Billy, and Laszlo Adler

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S56-S56 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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An ultrasonic spectroscopy system is used to study frequency dependence of scattered ultrasonic waves from surface breaking cracks in metals. Crack parameters such as depth, length, and surface conditions are correlated to the frequency dependence of the scattered amplitude. Both bulk and surface waves have been used. Experimental results have been compared to existing theories. [This work is supported by ARPA/AFML. Program on QNDE through Ames Laboratory.]
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Spectral discontinuities of diffracted waves by periodic corrugated surfaces (A)

Alain Jungman, Laszlo Adler, and Gerald Quentin

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S56-S56 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Anomalies in the spectrum of elastic wave scattering from periodically corrugated structures have been reported (100th ASA Meeting). They are interpreted as mode converted signals along the interface. Measurements are now carried out showing that these sharp minima are not only observed in the normally incident backscattered situation. Spectral discontinuities are also observed under specular non normal reflection from liquid‐solid and solid‐air periodic interfaces. In addition, the frequency dependence of the minima has been measured as a function of the orientation of the plane of incidence versus the lines of the gratings. Some attempts are made to fit available theories of diffraction with present boundary conditions. The position and the amplitude measurements of the discontinuities can be used to approach some geometrical and physical properties of the interface.
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Rayleigh wave spectroscopy for measuring the depth of shallow open fatigue cracks (A)

C. P. Burger and A. J. Testa

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S56-S56 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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The energy in a Rayleigh surface wave is essentially contained in a surface layer less than two wavelengths deep. A broadband pulse will, therefore, have all its high‐frequency components close to the surface with only the low frequencies penetrating to the deeper layers. This property of a Rayleigh wave, whereby the frequency spectrum of a pulse varies with depth below the surface, is used to find the depth of open surface breaking fatigue cracks with depths less than the lowest frequency component of the incident wave. The technique is not affected by the path of the crack, its inclination, branching roughness or the presence of residual stresses. It, therefore, measures accurately that property of surface cracks which arc most significant with respect to fracture, life prediction and safety assurance. The paper describes the technique and shows how automatic on‐line pattern recognition procedures can be used to measure the depth to a resolution of 0.2 mm. Examples are given for the profiling of a rough surfaced crack.
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Scattering of an elastic wave by a surface‐breaking crack (A)

Daniel A. Mendelsohn, Jan D. Achenbach, and Leon M. Keer

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S56-S57 (1981); (2 pages)

Online Publication Date: 12 Aug 2005

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Scattering of incident surface waves and incident body waves by a surface‐breaking crack in a homogeneous isotropic elastic solid is investigated in a two‐dimensional geometry. By decomposing the scattered fields into symmetric and antisymmetric fields with respect to the plane of the crack, two boundary value problems for a quarter‐plane have been obtained. The formulation of each boundary‐value problem has been reduced to a singular integral equation which has been solved numerically. For incident surface waves the exact backscattered and forwardscattered surface waves have been plotted versus the dimensionless frequency. An asymptotic approximation to these surface motions for high frequency is also presented as a function of dimensionless frequency. Curves are also presented for the exact scattered displacement fields in the interior of the body generated by incident body waves, both versus the angle of incidence and versus the dimensionless frequency.
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Scattering of elastic waves from double defects in solids (A)

B. R. Tittmann, F. Cohen‐Tenoudji, L. Ahlberg, and G. Quentin

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S57-S57 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Scattering of longitudinal waves from double defects embedded in Ti alloy is discussed in terms of comparisons between experimental and theoretical results. Results are presented for two overlapping cavities, two adjacent cavities, a cavity with a circular crack, and an inclusion with a crack at one side. The data are discussed for both the time and frequency domains. An effort is made to identify significant features by ray tracing arguments. The results cover the range of ka from 0.g to 4, where k is the ultrasonic wave factor and a is the radius of the main defect. [This work was in part supported by the Center for Advanced NDE operated by the Ames Laboratory USDOE, for DARPA and AFWAL/AFML under Contract No. W‐7405‐Eng‐82.]
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Limitations on the use of short‐pulse ultrasonic transducers for characterisation of small targets in solids (A)

J. P. Weight and A. F. Brown

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S57-S57 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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A convenient model explains the field pattern of a short‐pulse broadband ultrasonic transducer in terms of a plane wave propagating in the geometrical region straight ahead of the face, together with a diffracted edge wave. That these waves actually exist is demonstrated by visualization and field‐probing techniques. Interaction of plane and edge waves produces field patterns which, for the special case of continuous waves, lead to the definition of the nearfield and farfield regions. This paper extends the results of Weight and Hayman [J. Acoust. Soc. Am. 63, 396–404 (1978)] to solids. A simple model is proposed to take account of mode conversion of short pulses and hence to explain the added complexities of the echo system which arise from the use of these pulses to improve resolution. The consequences for materials evaluation are discussed.
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Thermal wave microscopy of doped silicon crystals (A)

R. C. Farrow, M. K. Thomas, and D. C. Joy

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S57-S57 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Thermal wave microscopy in the scanning electron microscope offers profiling studies of semiconductors that is inexpensive and nondestructive. The technique monitors the sound induced by the thermoelastic effect of a pulsed electron beam in solid samples. Sound is detected by a piezoelectric transducer on which the sample is mounted. The thermal wave signal is critically damped and extends only one wave length below the surface. Variations in the thermal properties of the material within the range will change the amplitude and phase of the thermal wave and hence of the ultrasonic signal that this produces. A depth profile can therefore be deduced by such measurements. In this paper, preliminary results of a study of doped silicon samples are presented. Differences in sound amplitude between doped and undoped regions are related to thermal conductivity differences. The amplitude difference as a function of phase and frequency will also be discussed with the aim of clarifying the nature of the depth sensitivity of the technique by a comparison with existing theories.
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Velocity and attenuation in saturated glass beads (A)

T. J. Plona and David Linton Johnson

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S57-S57 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Based on the Biot theory for propagation of sound in a fluid‐saturated porous medium, the velocity and attenuation of compressional waves has been studied as a function of frequency in water‐saturated unconsolidated glass beads. We have made ultrasonic measurements in the 200 kHz to 5 MHz range on a collection of samples of mono‐sized spheres with mean particle size ranging from 20–500 μm. The measured attenuation is shown to be in agreement with theory both in magnitude and in frequency dependence in the high‐frequency limit where an ∫1/2 behavior is predicted. in this range, the loss increases as permeability decreases. For the smallest size particles, the low‐frequency transition to an ∫2 behavior in the attenuation is also observed as well as the predicted velocity dispersion. For all the samples, high enough frequencies were used in the measurements such that scattering effects were observed. Thus, the transition from nonscattering (Biot) losses to scattering losses will also be discussed. An interpretation of the scattering loss in terms of multiple scattering has been discussed elsewhere [H. Levine et al., Proc. Seventh Annual Midwestern Mechanics Conference (1981)].
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An ultrasonic light diffraction technique for studying acoustic wave propagation in air above 1 MHz (A)

Ward A. Riley, L. Alan Love, and David W. Griffith

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S57-S57 (1981); (1 page)

Online Publication Date: 12 Aug 2005

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Studies of ultrasonic light diffraction above 1 MHz in bulk media have normally been conducted in liquids and solids due to the difficulty of generating and propagating ultrasonic waves in gases. A sensitive broadband optical diffraction technique has been used to study the propagation of ultrasonic waves in air in the low megahertz frequency range. An ultrasonic beam at 1.4 MHz was produced in air by driving a medical ultrasound transducer (circular face, unfocused, 13‐mm diameter) with a narrowband rf pulse having a peak potential amplitude of 300 V. The radiated waveform and power of approximately 30 mW was detected with a 1‐mm‐diam laser beam from approximately 2–30 mm from the transducer face. The fundamental frequency was found to experience an attenuation of −4.1 dB/cm over this range. A significant amount of the second harmonic was observed to be generated over this path length demonstrating the presence of nonlinear acoustical phenomena. This technique could be useful for studying the fundamental propagation characteristics of ultrasound in gases above 1 MHz and for the analysis of broadband acoustic pulses having significant frequency content above 200 kHz. In practical application, it should be possible to place an upper limit on the acoustic power levels radiated into air by medical diagnostic pulse‐echo systems with this approach. [Work supported by NIGMS 27755.]
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Some parameters affecting backscattering reflection of ultrasonic waves at the Rayleigh angle for a liquid‐solid interface (A)

M. de Billy, L. Adler, and G. Quentin

J. Acoust. Soc. Am. Volume 70, Issue S1, pp. S58-S58 (1981); (1 page) | Cited 1 time

Online Publication Date: 12 Aug 2005

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It has been reported before that an ultrasonic beam incident at the Rayleigh angle to a liquid‐solid interface will produce a backscattered wave [S. Sasaki, Jap. J. Appl. Phys. 2, 198 (1963); W. G. Neubauer, J. Acoust. Soc. Am. Suppl. 1 68, S63 (1980); M. de Billy, these de doctorat d'etat (1980)]. Experimental results will be presented for various metals and glass. It appears that the backscattering is not due to grain structure or surface roughness alone but it is a finite beam phenomena. Results will be given for the effect of the beamwidth. This backscattering phenomena can be applied to measure the surface wave velocity for anisotropic materials.
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