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May 1978

Volume 63, Issue S1, pp. S1-S87

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back to top Session DD. Physical Acoustics V: Ultrasonics Fatigue and Propagation in Solids
Invited Papers
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Ultrasonic Fatigue of Commercial Alloys (A)

W. L. Morris and O. Buck

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S73-S73 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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A machine capable of fatigue testing high‐strength alloys at 20 kHz and for temperatures up to 900 °C is described. An electrostatic approach used to measure specimen vibration amplitudes at temperature is also discussed, as well as methods to calculate the applied stress. The machine has been used to study the processes of fatigue crack initiation and propagation at 20 kHz on several aluminum alloys, for comparison of fatigue behavior of the same alloys at 10 Hz. The modes of crack initiation at 20 kHz were the same as at 10 Hz for the materials studied. However, localized heating was observed, which is associated with microcrack propagation at 200 kHz. The crack growth rate, therefore, was regarded and the fatigue lifetimes were substantially increased over those at 10 Hz.
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Internal friction, modulus defect, and harmonic generation in high‐amplitude vibration (A)

D. N. Beshers

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S73-S73 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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At vibrational strain amplitudes in the range 10−4 to 10−3, many metals and alloys exhibit rapid increases in internal friction and modulus defect. For brass and iron these increases have been shown to coincide with the first appearance of slip bands on the external surface. Very strong harmonic generation sets in at the same time, with the second harmonic rising sharply above a square‐law extrapolation. We have made quantitative studies of the spectrum as a function of amplitude up to the fifth harmonic, although higher orders are quite visible. The variation is complex. Some progress has been made in duplicating these spectra using computer modeling with a Fourier analysis of dislocation velocity as a function of stress. By combining mechanical and microscopic data, deductions can be made about the dynamics of the sources, at least in some instances.
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The application of fatigue testing at ultrasonic frequencies to materials science and technology (A)

Brigitte Weiss and Roland Stickler

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S73-S73 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Efforts to develop the ultrasonic fatigue test method for routine application to fundamental fatigue studies as well as to the evaluation of fatigue properties of engineering materials have led to progress in the following areas:
(1) Development of suitable test equipment including advanced control and read‐out electronic; efficient system to stabilize specimen temperature; systems to measure vibratory energy and strains; environmental test chambers; set‐up for elevated temperature testing;
(2) Improvements in the basic understanding of the resonance system, including the vibratory behaviour of specimens with non‐uniform cross‐section, non‐uniform distribution of mechanical properties, and of specimens containing defects; considerations of the effects of exposure of the specimen to cyclic deformation in the elastic and plastic range.
(3) Accumulation of ultrasonic fatigue test data for a number of bcc and fcc metals and engineering alloys (e.g., C‐steels, stainless steels, Al‐alloys, Cu‐alloys, Mo‐base alloys) up to loading cycles exceeding 109, careful statistical analysis of the test results leading to well characterized S‐N curves.
(4) Investigation of the frequency effect by comparison with data of conventional fatigue tests and by studies of the mechanism operative during cyclic exposure at various frequencies.
(5) Development of test system to measure crack propagation rates at low stress amplitudes and to determine threshold‐stress values for crack growth under cyclic loading; this system appears as a time saving method for the determination of essential fracture mechanics properties.
Experimental results will be presented. Advantages and limitations of the ultrasonic fatigue test method will be discussed in detail.
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The use of high power ultrasonics (macrosonics) in studying internal friction and fatigue in metals (A)

Warren P. Mason

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S74-S74 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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High Power Ultrasonics has been a useful tool in studying fatigue and internal friction in metals since a large number of cycles can be obtained in a short time. It was first used by the speaker at Bell Laboratories in 1956. Further work was done at Columbia using an improved arrangement. Brass, copper, iron and titanium were studied. The first three fatigued plastically, whereas titanium fatigued elastically by slipless cracks. A correlation between internal friction and breakaway of dislocations and with two stages of plastic deformation has been found. Optical and electron microscope pictures show the various mechanisms up to the fatigue region. Electron microscope pictures show that fatigue cracks progress much faster for ultrasonic vibrations than for the slower fatigue tests. While the structure changes are somewhat different for ultrasonic vibrations than for low frequency testing, the number of cycles to fatigue is slightly larger for ultrasonic testing than for low frequency testing except for steel.
Contributed Papers
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Use of ultrasound in the prediction of fatigue life (A)

R. K. Lamerand and K. Salama

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S74-S74 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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The effects of strain range on the ultrasonic fatigue lifetime have been investigated in brass and aluminum. The fatigue of resonant dumbell specimens was carried out by means of a piezoelectrically driven exponential horn vibrating at a frequency of 20 kHz, and a displacement amplitude ranging between 10−4 and 10−6 meters. These specimens consisted of a gauge length with an arc of circular profile, flanked by a constant cross‐sectional area shoulder. The stress distribution along the gauge length was calculated by considering a hyperbolic cosine function to represent the arc of the circle. Four different sized specimens were used such that the calculated stresses predict their failure to occur over a range between 104 and 109 cycles. All the fatigue tests were performed at a controlled temperature of 0 °C. The results obtained experimentally showed that the number of cycles to failure reasonably agree with Manson's fatigue life predictions in the elastic strain range. This seems to indicate that low‐frequency fatigue life in brass and aluminum can be predicted from ultrasonic fatigue tests.
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Spectrum analysis of elastic wave scattering from cracks in metals (A)

Kent Lewis, Peter Szilas, Dale Fitting, and Laszlo Adler

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S74-S74 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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A broadband incident of longitudinal ultrasonic wave is scattered and mode converted at cracks (of different shapes and sizes) in diffusion bonded titanium. The scattered longitudinal and shear waves are analyzed by an analog spectrum analyzer. The RF signal is also digitized and Fourier analyzed. A geometrical theory of diffraction for elastic waves was developed which is based on (1) Keller's diffraction theory [J. Appl. Phys. 28, 426 (1957)] and (2) Maue' solution to the semi‐infinite plane for elastic waves [Z. fur Angew. Math. u. Mech. 33, 1 (1953)]. The experimentally observed spectra are compared to theoretical calculations. [This research was sponsored by the Center for Advanced NDE operated by the Science Center, Rockwell International, for the Advanced Research Projects Agency and the Air Force Materials Laboratory under Contract F33615‐74‐C‐5180.]
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Direct measurements of acoustic boundary waves (A)

R. O. Claus and C. H. Palmer

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S74-S74 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Direct optical measurements of Stoneley waves, acoustic boundary waves that propagate along the plane interface separating two solids having suitably related elastic constants, are reported [R. Stoneley, Proc. R. Soc. London A106, 416–428 (1924)]. To obtain these measurements, new solutions to Stoneley's equation suggesting wave propagation between several optically transparent media pairs were determined. Stoneley waves were generated using two acoustic wave conversion techniques on four of these pairs and detected using a modification of a differential interferometric optical technique initially developed for measurements of surface, shear, and dilitational waves [C. H. Palmer, J. Acoust. Soc. Am. 53, 948–949 (1973)]. Theoretical and experimental wavelengths agree to within two percent. Possible applications in seismological modeling and in the nondestructive evaluation of laminated structures and adhesive bonds are suggested.
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Measurements of the acoustic emission in a steam sodium interaction (A)

W. M. Carey and T. N. Claytor

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S74-S74 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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The acoustic emissions from the interaction of steam and sodium have been measured in the Argonne Core Components test loop for liquid sodium temperatures of 204 °C and 482 °C, liquid sodium flow rates of 0.23 m/s and 0.69 m/s and steam injection rates between 1.67 and 16.7 mg/s. These measurements were performed with a calibrated high temperature lithium niobate microphone which has a flatresponse to 25 kHz with a sensitivity 0.011 PC/Pa and rises at 12 dB per octave between 30 and 90 kHz to a peak of 0.062 PC/Pa. These data were observed to have low frequency (less than 10 kHz) and higher frequency (greater than 20 kHz) components. The lower frequency data was found to be consistent with hydrogen bubble formation and oscillation. The higher‐frequency component was observed to consist of transient events with center frequencies between 20 and 40 kHz. The amplitude of the individual events appeared independent of injection rate; however, the repetition of the transient events was found to be proportional to the steam injection rate to the 0.5 power. These high frequency transients were observed to be between 150 and 500 uμs in duration with peak pressure levels of 140 dB re 1 uμPa. Data at the lower frequencies was found to have some differences in the nature of the transients indicating a temperature dependence on the type of chemical reaction occurring.
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