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Nov 1982

Volume 72, Issue S1, pp. S1-S108

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back to top Session H. Shock and Vibration I: Fatigue in Structures
Invited Papers
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Nondestructive detection of fatigue damage (A)

Robert E. Green, Jr.

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S14-S14 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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This paper will discuss the various nondestructive techniques which have been used or which are potentially useful for detection of fatigue damage. The ideal nondestructive testing technique would permit very early detection of fatigue damage so that proper assessment of the severity and rate of severity increase of the structural damage leading to failure can be made. Thus, the most sensitive systems would be capable of detecting motion, pileup, and breakaway of dislocations; the next most sensitive systems would be capable of detecting microcracks; the least sensitive systems would only be capable of detecting macrocracks. It is practically expedient to have nondestructive techniques which can successfully detect fatigue damage in each of these regimes since some components can tolerate larger amounts of fatigue damage or larger crack sizes than others without serious concern for the structural integrity of the component. It will be shown that the best nondestructive technique for detecting and sizing of macrocracks is ultrasonics; the best nondestructive techniques for detection of microcrack formation and possible pre‐microcrack fatigue damage are ultrasonic attenuation and acoustic emission; a large number of nondestructive techniques for residual stress (strain) measurements are candidates for extremely early fatigue damage detection, with current interest primarily directed at ultrasonic wave velocity measurements.
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Ultrasonic characterization of fatigue in advanced composite materials (A)

John H. Cantrell, Jr.

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S14-S14 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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In contrast to fatigue of metals which tends to originate from crack initiation at identifiable defect sites, fatigue of fiber‐reinforced composite materials has not been identified with a single dominant failure process. Rather, fatigue of such materials is manifested by several damage mechanisms including through‐the‐ply cracks, fiber disbonds, and delaminations. The presence of multiple damage mechanisms presents special problems both in understanding the fundamental nature of failure in fiber/matrix composites as well as in their nondestructive evaluation. Ultrasonic methods for characterizing fatigue damage in fiber/matrix composites will be examined with special emphasis on quantitative measurements of attenuation, velocity, and the values of the linear and quadratic attenuation coefficients measured as a function of frequency. The effect of ultrasonic phase cancellation errors due to material anisotropy and inhomogeneity as well as the influence of pulse shape artifacts on quantitative measurements are discussed.
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Ultrasonic studies of mechanical properties of materials (A)

A. V. Granato

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S14-S14 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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In recent studies, the close relationship between ultrasonic attenuation and the plastic flow of solids has become more explicit. Both depend sensitively upon the details of dislocation‐defect interactions. The interactions can be separated into those producing pinning and those producing viscous drag. Deformation behavior can be classified according to the strength of the drag. For small drag, as in superconductors, inertial effects become important. For intermediate drag, traditional theories resting on rate theory treatments become applicable. For large drag, viscoelastic behavior is obtained. Measurements are examined for information concerning the basic nature of different sources of short‐ and long‐range pinning and of drag.
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Interaction of ultrasonic waves with cracks (A)

Laszlo Adler

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S14-S15 (1982); (2 pages)

Online Publication Date: 12 Aug 2005

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An overview is presented on recent studies of ultrasonic waves interacting with artificial and real cracks. Various experimental methods will be described to obtain quantitative information concerning both geometrical [such as size, orientation] parameters as well as physical and surface parameters [such as stress intensity, surface roughness, distribution function, closure] of cracks. Various analytical approaches to support experimental results and carry out inversions will also be emphasized. [Work supported by DARPA/AF through Ames Laboratory.]
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Application of x‐ray diffraction to monitor fatigue deformation in high strength alloys (A)

Robert N. Pangborn

J. Acoust. Soc. Am. Volume 72, Issue S1, pp. S15-S15 (1982); (1 page)

Online Publication Date: 12 Aug 2005

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A number of x‐ray diffraction techniques have been applied to measure the fatigue deformation introduced during axial and flexural loading in high strength aluminum and nickel base alloys. X‐ray double‐crystal diffractometry and x‐ray line‐broadening analyses were conducted to evaluate the localized and average microplasticity, respectively, generated prior to crack initiation. The modifications in diffraction peak profiles recorded using these techniques were interpreted in terms of changes in lattice distortion and dislocation density and correlated to the surface topographic features developed during fatigue cycling. These methods were also utilized to examine the fatigue deformations accrued in the subsurface and bulk of the samples. Both stepwise removal of surface layers and nondestructive evaluation using x rays of different penetration capability were employed to obtain the depth profiles. X‐ray stress measurements were made to disclose the modifications in residual stress occurring during fatigue, their relationship to the dislocation distribution, and their role in crack nucleation. The combination of x‐ray methods provided information useful both to identification of the failure mechanism and to monitoring cumulative deformation preceding ultimate failure, even under spectrum amplitude testing conditions.
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