1983 | OriginalPaper | Buchkapitel
Effects of Crack Closure on Ultrasonic Transmission
verfasst von : R. B. Thompson, B. J. Skillings, L. W. Zachary, L. W. Schmerr, O. Buck
Erschienen in: Review of Progress in Quantitative Nondestructive Evaluation
Verlag: Springer US
Enthalten in: Professional Book Archive
Aktivieren Sie unsere intelligente Suche, um passende Fachinhalte oder Patente zu finden.
Wählen Sie Textabschnitte aus um mit Künstlicher Intelligenz passenden Patente zu finden. powered by
Markieren Sie Textabschnitte, um KI-gestützt weitere passende Inhalte zu finden. powered by
Ultrasonic waves are attenuated as they propagate past the tip of a crack due to the reflection of the energy at the crack face and diffraction at the crack tip. Crack closure modifies the situation since partial transmission can occur at points along the crack face where asperities come in contact. This phenomenon is important in defining the ability to nondestructively detect closed cracks and in developing a more detailed understanding of the closure phenomenon itself. Modified compact tension specimens were used to investigate the effects of partial crack closure on focussed, through-transmission ultrasonic signals. Data obtained from fatigue cracks in 7075-T651 A1 provides evidence for a gradual transition from a fully closed crack condition at the crack tip to an essentially fully open condition at a distance of a few mm from the tip, with additional localized contact along the length of the crack. This interpretation of the data was aided by a two-dimensional, quasi-static model for ultrasonic interaction with a partially contacting interface. The model relates width and separation of asperity contacts to the frequency dependence of the ultrasonic reflection and transmission. These measurements were supplemented by tests in which water infiltrated into the crack opening. The frequency spectra of the ultrasonic transmitted signals for this case were used to estimate the average COD at various points along the crack length.