Real cracks are often subjected to the action of externally applied or residual compressive stress fields, the spatial distribution and intensity of which may depend considerably on the particular configuration or the history of the cracked material system. A compressive stress can significantly alter the probability of detecting a crack-like defect by means of ultrasonic waves by bringing the crack faces in contact, reducing in this way the material discontinuity to which an ultrasonic wave is sensitive. The degree to which a compressive stress causes crack closure depends, in addition to its intensity and spatial distribution, also on the roughness of the crack faces and on their degree of conformity. Modeling the scattering of an incident elastodynamic wave from a crack with partially contacting interfaces must account for all these factors.
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