Propagation of ultrasonic plane waves in a plastically deformed medium

The detection and sizing of cracks during inspection of structures is typically achieved by ultrasonic techniques; both time-of-flight and scattered amplitude techniques are employed. However, when a component containing a fatigue grown crack is unloaded, a zone of reverse (Compressive) plastic deformation forms near the crack tip and a certain part of the crack is "closed" (in contact) over an undetermined length. Thus the ultrasonic waves pass through the closed crack faces and one obtains an underestimate of the crack size which leads to a nonconservative reliabililty analysis. If, however, the region of plastically deformed material can be identified, it would be possible to determine a better estimate of the size of the crack. Towards this end, we first explore the effect of plastic deformation on the propagation speed of the ultrasonic waves. We examine the effect of plastic deformation on the propagation of ultrasonic plane waves and the explore the propagation in the plasticall y deformed region near a crack.