Measurement of elastic properties during crack growth in Al203-ceramics

We employed ultrasonic techniques in order to gain information on the R-curve behavior of Al203-ceramics. A reduction in the sound velocity has been observed at the tip of subcritically grown cracks. The size of this zone is about 100 mym. The measurements were carried out by using critical angle reflectometry, time-of-flight measurements, and evaluation the V(z)-curves obtained from Scanning Acoustic Microscope. Furthermore we could also observe effects related to interaction of serrated crack walls by in-situ experiments in the Scanning Acoustic Microscope.