Observation of stable crack growth in AL203-ceramics by acoustic microscopy and acoustic emission

In certain ceramics one observes an increase in crack resistance with increasing crack length (R-curve behaviour). This phenomenon is explained by two controverse models: 1) the crack resistance grows by an increase of microcrack density at the crack tip; 2) the crack resistance grows by the interaction of the serrated crack surfaces behind the crack tip. The crack grawth in Al2o3-ceramics has been studied by Scanning Acoustic Microscopy (SAM) and Acoustic Emission (AE). The results of both methods show that both increase of microcrack density and interaction of crack surfaces occur and should play a role in increasing the crack resistance.