Growth of indentation cracks in poled and unpoled PZT

The growth behaviour of indentation cracks in both poled and unpoled PZT is examined by subjecting the cracks to static and cyclic loading in bending. An anomalous growth of the cracks not subjected to any direct stressing was observed during cyclic fatigue loading in both the poled and unpoled materials. In the poled PZT specimens the length of the radial indentation cracks was found to be strongly dependent on their orientation with respect to the poling direction, in agreement with previously reported observations The growth behaviour of the cracks is discussed after having estimated the magnitude of their total stress intensity factor. It is argued that the apparent fracture toughness anisotropy with respect to the direction of poling is not entirely consistent with,previously proposed interpretations, and an alternative explanation is suggested. (C) 1997 Elsevier Science Limited. All rights reserved.