GROWTH OF INDENTATION CRACKS IN POLED AND UNPOLED PZT

The growth behaviour of indentation cracks in both poled and unpoled P ZT is examined by subjecting the cracks to static and cyclic loading i n bending. An anomalous growth of the cracks not subjected to any dire ct stressing was observed during cyclic fatigue loading in both the po led and unpoled materials. In the poled PZT specimens the length of th e radial indentation cracks was found to be strongly dependent on thei r 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 an isotropy with respect to the direction of poling is not entirely consi stent with,previously proposed interpretations, and an alternative exp lanation is suggested. (C) 1997 Elsevier Science Limited. All rights r eserved.