On the interpretation of different R-curves for soft PZT

From results of literature, it can be concluded that the R-curve of soft pi ezoelectric ceramics strongly depends on the type of test. In three-point b ending tests and measurements with compact tension specimens a pronounced R -curve is found, whereas tests with opposite roller loading show a more fla t crack resistance curve. Two possible reasons for this effect are differen ces in the domain switching state and bridging interactions in the crack wa ke. Both effects are discussed in terms of fracture mechanics. From the con siderations it can be concluded that the dominating effect is the test-depe ndent change of the orientation state in the crack wake. (C) 2001 Elsevier Science Ltd. All rights reserved.