Initiation and propagation of cracks in piezoelectric ring under non-uniform mechanical loading

Initiation and propagation of cracks in lead zirconate titanate (PZT) piezoelectric rings under a non-uniform mechanical loading were studied. The PZT ring was sandwiched between two pieces of metals and then compressed by a torque. Bolt clamping produced a non-uniform external stress on the PZT ring and caused various degree of depoling at different positions of the ring. A large torque also initiated cracking and breaking in the ring. Fracture features of the broken PZT ring were observed using scanning electron microscopy (SEM). Fracture toughness at the inner part of the ring changed significantly due to 90° domain rotation after a large torque had been applied. The ratio between the fracture toughness along the thickness direction and the fracture toughness along the radial direction varied from >1 to <1 due to loading. Cracks originated from the defects of the inner part of the ring and propagated mainly along the direction of low fracture toughness.