Fracture behavior of piezoelectric materials

Closed form solutions for all three modes of fracture for an infinite piezoelectric medium containing a center crack subjected to a combined mechanical and electrical loading were obtained. The explicit mechanical and electrical fields near the crack tip were derived from which the strain energy release rate and the total potential energy release rate were obtained by using the crack closure integral. The suitability in using the stress intensity factor, the total energy release rate, and the strain energy release rate as the fracture criterion was discussed.; Mode I fracture tests were performed on PZT-4 piezoelectric ceramics to verify the validity of the strain energy release rate as a fracture criterion for piezoelectric materials. Experimental results indicated that crack extension could be aided or impeded by the electric field depending on the field direction. The crack closure integral together with the finite element analysis was introduced to calculate the strain energy release rate in different directions from the crack tip. It was found that the crack extension direction coincided with the direction of maximum strain energy release rate.; As a part of Mode I fracture test, Vickers indentation tests were performed. An attempt was made to relate Vickers indentation test with analytical solutions for a center cracked infinite plate with far field loadings. Unsymmetric three point bending tests were performed to verify the validity of the strain energy release rate for mixed mode fracture. Crack growth trajectory was traced with an assumption that crack growth occurs to the direction of maximum strain energy release rate.