The relationship between electromechanical cyclic loading and the performance degradation of a smart bending piezoelectric actuator

This paper presents the relationship between electromechanical cyclic loading and the performance degradation of a smart bending piezoelectric actuator under a fully reversed condition. For this, the authors have fabricated two types of smart bending piezoelectric actuators, PCA and PCAWB, and then cyclic tests with different loading conditions have been carried out with a sinusoidal loading waveform at the resonant frequency along with monitoring of their performance degradation. The displacement performance and the cyclic-induced damage process of the actuators have been measured and monitored to assess their health. Comparisons between purely electric loading and electromechanical loading were made in relation to the performance degradation. The results revealed that the damage to the actuators began in the PZT layer in the form of transgranular fracture and then local intergranular cracking grew on the PZT surface. In particular, the intergranular cracking propagated along the center line of the PZT surface, where virtually maximum bending stresses took place, and sometimes extended transversely into the internal PZT layer thereby inducing a large performance degradation of the actuators. Final failure was observed only in PCAWB under electromechanical loading because of wear and a local discharge between the crack faces. The performance degradation rate for PCA was even smaller than that for PCAWB because the protective bottom layer retarded the growth of transgranular fracture in the PZT layer and impeded cracks from propagating in the PZT ceramic layer. The electromechanical cyclic cases were worse for both PCA and PCAWB than the electric cyclic cases, i.e. greater damage such as intergranular fracture, frictional wear, and sliding between the transverse cracking faces was inflicted on the PZT layer in the electromechanical cyclic tests.