Analysis of the bending fracture process for piezoelectric composite actuators using dominant frequency bands by acoustic emission

We examined the fracture process of a thin monolithic PZT and a plate-type piezoelectric composite actuator (PCA) subjected to a three-point bending load with the aid of an acoustic emission (AE) monitoring. Fracture surface observations were conducted using a scanning electron microscope (SEM) and optical microscope. AE signals were analyzed during the bending fracture process of a PCA in terms of the dominant frequency band which was processed by a fast Fourier transform (FFT) along with the behavior of AE amplitude. Three dimensional finite element simulations were performed to investigate the stress state in each layer of PCAs. It was concluded that the damage of a PCA under a bending load was initiated in the brittle PZT layer, which induced the interlaminar delamination between PZT layer and adjacent fiber composite layers. As a bending load approached maximum, fiber breakages hindering the main crack propagation in the glass–epoxy bottom layer together with macro-delamination between the PZT and fiber composite layers led to the final failure of PCAs. The fracture process and mechanisms of PCAs were successfully identified by AE characteristics based on the analysis of dominant frequency bands.