Lead zirconate titanate (PZT) multilayer actuators with an interdigital electrode design were studied under high electric fields (3 and 6 kV/mm) in a unipolar cycling mode. A 100 Hz sine wave was used in cycling. Five specimens tested under 6 kV/mm failed from 3.8 × 105 to 7 × 105 cycles, whereas three other specimens tested under 3 kV/mm were found to be still functional after 108 cycles. Variations in piezoelectric and dielectric responses of the tested specimens were observed during the fatigue test, depending on the measuring and cycling conditions. Selected fatigued and damaged actuators were characterized using an impedance analyzer or small signal measurement. Furthermore, involved fatigue and failure mechanisms were investigated using scanning acoustic microscope and scanning electron microscope. The extensive cracks and porous regions were revealed across the PZT layers on the cross sections of a failed actuator. The results from this study have demonstrated that the high-field cycling can accelerate the fatigue of PZT stacks as long as the partial discharge is controlled. The small signal measurement can also be integrated into the large signal measurement to characterize the fatigue response of PZT stacks in a more comprehensive basis. The former can further serve as an experimental method to test and monitor the behavior of PZT stacks.
Palladium nanoparticles were synthesized directly in solid fluoropolymer films by thermal decomposition of a palladium acetylacetonate precursor molecularly infused in the fluoropolymer matrix. This chemical infusion synthesis technique was studied using transmission electron microscopy along with selective area electron diffraction to gain insight into the nucleation and growth of palladium nanoparticles. Formation of palladium nanoparticles can be correlated with defects in the polymer matrix as well as their associated free volume such that a relationship between average particle size and mean free volume fraction can be constructed. At low processing temperatures, the average particle radius increases monotonically with the processing time but more complicated variations occur for longer times. The growth of nanoparticles was interpreted using a modified diffusion-limited growth model. While nearly monodisperse nanoparticles dispersed throughout the polymer volume were obtained at low processing temperatures, surface percolation of nanoparticles was observed at relatively high temperatures owing to high precursor decomposition and diffusion rates.
Laser ultrasonic techniques can be used to study the ultrasonic properties of nuclear graphites and can serve as tools in establishing relationships between materials microstructure and the macroscopic stiffnesses of graphite. Establishing structure-property relationships permits improved ultrasonic sensing of graphite microstructural changes related to service-induced degradation. Laser ultrasonic measurements were made using a pulsed Nd:YAG laser source and detection was performed using a Michelson-type interferometer. This source-receiver combination provides for non-contacting, highly linear transduction of broadbanded, ultrasonic pulses permitting simultaneous determination of longitudinal and shear stiffnesses. Measurements show that among the graphites examined, a change in density of 0.21 g/cm 3 (average 1.8 g/cm 3 ) results in a change in the longitudinal elastic stiffness of 7.1 GPa (average 12.2 GPa) and 3.2 GPa (average 4.3 GPa) for the shear stiffness. Larger variations in density were produced by controlled oxidation of IG-110 and NBG-18. Shear wave birefringence measurements using laser line sources in IG-110 and PCEA indicate that IG-110 behaves isotropically while PCEA displays texture characteristic of transversely isotropic materials.
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