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This paper describes an experimental and analytical study on the static fatigue behavior of piezoelectric ceramics under electromechanical loading. Static fatigue tests were carried out in three-point bending with the single-edge precracked-beam specimens. The crack was created perpendicular to the poling direction. Time-to-failure under different mechanical loads and dc electric fields were obtained from the experiment. Microscopic examination of the fracture surface of the piezoelectric ceramics was performed as well. A finite element analysis was also made, and the applied energy release rate for the permeable crack model was calculated. The effect of applied dc electric fields on the energy release rate versus lifetime curve is examined. The most important conclusion we reach is that the lifetimes for the piezoelectric specimens under a positive electric field are much shorter than the failure times of specimens under a negative electric field for the same mechanical load level.

In this paper, we present a microelectromechanical systems (MEMS)-based multimode low-frequency piezoelectric energy harvester (PEH), which can operate at low resonant frequencies (i.e., [Formula: see text][Formula: see text]Hz). The proposed harvester has a symmetric serpentine structure with a doubly clamped configuration comprising several proof masses at the junctions. The optimal parameters of the proposed energy harvester are determined by a computerized optimization technique based on a genetic algorithm (GA). Finite element simulations showed that the optimization results can generate high voltage with two usable low-frequency resonant frequencies. Furthermore, we discuss the array structure based on the proposed PEH. Finite element simulations demonstrate that our piezoelectric MEMS harvester array can generate voltage with a frequency ranging from 110.95 to 157.84[Formula: see text]Hz. Its normalized power density (NDP) when operating in the first four modes is 1284, 932, 1978, and 2592 [Formula: see text]Wcm[Formula: see text] m[Formula: see text]s4, respectively, and its performance outperforms those of previously reported MEMS-based energy harvesters.

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Polymers are often combined with magnetostrictive materials to enhance their toughness. This study reports a cellulose nanofiber (CNF)-based composite paper containing dispersed CoFe2O4 particles (CNF–CoFe2O4). Besides imparting magnetization and magnetostriction, the CoFe2O4 particles increase the fracture elongation of the CNF–CoFe2O4 composite paper, although the ultimate tensile strength of the composite paper decreases with increasing CNF content. As strength and toughness are usually inversely proportional, it was inferred that the magnetostrictive CNF–CoFe2O4 composite paper has good toughness.