Piezoelectric nanocomposites composed of piezoelectric nanowires and flexible polymer have emerged as outstanding applications for flexible energy harvester. Although piezoelectric materials in their bulk form have high electromechanical coupling coefficient and can convert mechanical energy to electrical energy efficiently, they usually have low fracture toughness and are limited in applications due to difficulty in machining and casting it on to curve surfaces. Recently, additive manufacturing process (direct write) have been developed to incorporate piezoelectric nanowires into a polymer matrix with controlled alignment. It is shown that not only direct writing method can solve these issues but also it can improve the performance of the nanocomposite energy harvester significantly. In this paper, an experimentally verified finite element (FE) and micromechanics models are developed for calculation and optimization of g31 voltage coefficient of a piezoelectric energy harvester nanocomposite. It is shown that, by using high aspect ratio nanowires with controlled alignment the g31 coefficient can be enhanced more than five times compared to bulk form. Moreover, it is demonstrated that to achieve highest possible g31 coefficient only a small volume fraction of nanowires is needed and further increase in volume fraction result in the reduction of g31 coefficient.
Piezoelectric materials are currently among the most promising building blocks of sensing, actuating and energy harvesting systems. However, these materials are limited in applications due to difficulty in machining and casting it on to curve surfaces. To mitigate this issue, one method is through additive manufacturing (direct printing) of piezoelectric nanocomposite in which piezoelectric nanomaterials are embedded into a polymer matrix. Although significant progress has been recently made in this area, modeling the electromechanical response of a directly printed nanocomposite remains a challenge. Thus the objective of this study is to develop robust micromechanical and finite element models that allows the study of the electroelastic properties of a directly printed nanocomposite containing piezoelectric inclusions. Furthermore, the dependence of these properties on geometrical parameters such as aspect ratio and alignment of the active phase are investigated. The focus of this work is a demonstration of the effect gradual alignment of piezoelectric nanowires in a nanocomposite from randomly oriented to purely aligned improves the electroelastic properties of a directly printed nanocomposite. Finally, these models are verified through experimental measurement of electroelastic properties of the nanocomposites containing barium titanate nanowires in Polydimethylsiloxane (PDMS) polymer.