Piezoelectric materials, by virtue of their unique electromechanical characteristics, have been recognized for their potential utility in many applications as sensors and actuators. However, the sensing or actuating functionality of monolithic piezoelectric materials is generally limited. The composite approach to piezoelectric materials provides a unique opportunity to access a new design space with optimal mechanical and coupled characteristics. The properties of monolithic piezoelectric materials can be enhanced via the additive approach by adding two or more constituents to create several types of piezoelectric composites or via the subtractive approach by introducing controlled porosity in the matrix materials to create porous piezoelectric materials. Such porous piezoelectrics can be tailored to demonstrate improved signal-to-noise ratio, impedance matching, and sensitivity, and thus, they can be optimized for applications such as hydrophone devices. This article captures key results from the recent developments in the field of computational modeling of novel piezoelectric foam structures. It is demonstrated that the fundamental elastic, dielectric, and piezoelectric properties of piezoelectric foam are strongly dependent on the internal structure of the foams and the material volume fraction. The highest piezoelectric coupling constants and the highest acoustic impedance are obtained in the [3-3] interconnect-free piezoelectric foam structures, while the corresponding figures of merit for the [3-1] type long-porous structure are marginally higher. Among the [3-3] type foam structures, the sparsely-packed foam structures (with longer and thicker interconnects) display higher coupling constants and acoustic impedance as compared to closepacked foam structures (with shorter and thinner interconnects). The piezoelectric charge coefficients (dh), the hydrostatic voltage coefficients (gh), and the hydrostatic figures of merit (dhgh) are observed to be significantly higher for the [3-3] type piezoelectric foam structures as compared to the [3-1] type long-porous materials, and these can be enhanced significantly by modifying the aspect ratio of the porosity in the foam structures as well.

A framework for understanding the structure (shape memory and thermomechanical)–property relationships in shape memory polymers (which could be reasonably modeled as comprising of a soft phase and a hard phase) using indentation is developed. A finite element model is developed to predict the complete stress–strain–temperature characteristics of shape memory polymers under uniaxial and indentation loading conditions. By invoking the indentation load–depth response characteristics for a range of temperatures, it is demonstrated that the indentation method predicts the variation of the mechanical properties of shape memory polymers (i.e., elastic modulus) as a function of temperature and microstructural state (i.e., ‘glassy’ vs. ‘rubbery’) for materials that exhibit a wide range of transitions (i.e., gradual and sharp). By invoking the indentation deformation characteristics of shape memory polymers for a range of indenter geometries and temperatures, it is demonstrated that the extent of shape recovery is strongly dependent on temperature, microstructural state and constraint loads. By invoking the spatial evolution of stresses during the indentation deformation process and the subsequent recovery process, it is demonstrated that the increase in the internal stresses during the deformation process and the rate of dissipation of the internal stresses during the recovery process is dependent on the indenter geometry and temperature. The predictions of the finite element model for the variations of the mechanical properties and shape recovery characteristics of shape memory polymers with temperature are in reasonable agreement with the trends observed in experiments.