Modeling and Parametric Analysis of Multilayer Piezocomposite Actuators

Design space for morphing structures using single layer commercial piezocomposite actuators are often restricted due to limitations in actuation authority. Optimal designs are those in which the substrate-actuator composite is stiff enough to maintain shape when subjected to surface pressures but allow for the desired curvature under excitation. This trade-off limits substrate to actuator thickness ratios in applications where dynamic pressures are high. One way to improve actuation authority while maintaining stiffness is to use multiple piezocomposite actuators. This paper explores the benefits and drawbacks of using multilayer piezocomposite actuators. The actuators are modeled using the finite element method and are characterized using well-known free strain and blocked force conditions in a four-point loading condition. Material properties for substrate, piezocomposite, and glue layers are modeled based on previous experimental analysis of curvature over a range of thickness ratios for single element actuators. A parametric analysis is conducted on multilayer piezocomposites varying thickness ratio, substrate material and number of piezocomposite layers. Results for the parametric analysis are presented in the form of maximum curvature, work done, and work done normalized by number of layers. A discussion of new design space potential for multilayer actuators is provided.

Stimuli-responsive composite biopolymer actuators with selective spatial deformation behavior

Bioinspired actuators with stimuli-responsive and deformable properties are being pursued in fields such as artificial tissues, medical devices and diagnostics, and intelligent biosensors. These applications require that actuator systems have biocompatibility, controlled deformability, biodegradability, mechanical durability, and stable reversibility. Herein, we report a bionic actuator system consisting of stimuli-responsive genetically engineered silk–elastin-like protein (SELP) hydrogels and wood-derived cellulose nanofibers (CNFs), which respond to temperature and ionic strength underwater by ecofriendly methods. Programmed site-selective actuation can be predicted and folded into three-dimensional (3D) origami-like shapes. The reversible deformation performance of the SELP/CNF actuators was quantified, and complex spatial transformations of multilayer actuators were demonstrated, including a biomimetic flower design with selective petal movements. Such actuators consisting entirely of biocompatible and biodegradable materials will offer an option toward constructing stimuli-responsive systems for in vivo biomedicine soft robotics and bionic research.