Two-Scale Model for Mechanical Analysis of Nastic Materials and Structures

Nastic actuators are high energy density active materials that mimic the working processes in the plant kingdom to produce large deformation through the conversion of chemical energy inside the materials. In these actuators, the transport of the charge and fluid across a selectively permeable membrane is controlled to achieve bulk deformation. The permeable membrane may contain biological ion pumps, ion channels, and ion exchangers surrounding fluid-filled cavities embedded within a matrix. To study the working mechanism of the nastic actuators, the coupled process of ion transport and matrix response in nastic materials is characterized at two-scales by developing and solving biological transport models at one scale that are coupled with a finite element model of the matrix at a much larger scale. The emphasis is mainly focused on the mechanical analysis of the multi-actuators array structures. To increase the computational efficiency, the analysis of a nastic structure with multi-actuators is performed using an appropriate homogeneous method. A two-scale model is developed to simulate the mechanical response of the structure composed of multi-actuators. Numerical results are shown to illustrate the validity and efficiency of the proposed method.