Study On Model And Multiscale Algorithm For Coupled Chemo-Mechanical Behavior Of Nastic Materials And Structures

In the natural world, some plants like the Mimosa, Sunflower and venus Flytrap, can generate localized movements in response to external environmental stimuli through a biological process named nastic motion. In this motion, the biolocical ion transport makes the water to flow into or out of the motor cells imbedded in the structure, which can be regard as the muscles of the biological system. With these inspirations, a novel biomimetic smart material, i.e. a nastic material, has been developed to design advanced actuators in recent year. The nastic materials are considerd to be high energy density actuators that convert chemical energy stored in bio-fuels to generate mechanical forces. Researches indicate that the nastic materials can not be only ultisized to design high-performance shape adaptive smart actuators, but also be ideal for biomedical application such as targeted vaccine delivery. Howerver, nastic materials are still a new phenomenon, and the accessible literatures about nastic materials are still sparse. So, the related investigations will be of great importance for theoretical procgress and engineering applications.Firstly, a coupled Chemo-mechanical model is developed to simulate the mechanical and biological response of the nastic materials and structure. The nastic material considered is composed of closed liquid cell structures and synthetic membranes. Many types of biological channels, such as the ion pumps, ion channels and ion cotransporters, are embedded within the membrane to transport the species across it. Based on the theory of the nastic movement, we firstly study the mechanical response of the matric and the whole process of the ion transporting of the membrane based on a single nastic actuator. The aim is to validate the effectiveness of the coupled multiphysical model developed. Furthermore, we studied the sensitivities of the various input parameters, such as the initial solute concentrations, which have a big influence on the deformation and response time of the nastic actuators. At last, we developed a new coupled model to perform the mechanical analysis of the nastic structures with multi-actuators, and some numerical results are given to validate the models developed.Due to the fact that the nastic mateirals generally consist of a large number of micro actuators, it is always a difficult task to perform the multiphysical simulation of the nastic structures by the general numerical methods or the classic experiments. To overcome these difficulties, we establish a two-scale model to calculate the nastic structures with microcapsules periodically distributed inside in. The effective coefficients of the nastic unit cells with closed fluid inclusion inside, such as the effective elastic constants and the effective bending properties, is numerically calculated with the homogenization analysis. With these coefficients, we developed a coupled two-scale model (CTSM), which combining the two-scale model with the biological ion transport model mentioned above, to simulate the transient multiphical response of the nastic structures with multiscale features.Secondly, an extended multiscale finite element method (EMsFEM) is proposed for the mechanical analysis of the closed liquid cell materials. This tpye of functional materials contained microscopic fluid filled inclusions and the nastic materials are a special case of them. Due to the fact that the fluid inside the close cells general imcompressible, the strong boundary effects will be indueced and the errors of the results will become larger when the conventional four-node quadrilateral coarse-grid elements are utlized in the EMsFEM. Thus, a type of higher order coarse-grid elements which are more reasonable and can predicate the structural deformation more accurately of the closed liquid cells are developed. Moreover, the periodic boundary conditions (PBCs), which are inspired by the PBCs used in the homogenization method (the RVE method), are proposed to constructe the numerical base functions of the coarse-grid elements. A consistency test is carried out to validate the new boundary conditions, and the numerical results indicate that a good consistency can be obtained between the macroscopic coarse element constructed by the MEsFEMs with PBCs and the element generated by the conventional homogenization method.Furthermore, a3D extended multiscale finite element method (3D-EMsFEM), is developed to perform the mechanical analysis of nastic structures which periodically consists of the microcapsules. Accordingly, the techniques of the high order coarse-grid element and the corresponding high order PBCs, are introduced for the construction of the numerical base functions and improve the accuracy of the3D-EMsFEM.. Furthermore, a Coupled EMsFEM (CEMsFEM) which combines the ion transport model is proposed to predicate the active response of the nastic structures. The results indicate that the coupled method developed not only can track the reactions of the ion transporters of the active membrane, but also can calculate the transient mechanical response on the fine scale with the downscaling computation.On the other hand, an EMsFEM is developed to solve the mechanical behaviours of heterogeneous materials with randomly distributed polygonal microstructure. To improve the accuracy of the method, a type of rational oversampling technique is imposed to calculate the oscillatory boundary conditions for the construction of multiscale base functions. A mixed extended multiscale finite element method, which combines the EMsFEM and the standard FEM into a same model, is developed. In the method, the regions with multiscale features are modeled by the multiscale coarse-grid, while the region without multiscale features or the domains that need a high-precision computation are directly meshed by the general finite elements.At last, a new multiscale shape and topology optimization method is presented to design the closed liquid cell materials based on the EMsFEM. The multiscale optimization method firstly focuses on seeking the optimum geometrical parameters of the closed liquid cells at the microscale in terms of maximize the macroscale mechanical response of the structure. Moreover, based on the EMsFEM, a multiscale topology optimization method is further developed to optimize the distributions of closed liquid cells with objective on minimize system compliance. In this topology optimization method, the design domain is discretized by the multiscale coarse elements, while a SIMP-based density approach is employed to interpolate the equivalent stiffness matrix of the coarse-grid element. Ultimately, due to the fact that non-uniform volume expansions of the fluid in cells can induce the elastic action, the multiscale topology optimization method is extended to design biomimetic compliant actuators of the closed liquid cell materials. The multiscale optimization methods developed are implemented in the FE-package SiPESC, and numerical examples are carried out to validate the accuracy of these methods.