Property Characterization And Meso-mechanical Analysis Of Smart Structures With Damages

Smart structures have attracted more and more attention due to their dual properties of conventional composite structures and of functional composite structures, and are applying or to be applied in some fields such as aeronautics & astronautics, national defense, architecture, medicine. Among them, shape memory alloy (SMA) reinforced smart structures could be used to do self-adaptive structural shape and strength and to prevent structure failures. Although many researches on SMA smart structures without damages have been made, however, researches on SMA smart structures with damages have rarely reported thus far. In this dissertation, researches on material property, meso-mechanical behavior characterization, and damages detection have been emphatically made, and some valuable results have been obtained, with the aim of providing a theoretical basis and experimental data for further studying on failure prevention and integrity evaluation of smart structures.The novel researches done in this dissertation include:1) Experimental methods for NiTi-SMA are proposed based on the SMA material evaluation technology and requirement of adaptive structures, and experiments on NiTi wires have been performed. Some useful experimental results are presented herein.2) Based on the method of hysteresis element, the a - e relation of NiTi-SMA has been obtained for tensile tests, and numerical simulations are in good agreement with experimental results.3) A novel Martensitic transformation kinetics model for SMA is proposed based on the phenomenological description of the Martensitic transformation heat flow-temperature curve and on the linear relationship between the partial derivatives with respect to the temperature of Martensite fraction and of Gbbis free energy. Numerical simulations by utilizing the proposed model are closer to experimental results than those from other models.4) As is noticed that the thermodynamics nonlinear equation of SMAs is very complicated and difficult to obtain the solution due to variables nested each other, a simple method starting from martensite fraction has been proposed to solve the equation. Numerical example indicates that the proposed method is simple and accurate, and may find its application in engineering applications.5) A one- dimensional meso-mechanical model is developed to describe the longitudinal stiffness reduction and thermo-dilatation variation of the composites caused by fiber breaking or by fiber peeling off the base material. Incrementalconstitutive relation is then established for SMA fiber reinforced smart structures with damages by introducing three parameters to describe the extents of fiber breaking, fiber peeling off the base material and interface weakening.6) The thermo-mechanical behaviors of SMA fiber reinforced smart structures with damages have been analyzed by utilizing the shear lag model and variational principle. Mathematical expressions on meso-displacement field, stress-strain field of typical element with damages have been presented, and a failure criterion of interface between SMA wires and base material is established. A geometric characterization on the failure criterion has also been made via an example.