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The Rmomechanical Properties of Shape Memory Polymer and Its Smart Structures

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Tutor: YangQingSheng
School: Beijing University of Technology
Course: Mechanics
Keywords: Smart material and structure,Shape memory polymer,Constitutive model,Hinge struc
CLC: TB381
Type: Master's thesis
Year:  2013
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As a class of novel smart materials, shape memory polymers (SMPs) have agreat potential for application in actuator materials after the shape memory alloys,which have the merits of low density, low cost, large deformation, adjustable criticaltransition temperature and partly biocompatible and biodegradable. SMPs have beenwidely used in design of deployable structures, medical devices as well as smartclothes, and are expected to be used in smart sensors, actuators, control componentsand other smart devices in the future. Shape memory effect of SMPs is implementedthrough their phase transformation induced by stimulating fields among whichthermal field is the most frequently used. Therefore, understanding thermo-mechanicproperties of SMPs is crucial to their in-deep study and application development.However, mathematical description of the mechanism, also referred to as constitutivemodel, in macroscopic and microscopic are still in process. And the analysis methodscorresponding to the constitutive models are still the key points. Theoretical andnumerical researches were carried out in this study to investigate thermo-mechanicaland shape memory behaviors of SMPs and their structure (deployable hinge). Thedetails are listed as follows.(1) A three-dimensional thermo-mechanical constitutive model, includingstress-strain-temperature model and material parameters evolution models, wasproposed for isotropic SMPs. Based on the present experiment and constitutivemodels, by considering the elastic, viscoelastic and thermal deformation of isotropicSMPs, a segmented three-dimensional form of thermo-mechanical constitutiveequation for isotropic thermal actuated SMPs was developed, with defined physicalsignificance. And the fitting method for key parameters is provided.(2) A finite element procedure based on the present constitutive model isimplemented to analyze complicate SMP structures. Firstly, implement the segmentedthree-dimensional model into user material subroutine (UMAT) in ABAQUS platform.Secondly, testify the effectiveness of SMP numerical method by uniaxial tensilemodel and cantilever beam bending model tests. Finally, indentation of a SMP bodywas adopted to investigate the shape memory effect process.(3) Analysis of intelligent hinged shell structures: deployable deformation andshape memory effect. Firstly, the influences of hinge structure parameters, i.e.structure length, structure angle, arch length, on the nonlinear loading process wereinvestigated. Discussed different factors affected by each parameter. Secondly, thetotal shape memory processes of the hinged structure, including loading in hightemperature, decreasing temperature with load-carrying, unloading in low temperature and recovering the initial shape with increasing temperature, are illustrated.(4) SMP internal fixation device and its extension device, also named as SMPactive disassembly device, are designed. Firstly, referencing SMP hollow bucklestructure design example, a SMP internal fixation device is designed. Interchangebetween design model and assembly model of SMP internal fixation device, anotherSMP active disassembly system is introduced. Furthermore, based on the numericalmethod, working process of these two devices, ie. shape memory effect inthermodynamic cycle process, are analyzed, which provide key design issues thatneed to be attention in preliminary design and useful guidance for subsequentimprovement.
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