Typical Mechanical Behavior Of Epoxy Shape Memory Polymer And Its Composite

Shape memory polymer composites(SMPC) are a new kind of smart material,compared with shape memory alloy and ceramic, it have a number of potentialtechnical advantages, such as lightweight, cheap, and high deformableability(maximum shape recovery ability can be as much as 100%). These amazingadvantages enable such materials as an ideal candidate material for the applicationin aerospace, biomedicine, intelligent bionic and so forth. Especially it has beenused widely in the space deployable structures, and has the potential to promote thedevelopment of smart structures of aerospace craft. At current, for the application ofaerospace industry, shape memory polymer and its composite are new materialswhich lack theoretical development. The mechanism behind these features, such asthe constitutive relationship, strength and post buckling analysis, have not beenclearly explored and discovered yet. As a result, the development and application ofshape memory polymer and its composite in aerospace industry has been seriouslylimited.In this thesis, the space resistant ability of epoxy shape memory polymer andits composite have been investigated through exposure the materials to atomicoxygen, ultraviolet light, thermal vacuum test and thermal cycling test. Then, theconstitutive relationship, strength of shape memory polymer and its composite havebeen completed. Finally, the analysis of post buckling deformation for SMPClaminate had been finished.The radiation tolerance of shape memory polymer and its composites wereinvestigated by exposure the materials under simulate space the atomic oxygen,ultraviolet light, thermal vacuum and thermal cycling environment. After irradiatedfor a dose of aircraft endure for a year in space, the material shows goodanti-irradiation property, the changings of microstructure, thermal property,mechanical property and shape memory property are seldom. After exposure thematerials to thermal cycling for 100 h, the mass lose less than 0.7%, the glasstransition temperature and strength of the material increased slightly, the shaperecovery ability keeps stable and the elongation decreased slightly. After irradiatedby ultraviolet light, the glass transition temperature, strength, elastic modulus ofSMP and SMPCl had a little increase; the mass lose is no more than 0.7% and theshape recovery ratio keeps 100%.After irradiated by atomic oxygen irradiation for100 h, the surface is significantly roughened which indicating that the epoxy resinhad been eroded significantly by AO. The mass loss can be reach as large as 2.7%,the yield strength, break strength and elastic modulus have a decreased about 10%.It should be noted that the strength and elastic modulus of shape memory polymercomposite are above 15 MPa and 12 GPa respectively.In this study, a constitutive model for thermoset SMP has been developed basedon the assumptions that the polymer can be partly in the rubber phase and partly inthe glass phase simultaneously and that these materials can transform from onephase to the other with the application or removal of heat. We assume equal stress,which means that the stresses in the glass phase and in the rubber phase are equaland equal to the total stress in the polymer. Hooke’s Law is used to describe themechanical characteristics of this glass phase and the rubber phase. The constitutivemodel is validated with experiments.Further, based on composite bridging model theory and the continuumthermodynamic considerations, a 3D constitutive model has been developed tosimulate the stress-strain-temperature relationship of unidirectional elastic carbonfiber reinforced SMPC. The material has been assumed as a mixture of elasticreinforcement and SMP matrix, which is further divided into a continuum mixture ofa glassy and a rubbery phase, and the fraction of each phase is complementaryvariation depending on the temperature. Using the theory of composite bridgingmodel, we then incorporate the influence of elastic fiber reinforcement in theconstitutive model. The mechanical characters of fiber, glassy phase and rubberyphase are embodied by the Generalized Hooke’s laws. Comparisons between modelprediction and experimental results are presented too.As a main component of space deployable structure, Shape Memory PolymerComposites(SMPC) are exposed to long-term periodic sharp temperature changes.It is necessary to investigate the influence of temperature on strength property ofSMPC. In this article, a micromechanical strength predication model was developedbased on composite bridging model, which was used to define the stiffness matrixand to relate the stress increment in the fiber and matrix. Furthermore, theprogressive failure strength of SMPC was simulated simply based on the propertiesof the material and the geometric parameters of the laminates. Comparison of thepredictions with the experimental measurements was carried out. As a whole, theoverall correlation between the theory and the experiments was reasonable.Furthermore, the model has been applied to predict the transverse strength, axialstrength and in-plane shear strength of different composite laminates(fiber content,ply angle) at different temperature.As a new kind of smart materials, shape memory polymer composites(SMPC)are being used in large in-space deployable structures. In order to increase therecovery force of a SMPC laminate, an alloy film was bonded on the surface of thelaminate. This paper describes the post bulking behavior of the alloy film reinforcedSMPC laminate. Based on the theorems of minimum energy, a mathematical modelis derived to describe the relation between the strain energy and the material andgeometry parameters of the alloy film reinforced SMPC laminate. The finite elementmodel(FEM) is also conducted on the SMPC laminate to demonstrate the validity ofthe theoretical method. The relation between the recovery force and the materialgeometry parameters were also investigated from the point of view of a theoreticaland FE method. Good agreement can also be observed between the theoretical andFEM results.