Study On Deformation Behavior And Deployable Structure Of Shape Memory Polymer Composites

Shape memory polymer composites(SMPCs),which combine the shape memory effect of shape memory polymers(SMPs)and the excellent mechanical properties of reinforcement phase,has gradually become a research hotspot of space deployable structures.However,there is a lack of research on the deformation behavior and damage mechanism of SMPC.Accordingly,the design of space deployable structure lacks theoretical basis,which limits its application in aerospace engineering.Under this background,a shape memory epoxy resin resistant to space environment was selected to prepare SMP and its composites.On the basis of characterizing the mechanical properties and parameters of the material,the mechanical theoretical models of in-plane buckling and out of plane buckling of fiber-reinforced SMPCs were established.In addition,the deformation behavior of an SMPC-based Ω-shaped structure was analyzed.Finally,the SMPC-based lenticular tube was designed based on the Ω-shaped structure.After the performance test,it was assembled to the flexible solar array and successfully completed the on-orbit deployment verification.Firstly,the dynamic thermodynamic properties,static tensile and shear properties of epoxy based SMP were characterized,and the important performance parameters such as glass transition temperature,tensile strength and shear strength were obtained.Furthermore,unidirectional fiber reinforced and fiber cloth reinforced SMPCs were prepared.The mechanical properties and parameters of the two composites were systematically studied by means of dynamic thermomechanical analyzer,static mechanical test system and scanning electron microscope.and the effects of temperature on the mechanical properties and damage modes of SMP and its composites were revealed.Secondly,the deformation theoretical model of in-plane buckling of fiber-reinforced SMPC was established,and the key parameters and their evolution laws during the bending process were given.The effects of temperature,thickness and fiber volume content on critical buckling curvature,strain energy,half wavelength and amplitude were investigated.Whether the fiber will buckle was mainly affected by temperature and fiber volume content,which was independent of thickness.It was found that there are three damage modes of inplane buckling,including matrix cracking,interlayer delamination and fiber tensile fracture.At the same time,the relationships between damage mode,damage limit and material parameters were quantitatively given.Then,considering the compressive strain of the matrix in the compression zone,the strain energy of the two damage systems of matrix shear cracking and fiber fracture were derived,and then the key parameters of the system were obtained by using the minimum energy principle.In addition,the analytical expressions of the key mechanical parameters in the bending process were derived,and the evolution law were revealed.The bending experiment of unidirectional fiber reinforced SMPCs verified the correctness of the theoretical model.Then,the deformation theoretical model of out of plane buckling of fiber-reinforced SMPC was established,and the key parameters in the deformation evolution process were given and compared with the in-plane buckling system.Considering the matrix compressive strain in the compression zone,the strain energy of the undamaged system is established,and the key parameters such as the position of the neutral layer,half wavelength and amplitude are obtained.The strain energy,bending moment and equivalent bending stiffness of out of plane buckling are larger than those of in-plane buckling,but the half wavelength and amplitude were smaller.At the same time,out-of-plane buckling had more fiber buckling fracture damage mode than in-plane buckling.In addition,the relationship between damage limit of out-of-plane buckling and material parameters was quantitatively analyzed.The strain energy of matrix shear cracking in compression buckling zone and fiber fracture in tension zone were derived.The expression of key parameters was obtained by using the minimum energy principle.Besides,the deformation behavior of an SMPC-based Ω-shaped structure was studied.The buckling deformation theory was introduced into the analysis of Ω-shaped structure based on unidirectional fiber-reinforced SMPC,and the safe allowable areas of arc radius and thickness under different fiber volume contents in the design were determined.On the other hand,the deformation of a Ω-shaped structure of fiber cloth reinforced SMPC was tested and analyzed.It was found that there are two damage behaviors: compression surface matrix cracking and interlayer delamination.The damage mechanisms were the matrix shear deformation between fiber layers and the matrix shear deformation at the overlap of fiber bundles.The damage behaviors did not cause fatal damage to the shape memory performance.After 10 deformation tests,the recovery ratio could still remain above 90%.Moreover,the initial damage location and influencing factors of the two damage behaviors were theoretically analyzed.The finite element analysis results were in good agreement with the theoretical analysis results,which verified the correctness of the theoretical analysis.Finally,the SMPC-based lenticular tube was designed and analyzed based on Ω-shaped structure.The structural parameters of lenticular tube were designed through the damage limit,structural stiffness and storage ratio.The variations of the temperature on the natural frequency of the structure were explored through theory,experiment and finite element simulation.The infrared thermal imager and three-dimensional full-field strain measurement system were used to analyze the evolution of the surface temperature distribution and the recovery strain during the recovery process.After 10 thermomechanical deformation cycles,it was found that it had good repeatability and high recovery ratio.The mechanism of high recovery ratio was that the cavity bulged in the recovery tail period,the driving force increased,and the structure recovered to steady state.After the performance test on the ground,it was assembled on the flexible solar array,and the deployment verification was successfully completed on geosynchronous orbit.