Fabrication And Characterization Of Shape Memory Auxetic Foams

Take advantage of high shear modulus,good notch resistance,good fracture toughness,fatigue resistance,high absorption energy,auxetic foams have potential applications in many fields.For example,auxetic foams can be used as fillers for sandwich structure in space industry.Shape memory polymer(SMP)is an intelligent material with initial shape memory function.Integrating the excellent performance of other materials,SMPs can provide a new solution for solving complex engineering problems.Therefore,in this paper,shape m emory epoxy polyurethane composite foam was synthesized by the reaction foaming method,where polyurethane foaming was used to prepare porous scaffold and shape memory epoxy,as functional phase,formed an interpenertrating structure with polyurethane;After multiaxial compression,the temporary structure of the cured shape memory foam had negative Poisson's ratio effect;In the foaming process,the shape memory auxetic foam,whose initial structure had negative Poisson's ratio,was obtained by multiaxial compression and two-step solidification.SEM,DSC,DMA and TGA were used to characterize the microstructure,glass transition temperature and thermal stability of two kinds of auxetic foams.The compression experiments on the shape memory composite foams were carried out,including the initial structure and the temporary structure with negative Poisson's effect.The elastic modulus of the negative Poisson's ratio structure is lower than that of the initial structure.In addtion,the mechanical behaviors of the post-cured auxetic foams were studied by mechanical tensile and compression tests at normal temperature,and the relationship between the mechanical properties and microstructure in the process of tension and compression was explained.Because of two-step solidification,the microstucture of the permanent auxetic foams was not unifoam.Some re-entrant structure was not obvious while some bubble holes were queezed together,which might lead to the decrease of the negative Poisson's ratio effect.The Poisson's ratios of post-cured auxetic foams was measured by digital camera and MATLAB image processing technology to a minimum of-0.39.The post-cured auxetic foams had good shape fixed ratio,recovery ratio,the Poisson's ratio of which remained stable after repeated shape memory process.Finally,the heat driven and light driven methods were successfully used to recover the composite foams,and the fixed-point and contactless drive was realized by doping carbon nanotubes in the foams.