Study On Shape Memory Mechanism Of Ultra-High-Molecular-Weight Polyethylene Composites

With the coming of intelligent era,intelligent materials enter people’s life.As a kind of intelligent materials,shape memory polymer(SMP)is bound to become one of the main development directions in the future,and also one of the necessary conditions for entering the intelligent era.After nearly 80 years of development,the application of SMP in aerospace,biomedical,smart home appliances and other fields is in the ascendant.In the future,SMP will still be one of the hot spots in the application field,and will also be one of the key technologies to promote the development of national economy.In this research,ultra-high-molecular-weight polyethylene(UHMWPE)is used as the matrix material,and reinforced SMP with higher shape memory performance is obtained to solve the performance defects of SMP in the application process.At the same time,single screw extruder is used to prepare the samples with molecular chain orientation structure,and the influence of molecular chain orientation on the shape memory effect is further studied.Specifically,the research mainly includes the following 5 aspects:1.Calcium stearate(CS)and polyethylene wax(PEW)are used as solid lubricants to improve the fluidity of materials and reduce micro defects.Besides,the effects of CS and PEW content on the entanglement of UHMWPE molecular chains,mechanical,thermal and shape memory properties is explored.Moreover,the shape memory effect of UHMWPE was analyzed from the perspective of molecular chain entanglement and distribution of crystalline region,and the evolution mechanism of microstructure of solid lubricant modified samples in the shape memory process was explored.2.UHMWPE nanocomposites were prepared by adding carbon nanotubes(CNTs)and graphene(GNPs),and their properties were studied.The effects of nano particle dispersion on the thermal,mechanical and shape memory properties of the nanocomposites were analyzed.The influence mechanism of different microstructure nano materials on the shape memory properties of UHMWPE nanocomposites is explained.The preparation method of adding nano-materials to UHMWPE provides a method for the preparation of high performance shape memory materials.3.The differences between molding and extrusion were analyzed and compared.Combined with the characteristics of extrusion,SMP with different molecular chain orientation were prepared,and the effect of molecular chain orientation on shape memory properties was studied.The evolution mechanism of three-phase microstructure in the shape memory process is analyzed.The preparation of SMP with molecular chain orientation structure provides a new idea for obtaining SMP with high shape memory performance.4.Based on the viscoelastic theory and the deformation mechanism of SMP microstructure,the physical model and mathematical model for characterizing the shape memory process of UHMWPE is constructed,and the three-dimensional isotropic thermodynamic constitutive equation is established by combined with the micro deformation mechanism of SMP.Then,the material parameter equation suitable for describing the thermodynamic behavior of UHMWPE is proposed according to the experimental data.5.A material interface subroutine suitable for SMP is programmed based on the secondary development of ABAQUS software.The finite element method is used to solve the thermodynamic coupling problem in the shape memory process,and the shape memory curves for characterizing the tensile shape memory properties are obtained.Compared with the experimental results,the correctness of the thermodynamic constitutive model is verified.Besides,the effects of the switching tempeature,strain and step time on the shape memory properties are further analyzed.