Shape Memory Properties Of Knitted Structural Reinforced Polymer Matrix Composites

Shape memory polymer(Shape Memory Polymer,SMP)are stimulus-responsive materials that can change shape in response to external stimuli such as light,heat,electricity,magnetism and water.Shape memory polymers have the advantages of low density,low cost,high reversible strain and ease of processing.However,their low modulus,low strength and low recovery stress limit their application.Shape memory polymer composites(SMPCs)are often reinforced with particle and fiber to achieve better mechanical and shape recovery properties.Many SMPCs which are reinforced with continuous fibers have excellent shape memory properties,however,the small stretchable strain of the continuous fibers limits the shape memory performance of SMPC under tensile and other large strain loads.Here we have taken advantage of the good ductility of knitting-fabrics to prepare thermally actuated knitting-fabric reinforced shape-memory epoxy composites and electro-activated three-dimensional lightweight knitted tubular composites.Firstly,the shape memory properties and mechanisms of anisotropic knitting-fabric reinforced shape memory epoxy composites were investigated under large tensile strains.The effect of epoxy component ratios,tensile strains,and course(0°)/wale(90°)directions on the shape memory behavior,recovery stress,and mechanical property of the shape memory epoxy(SMEP)and its composite(SMPC)were studied.The results show that the SMEPs and SMPCs with the tensile strain up to 30%have good shape fixity ratios of above 99%and final recovery ratios of above 98%.The recovery stress of the SMPC can improve up to 5.8 times as compared with SMEP.Secondly,the shape memory behavior of electro-activated three-dimensional lightweight knitted tubular composites under compressive loading has been investigated.The effects of component ratios and voltages on the electrical properties,shape recovery behavior,shape recovery force and mechanical property of the tubular composites were investigated.The results show that the bulk density of three-dimensional lightweight tubular composite was only 0.50g/cm~3.The shape fixity ratios and the shape recovery ratios were over 99%,and the recoverable compressive strain is 60%.The electro-activated shape recovery time of the tubular composites with DC voltage of 20 V is short to 12 s.The maximum recovery force can reach 3.19 N.Finally,a micro/meso/macro multi-scale finite element model for thermally actuated shape memory composites and a coupled electric/thermal/deformation finite element model for electro-activated shape memory composites were established based on a viscoelastic model and periodic boundary conditions.These models were used to simulate the temperature and shape changes during shape memory cycling and to reveal the shape memory mechanism of knitted composites.The results of this thesis will benefit the development and application of better,lighter and stronger drives in the future.