Study Of Shape Memory Mechanism And Constitutive Equation Of Shape Memory Polymer Based On Internal Stress

Shape memory polymers(SMPs)are new kinds of smart materials which could trigger shape memory effect(SME)according to the environmental conditions.The shape memory behavior is mainly triggered by temperature,electric field,magnetic field,radio wave or water.Among them,thermosensitive SMP is the most widely driver.However,the development history is short and the researchers can't thoroughly understand the microcosmic mechanisms hidden in the macroscopic appearance of shape memory behavior.The imperfect modeling of shape memory polymers severely limits its continuous development and application.The temperature / shape memory behavior of SMPs mainly comes from the release of storage strain energy which could drive the morphology change of the whole polymer.In the previous constitutive modeling,the important parameter of internal stress has not been added to the constitutive model.Under this background,from the point of view of internal stress,this paper establishes the constitutive model of SMPs under two conditions of free recovery process and external stress loading,and the modeling analysis of the newly discovered multicomponent SMP.The model is theoretically verified by the experimental data.The mechanism of solution driving which is similar to thermosensitive SMPs is also studied.In the second chapter,on the basis of Liu Yiping's phase transition theory,soft segments in SMPs are divided into frozen phase and activated phase.The activation process of the frozen segment is followed by the Eyring equation.According to the theory of thermal activation,it is considered that the driving of the internal stress leads to the reduction of the activation energy required for the freezing phase,and the internal stress is taken as a parameter into the constitutive modeling of the free recovery process,meanwhile,the physical meaning is given to the parameters of the freezing volume fraction.The theory of phase transition is improved,and the mechanism of internal stress on the SME in the process of free recovery is further studied.In the third chapter,on the basis of the theory of transient network,the relationship of stress and strain under external stress loading condition with the consideration of internal stress is first established,and the effect of loading rate is further studied.The theoretical model fits well with the experimental data at different strain rates.This article continues to reveal the characteristics of the sensitive to the strain rate during large deformation happened in double-network hydrogels based on the theory of transient network.In the fourth chapter,the Ree-Eyring model is introduced into the multicomponent SMPs.The viscoelastic and relaxation behavior of multicomponent SMPS is considered to be the result of the coordination of each unit.The polymer relaxation time is defined on the basis of the cooperative Eyring equation.In solution driving process,Arrhenius law and WLF equation are applied to the relaxation process of polymer chain under the condition of water solution under the glass transition temperature and the glass transition temperature,respectively.The effects of chemical plasticization and physical swelling on the relaxation behavior of SMPs are studied and quantified.