A Study On The Thermomechanical Properties Of Shape Memory Polymer

Shape memory polymer(SMP),known as new intelligent materials,are applied in many fields,e.g.,textile,biochemistry,aviation and aerospace,because of its advantages such as good shape memory effect,light weight and easy forming,and receive world attention recently.In this paper,based on the viscoelastic theory and fractional calculus theory,new constitutive model is built to characterize the mechanical response of shape memory polymer,and meanwhile the shape memory process of SMP is simulated by using finite element method of viscoelastic analysis.Main contents are as follows:Firstly,fractional calculus Poynting-Thomson model is used to investigate the viscoelastic response of SMP.Fractional calculus-based constitutive equations are fit to experimental data of polyurethane compared with traditional viscoelastic models.The fitting results indicate that fractional calculus Poynting-Thomson model has an obvious improvement in describing stress relaxation and creep response,while it is similar to traditional viscoelastic model in describing simple stretch response.Fractional calculus Zener model is used to characterize free recovery behavior of SMP with different memory factor,heating rate and temperature.Overall,fractional calculus model with fewer parameters can represent the viscoelastic response of SMP more accurately.Then the shape memory process of SMP is simulated by utilizing FEM based on software ABAQUS and the thermomechanical relations between stress,strain and temperature are studied in detail.The appearance of the phenomena that stress cure begins to decline and recover later is analyzed.Finally,the effect of temperature,thermal expansion coefficient,cooling rate and heating rate on SMP shape memory are studied.It is shown that modulus of elasticity of SMP degrades when rising temperatures;stress increment in the stress-freezing process also enlarges when enhancing thermal expansion coefficient and cooling rate;heating rate is correlated positively with shape/stress recovery temperature of SMP.