Finite strain viscoelastic model of shape memory polymer in Prony series form

To investigate the finite strain mechanical behavior of SMPs (shape memory polymers), a finite strain viscoelastic model was derived from the classical viscoelastic model in which the elastic and viscous mechanical response were formulated with Neo-Hookean hyperelastic model and Prony series respectively, and parameters fitting equations were derived in particular tensile case. Tension-relaxation tests of ESMP (epoxy shape memory polymer) were carried out to validate the proposed constitutive model, and the constitutive parameters were identified through nonlinear fitting using the derived parameters fitting equations. The experimental research on viscoelastic properties of ESMP at various temperatures was also conducted; the initial instantaneous modulus and the ratio of viscous modulus to the initial instantaneous modulus decrease when the temperature rises, but the elastic part modulus remains unchangeable. The numerical simulation method was developed by the proposed constitutive model and ABAQUS software, which could be used to solve three-dimensional problem of SMPs' structures. The tension-relaxation simulation tests were carried out, and comparisons between numerical simulations and experimental results demonstrates that the proposed constitutive model is reasonable in the finite strain analysis of SMPs structural problem. Meanwhile, the proposed method could be used in other kinds of isotropic viscoelastic polymers.