Thermo-mechanical modeling of semi-crystalline thermoplastic shape memory polymer under large strain

In this work, a constitutive mechanical model is proposed to describe the thermo-mechanical cycle of a semi-crystalline shape memory polyurethane which is able to recover its initial shape after applying more than 100% strain during a shape memory cycle. To explore this performance, experimental tests were conducted to determine the cyclic thermo-mechanical behavior of a polymer submitted to five shape memory cycles. Indeed, uniaxial tensile tests at small strain rates were performed at 60 degrees C in order to analyze its hyper-elastic response. At the end of the previous tensile loading, relaxation tests were carried out to determine the viscoelastic behavior during the shape memory cycle. The shape memory effect was investigated by means of free and constrained recovery experiments. These experimental results are used to identify the parameters of the constitutive model by means of curve-fitting algorithm employing leastsquares optimization approach. The proposed model is then implemented in the finite element software Comsol Multiphysics (c) and predicts quite well an in-plane strained cylindrical ring.