Abstract: In order to reveal the viscoelastic mechanism and conduct simulation of SM (shape memory) effect, the stress and strain evolutions and fixity ratio equation were derived from the generalized Maxwell model with time temperature superposition principle. Fixity ratio equation shows that the shape fixity ratio can be lifted by raising the ratio of holding time over tension time. The evolution equations reveal the viscous-elastic nature of the SM effect. The shift function is decreased because of the dropping of temperature, which will reduce the actual time and result in delaying of shape recovery. When the temperature raise up, the reducing effect is weakened, the shape recovery will occur. Simulation methods are established based on the viscoelastic model in Abaqus and user subroutine of Arrhenius equation and WLF equation. The material parameters of epoxy shape memory polymer are obtained by tension-relaxation tests. Then the test and simulation of SM process were conducted. Results indicate that the simulation methods are accurate enough, and Arrhenius equation results in more accurate simulations than WLF equation for epoxy SMP used in the tests.

Key words: shape memory polymer, generalized Maxwell model, stress and strain evolutions, time temperature superposition principle