Investigation of deformation and shape memory characteristics of thermoplastic polymers

Yiğitbaşı, Cihan
Algorithmic implementation of constitutive models for shape memory polymers into commercial software packages through user material interfaces is the subject of this thesis. The effect of temperature change on the behaviors of these materials has been examined. The formulation of the generated material model has been constructed in the logarithmic strain space. Material model structure consists of three main steps. (i) In the geometric pre-processing step, using current and plastic metric, total and plastic logarithmic strain measures were defined, respectively. (ii) In the material model step, constitutive equations for (an)isotropic elasto viscoplasticity in the logarithmic strain space were identified in a structure analogous to geometrically linear theory. (iii) In geometric post-processor step, the objects obtained in logarithmic strain space were mapped back to their nominal, Eulerian or Lagrangian counterparts. After these three main stages, the 8-chain model with the double kink theory was used to define the flow rule for plastic strain in logarithmic strain space. All the material information that was theoretically defined was written as a FORTRAN code. A new term has been added to the tangent moduli calculations in order to run this code in ABAQUS. The obtained material model was verified by comparing with the test data in the literature. Finally, the shape memory effect of thermoplastic materials on a tube geometry is investigated in ABAQUS. The results suggest significant shape memory effect for plexiglass.