The presentation addresses the development of a constitutive model for crystallizable shape memory polymers (CSMP), which are are novel materials that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The crystalline phase is responsible for fixing the temporary shape, while the melting of crystals is responsible for returning to the original shape, i.e., shape recovery.
A set of constitutive equations has been developed to model the thermo-mechanical behavior of crystallizable shape memory polymers using elements of thermodynamics, continuum mechanics, and polymer science. Models are developed for the original amorphous phase, the temporary semi-crystalline phase, and the transition between these phases. Modeling of the crystallization process is done using a framework developed recently for studying crystallization in polymers based on the theory of multiple natural configurations. Using the same framework, the melting of the crystalline phase to capture the return of the polymer to its original shape is also modeled.
Predictions of the model are verified against experimental data available in literature and the agreement between theory and experiments is good. The model is able to accurately capture the drop in stress observed on cooling and the return to the original shape on heating. To solve complex boundary value problems in realistic geometries, a user material subroutine (UMAT) for this model has been developed for use in conjunction with the commercial finite element software ABAQUS. Practical use of the developed module is demonstrated for a fairly complex problem.