Three dimensional constitutive equation for shape memory polymers and its applications

Abstract

This thesis proposes new three-dimensional constitutive equation for shape memory polymer(SMP) and its possibilities for various applicatins. Differently from existing models, the new model is three dimensionally described, applicable to the problems with three dimensional geometry, able to deal with large deformation, usable for the composites which are combination of SMP and other materials and adoptable for the multiphysics situations.

The proposed model considers SMP as a parallel connection of rubbery and glassy phase and assumes non-mechanical strain exists in glassy phase to realize shape memory effect. These features are an idea obtained from the molecular structures of SMP and their behavior. The non-mechanical strain as a key element are calculated from principal stretches and principal directions of total deformation.

To validate the model, or to compare it to experiments, this thesis proposes the method of getting material parameters experimentally which are needed to the constitutive equation. And it also presents the comparisons experimental and three dimensional modeling results, which includes punching test as a multiaxial problem.

This thesis applies the new model to shell structure which exists in three-dimensional space. Because existing shell structural theories are applicable to only linear elasticity or pure inelasticity and not applicable to complex SMP constitutive equation, this thesis describes SMP constitutive equation for shell structure by using the method of midplane, the typical method for shell element. Then, the comparisons of the shell and experimental or three dimensional results are presented for the validation.

Theoretical studies on magneto-responsive SMP composites are dealt in this thesis because very few researches about this topic exist. A representative volume element (RVE) is set. SMP as a matrix and iron partices as reinforcements are input in this geometry. Then, mechanical behavior of this composites are investigated under various magnetic fields. These progresses will helpful to the prediction of the relation between the magneto-responsive SMP composites and magnetic field because experimental with real magnetic field is very difficult.

And the proposed model are tried to be applied to various physical situations to see the practicality and potential of the model.