Failure of shape-memory polymers: Experimentation and modeling

Driven by practical applications, studies on the thermo-mechanics of shape-memory polymers (SMPs) grew in quantity and quality. Most of these studies are focused on experiments and modeling of the SMP deformation including phase transition. Various theories with essentially different approaches are available and compete. The present work deals with the less explored issue related to the SMP failure. Results of conducted experimental studies of the onset of damage are reported for a polymer whose shape-memory behavior is based on a glass transition temperature. These results are obtained under uniaxial tension as well as via bulge – membrane inflation – tests under varying temperatures. The combination of these tests provides a better understanding of SMP behavior, compared to the popular, and easier to perform, purely uniaxial tension tests which might give an inaccurate view of material response. Experimental results are further used for calibrating hyperelastic models of glassy and rubbery phases of the SMP material. Two novel features of the theory include a simple switch between descriptions of glassy and rubbery phases and enforcement of energy limiters in the constitutive equations to account for material failure. A general theoretical setting is also provided for modeling cracks, yet they are not simulated in the present work.