ABSTRACT: With the aim of developing a thermo-mechanically-coupled large deformation constitutive theory and a numerical-simulation capability for modeling the response of thermally-actuated shape-memory polymers, we have (i) conducted large strain compression experiments on a representative shape-memory polymer to strains of approximately unity at strain rates of 0.001 /sec and 0.1 /sec, and at temperatures ranging from room temperature to approximately 30C above the glass transition temperature of the polymer; (ii) formulated a thermo-mechanically-coupled large deformation constitutive theory; (iii) calibrated the material parameters appearing in the theory using the stress-strain data from the compression experiments; (iv) numerically implemented the theory by writing a user-material subroutine for a widely-used finite element program; and (v) conducted representative experiments to validate the predictive capability of our theory and its numerical implementation in complex three-dimensional geometries. By comparing the numerically predicted response in these validation simulations against measurements from corresponding experiments, we show that our theory is capable of reasonably accurately reproducing the experimental results. As a demonstration of the robustness of the three-dimensional numerical capability, we also show results from a simulation of the shape-recovery response of a stent made from the polymer when it is inserted in an artery modeled as a compliant elastomeric tube.

News:

Understanding shape-shifting polymers

Details:

1. 1)Vikas Srivastava, Shawn A. Chester, and Lallit Anand, 2010. Thermally-actuated shape-memory polymers: experiments, theory, and numerical simulations. Journal of the Mechanics and Physics of Solids, 58 1100-1124.
   

Force Recovery

In this example we consider the force recovery of a specimen of shape-memory polymer.  In this case the specimen is deformed while above Tg, then cooled to below Tg and the grips fixed such that the displacement is fixed.  Then when heated back again to above Tg, the force is monitored.

Shape Recovery

In this example we consider the shape recovery of a shape-memory polymer.

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Vascular Stent

In this example we consider applying the constitutive theory to the application of a vascular stent.  In the simulation, the stent is compressed while above Tg, then cooled below Tg such that remains smaller that the artery, after placement in the artery, the stent is heated again and it pushes against the artery wall.  (Keep in mind that this a purely numerical exercise; no actual stent for humans is expected to be heated to 65C.)

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