Thermally actuated shape-memory polymers: Experiments, theory, and numerical simulations

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 10 −3 s −1 and 10 −1 s −1 , and at temperatures ranging from room temperature to approximately 30 C 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 numericallypredicted 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.

Experimental characterization and thermoviscoelastic modeling of strain and stress recoveries of an amorphous polymer network

“…Despite that fact, the number of papers dedicated to modeling shape memory polymers remains limited. We may divide the existing models into two categories: the models based on a bi-phasic representation of the material grounded on the rubbery/glassy state transition, first proposed by Liu et al (2006) and adopted by Chen and Lagoudas (2008), Qi et al (2008), Volk et al (2010), Gilormini and Diani (2012), and the thermoviscoelastic approach early introduced by Tobushi et al (1997) and improved by Diani et al (2006), Nguyen et al (2008), Castro et al (2010), Srivastava et al (2010), Diani et al (2012) and Yu et al (2012).…”

Some New Concepts of Shape Memory Effect of Polymers

“…A review of the literature gives a great deal of valuable information [12][13][14][15][16][17][18][19][20] about the SMPs; however the answers to a number of serious and foremost questions are still shrouded in mystery. For example, some macroscopic phenomena still lack a detailed understanding on the microscopic level.…”

On modeling shape memory polymers as thermoelastic two-phase composite materials

“…In the first type, Tobushi et al [4] developed a four-element variation of a viscoelastic rheological model, the numerical integration of which was detailed by Bhattacharyya and Tobushi [5], and that was extended to nonlinear effects by Tobushi et al [6], whereas Lin and Chen [7] could reproduce experimental results qualitatively with a mere 3-element standard linear solid by relating the dash-pot viscosity to temperature. A less macroscopic approach, using two coexisting substructures in the material, with different mechanical behaviors, was proposed by Kafka [8], while Qi et al [9], Nguyen et al [10], Srivastava et al [11] developed other models by taking advantage of the large amount of knowledge that is available on polymer physics. All these models, as well as those considered below, apply to amorphous shape memory polymers and do not account for the specific effects of crystallization that Barot and Rao [12] and Barot et al [13] included.…”